WAVE EXPOSURE STUDIES
ON ROCKY SHORES IN SHETLAND
A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the Faculty of Science in the
University of London and for the Diploma of Imperial College.
by
ROBIN A.D. WRIGHT B.Sc.
\
University of London Imperial College of Science and Technology, Department of Botany and Plant Technology Field Station, Silwood Park, Ascot Berkshire. January 1981 Extracts from Oliver Goldsmith (1859):
Exposure. "Where the sea meets no obstacles, it spreads its waters with a gentle intumescence, till all its power is destroyed, by wanting depth to aid the motion* But when its progress is checked in the midst, by the prominence of rocks, or the abrupt elevation of the land, it dashes with all the force of its depth against the obstacle, and forms, by its repeated violence, that abruptness of the shore which confines its impetuousity."
Shelter M1he deafening noise of the deep sea, is here converted into gentle murmers; instead of the waters dashing against the surface of the rock, It advances and recedes, still going forward, but with just force enough to push its weeds and shells, by insensible approaches, to the shore,"
Northmavine, Shetland Hillswickness, Shetland
Frontispiece (iii)
ABSTRACT
The relevence of wave exposure studies to rocky shore monitoring is discussed, and an exposure scale developed for a biological monitoring programme in Norway is described. The same biological exposure scale is applied to the Shetland Islands and reformed to make one that is more appropriate to the new geographical area. An investigation is carried out into various aspects of the technique whereby shoreline sites are assigned to grades on the scale. The reliability of the exposure scale is tested, both spatially in relation to the effect of other environmental variables besides wave action, and temporally over different seasons and from year to year.
The physical basis of the exposure scale is examined through the measurement of wave impact pressures at a number of sites. The development and testing of an electronic wave pressure measuring system is described.
It consists of pressure sensors in the intertidal zone connected to an amplifier and chart recorder system upshore. The recorded wave pressures are discussed. A method for reducing the data into various statistics is outlined, and the significant wave pressures between sites are compared. An attempt is made to extrapolate the wave pressure records over a longer time scale, by considering long term records of wind speed and wave height.
The biological exposure scale is believed to be an approximately inverse expression of wave action, and this conclusion is supported by changes in various characteristics of certain species over the exposure range. A hypothesis is developed as to the way in which wave action influences rocky shore ecology. CONTENTS PAGE
FRONTISPIECE ii
ABSTRACT lii.
PART I INTRODUCTION 1
The Relevance of Wave Exposure Studies to Biological
Monitoring 1
The Shetland Islands 3
Early Attempts at Estimating Wave Exposure 7
PART II THE SHETLAND EXPOSURE SCALE 17
CHAPTER 1. The Shetland Exposure Scale - Introduction 17
CHAPTER 2. The Preparation of the Exposure Scale 18
2.1 Raw Data Collection 18
2.2 Application of the Norwegian Scale 27
2.3 Formation of the Shetland Scale 34
2.4 The Exposure Scale in Practice 47
CHAPTER 3. A Critical Assessment of the Exposure Grading Technique- 5 3
3.1 Data Collection - Abundance Measurement 53
3.2 Data Collection - Selection of Different Vertical
Intervals 60
3.3 Preparation of Exposure Scale - Cycling of Computer
Smoothing Process 63
3.4 Operation of Exposure Scale - Effect of Using a
Different Species Selection 67
3.5 Summary 72
CHAPTER 4. The Effect of Environmental Variables other than
Wave Action on Exposure Grade 73
4.1 The Environmental Variables 73
4.2 The Environmental Variables Related to Exposure Grade- 82
4.3 The Relative Importance of the Environmental Variables- 96 (v)
TAGE
4.4 The Effect of Secondary Physical Factors on
Exposure Grade 103
4.5 The Abundance of Fuous vestculosus Related
to the Particularity of the Substrate 115
CHAPTER 5. The Effect of Time on Exposure Grade 120
5.1 The Seasonal Study at Mavis Grind 121
5.2 Annual Variation in Exposure Grade 143
CHAPTER 6. The Shetland Exposure Scale - Summary 147
PART III MEASUREMENT OF WAVE ACTION ' 150
CHAPTER 7. Measurement of Wave Action - Introduction 150
CHAPTER 8. Wave Pressure Measuring Equipment 155
8.1 Selection Criteria 155
8.2 The Equipment Described 156
8.3 Initial Field Trials 164
CHAPTER 9. Data Collection at Mavis Grind, Shetland 170
9.1 Calibration of the Wave Pressure Measuring
Equipment. 170
9.2 Recording at MG6 - MG9 172
9.3 Recording at MG2A - MG3A 184
CHAPTER 10. The Wave Pressure Records Described 189
10.1 The Magnitude of Wave Pressures Recorded 189
10.2 Variation in Wave Pressure at One Site 196
10.3 Shock Pressures 207
10.4 Instrument Testing 209
CHAPTER 11. Processing the Wave Pressure Records 216
11.1 Digitising and Data Reduction 216
11.2 Wave Pressure Related to Wind Speed and Wave Height- 231
11.3 A Comparison of Wave Pressures Between Sites 240 vi)
PAGE
11.4 Extrapolation of the Wave Pressure Records 249
CHAPTER 12. Measurement of Wave Action - Discussion and
Conclusions 271
PART IV SPECIES CHARACTERISTICS IN RELATION TO WAVE ACTION 275
CHAPTER 13. Morphology 275
13.1 Introduction 275
13.2 ]\lucella lapiHus 278
13.3 Lcminaria d-igi-tata 281
13.4 Fuous ves-Cculosus 286
CHAPTER 14. Height of Zones 291
295 PART V SUMMARY
The Usefulness of the Biological Exposure Scale 295
The Exposure Scale Related to Wave Action 297
ACKNOWLEDGEMENTS 302 REFERENCES 304
APPENDICES 315
MICROFICHE See Back Cover Cvii)
FIGURES PAGE
2.1.1 The Cross-staff 20
2.1.2 Example of Site Location Sheet 22
2.1.3 Example of Biological Recording Sheet 23
2.1.4 Location of Sites in Shetland 24
2.2.1 The Distribution of "free-living" Fucoids in Relation to
Salinity 33
2.3.1 Reciprocal Averaging - Species Coordinates 35
2.3.2 Reciprocal Averaging - Site Coordinates 35
2.3.3 Modified Maximum Fetch vs. Axis 1 of Reciprocal Averaging 38
2.3.4 Axis 1 of Reciprocal Averaging vs. Norwegian Exposure Grade 39
2.3.5 Diagram of Exposure Scale Programs 43
2.3.6 Abundance Curves of Fuous Vesioulosus and Ascophyllum nodosum— ^4
2.3.7 Abundance Curves of A'laP'ia esculenta and Mytilus ^dulis 45
2.4.1 Location of Sites and Exposure Grades around Mavis Grind 49
2.4.2 Location of Sites and Exposure Grades at Whale Firth, Yell
and Gletness 51
3.2.1 Kite Diagrams for Selected Species at MG9 Assessed at
Different Vertical Intervals 62
3.3.1' Effect of Cycling Computer Smoothing Process on Abundance
Curves of Selected Species 65
3.4.1 Coefficient of Similarity vs. Exposure Grade for 0P55
using May 78 Data 71
4.1.1 Roughness Ratio Frequency Histogram - 80
4.1.2 Example of a Physical Data Sheet 81
4.2.1 Depth Offshore Variables vs. Exposure Grade 84
4.2.2 Angle of Sea Horizon and 90° Fetch vs. Exposure Grade 85
4.2.3 Maximum Fetch and Modified Maximum Fetch (Logarithms) vs.
Exposure Grade 88 Cviii)
PAGE
A.2.A Modified Fetch 5 arid Modified Fetch 6 vs. Exposure Grade 89
A.2.5 Angle of Transect in Relation to Max Fetch and Aspect vs.
Exposure Grade 91
A.2.6 Texture and Degree of Fissuring vs. Exposure Grade 92
A.2.7 Angle of Slope and Roughness Ratio vs. Exposure Grade —- 93
A.2.8 Percentage of Stones on Transect and Salinity vs. Exposure
Grade 9A
A.2.9 Correlation Coefficients between Environmental Variables
and Exposure Grade 95
A.3.1 Distribution of the Environmental Variables on the First
Eigen Vector of the Principle Components Analysis 98
A.3.2 Vector 1 vs. Vector 2 for Sites in Principle Components Analysis- 99
A.3.3 Plots of Reciprocal Averaging Ordinations 101
A.A.I Observed vs. Expected Exposure Grade 105
A.A.2 Observed - Expected Exposure Grade vs. Angle of Transect in
Relation to Max Fetch and Aspect 107
A.A.3 Observed - Expected Exposure Grade vs. Angle of Slope and
Roughness Ratio 108
A.A.A Observed - Expected Exposure Grade vs. Texture and Degree
of Fissuring 109
A.A.5 Observed - Expected Exposure Grade vs. Percentage of Stones
and Silt on Transect ' HO
A.A.6 Observed - Expected Exposure Grade vs. No. Stones Top and
Middle of Transect HI
A.A.7 Observed - Expected Exposure Grade vs. No. Stones on Bottom
of Transect and Salinity 112
A.5.1 Maximum Abundance Score for Fuous vesiculosus vs. Percentage
of Stones on the Transect 118
5.5.1 Location of Proposed Transect Sites and Water Sample Sites
at Mavis Grind (ix)
TAGE
5.1.2 Nitrogen and B.O.D. Concentrations around Mavis Grind-Feb 78 126
5.1.3 Change in Exposure Grade with Time for Mavis Grind (MG) Sites— 129
5.1.4 Wind. Speeds and Maximum Temperatures at Lerwick in 1978 134
5.1.5 Monthly Mean Temperatures and Wind Speeds for Lerwick 1978
- 1980 138
5.1.6 Coefficient of Similarity vs. Exposure Grade for MG2 using
Data Collected in 1978 140
5.1.7 Changes in Species Maximum Abundances at MG2 1978 - 1980 141
8.2.1 The Soil Pressure Cell 159
8.2.2 Flow Diagram of Wave Pressure Measuring Equipment 163
8.3.1 Details of a Climbing Bolt 166
8.3.2 Location of Testing Sites at Dale Fort, Dyfed 167
9.0.1 Location of Wave Pressure Recording Sites and Equipment at
Mavis Grind 171
9.2.1 Details of Hut 173
9.2.2 Location of Wave Pressure Measuring Equipment at MG6-9 176
9.2.3 The Wave Staff 179
9.3.1 Location of Wave Pressure Measuring Equipment at MG2A and
MG3A 186
10.1.1 Trace of Section of Trace 18 190
10.1.2 Trace of Section of Trace 78 192
10.1.3 Trace of Section of Trace 67 - MG3A 194
10.2.1 Details of Rawbolt and Cable Clip 198
10.2.2 Positions of Transducers and Cable Clips on MG9 199
10.2.3 Typical Wave Forms from Four Transducers Mounted on MG9 -
Trace 78 201
10.2.4 Location of 0P70 and Positions of Transducers and Cable Clips— 203
10.2.5 Typical Wave Forms from Three Transducers Mounted on 0P70 -
Trace 91 206 10.4.1 Transducer Testing Rig
10.4.2 Sketch of Long Section of Wind Tunnel
10.4.3 Wind Speed Recorded by Cup Anemometer vs. "Real" Wind Speed
Measured by Betz Guage
11.1.1 A Section of Digitised Trace from MG6 - Trace 31
11.1.2 Section of Digitised Trace from MG7 - Trace 31
11.1.3 Section of Digitised Trace from MG8 - Trace 31
11.1.4 Section of Digitized Trace from MG9 - Trace 31
11.1.5 Section of Digitized Trace from MG2A - Trac6 57
11.1.6 Section of Digitised Trace from MG3A - Trace 67
11.2.1 Wind Speed and. Wave Height vs. Wave Pressure for MG2A
11.2.2 Wind Speed and Wave Height vs. Wave Pressure for MG3A
11.2.3 Wind Speed and Wave Height vs. Wave Pressure for MG6
11.2.4 Wind Speed and Wave Height vs. Wave Pressure for MG7
11.2.5 Wind Speed and Wave Height vs. Wave Pressure for MG8
11.2.6 Wind Speed and Wave Height vs. Wave Pressure for MG9
11.3.1 Significant Wave Pressure vs. Exposure Grade
11.3.2 Mean Significant Wave Pressure vs. Exposure Grade
11.3.3 Mean Wave Forms for MG6 - MG9 - Trace 31
11.3.4 Mean Wave Forms for MG2A and MG3A - Traces 57 and 67
11.3.5 Mean Wave Forms for Four Transducers on MG9 - Trace 78
11.3.6 Mean Wave Forms for Three Transducers on 0P70 - Trace 91
11.4.1 Significant Wave Pressure vs. Mavis Grind Wind Speed - MG2A
11.4.2 Mavis Grind Wind Speed at MG2A vs. Lerwick Wind Speed
11.4.3 Significant Wave Pressure vs. Lerwick Wind Speed - MG2A
11.4.4 Percentage Exceedence Curve of Wind Speed Effective for
Producing Waves at MG2A (Lerwick Data)
11.4.5 Significant Wave Pressure MG8 vs. MG8 Wave Height
11.4.6 MG8 Wave Height vs. Yell Wave Height
11.4.7 Significant Wave Pressure MG8 vs. Yell Wave Height (xi)
PAGE
11.A.8 MG8 Wave Height vs. Foula (Fitzroy) Wave Height 265
11.4.9 Significant Wave Pressure MG8 vs. Foula (Fitzroy) Wave
Height 266
11.4.10 Time Series of Wave Heights 268
11.4.11 Percentage Exceedence Curve of Wave Height for Fitzroy
(Foula) Dec 1973 - Nov 1978 270
13.2.1 Variation in the Shape of Pembrokeshire (Dyfed) Populations
of NuceZZa Zap-iZZus with exposure. Drawn after Crothers (1973)- 279
13.2.2 Variation in the Shape of Shetland Populations of NuceZZa
ZapiZZus Drawn after Crothers (1979) 279
13.3.1 Variation in Morphology of Laminar-ia di-g-itata with Exposure
to Wave Action 282
13.3.2 Histograms of Lamina Base Angles 283
13.3.3 Mean Lamina Base Angle vs. Exposure Grade —— 285
13.4.1 No. Vesicles vs. Fresh Weight of Fuous vesicuZosus in
Relation to Exposure Grade 290
14.0.1 Black Lichen Height vs. Exposure Grade 293 (xii)
TABLES PAGE
2.1.1 Site Locations and Exposure Grades 25
2.3.1. Simplified Version of Shetland Exposure Scale 46
3.1.1 CSU and OPRU Abundance Estimates for MG6 - MG9 56
3.1.2 Exposure Grades from OPRU and "CSU" Methods 58
3.2.1 Selection of Different Vertical Interval in Relation to
Exposure of Shore 60
3.4.1 Species Selection for Exposure Grade Production 68
4.3.1 Multiple Regressions between Exposure Factors and Exposure
Grade 102
4.4.1 Observed - Expected Exposure Grade (Y) vs. Secondary Physical
Factor (X) Regressions, with Limits on the Latter Variables 114
4.5.1 Abundance of Fuous vesiculosus and Particularity Data 116
4.5.2 Correlation Coefficients between F. vest-culosus and
Particularity Factors 117
5.1.1 Water Quality Around Mavis Grind 124
5.1.2 Exposure Grades in Different Seasons at Mavis Grind 127
5.1.3 Correlations between Changes in Species Maximum Abundance
and Exposure Grade 130
5.2.1 Annual Exposure Grades from Selected OPRU Sites 144
8.1.1 Maximum Wave Pressures Previously Recorded 155
9.2.1 Summary of Major Events at MG6 - MG9 in May/June 1979 181
9.2.2 Change in Transducer Calibrations after Repair 182
11.1.1 Print from Magnetic Tape Storage of Section of Trace 31 219
11.1.2 Print' from Permanent File RIPPLE 228
•11.2.1 Wind Speeds and Wave Heights at Mavis Grind. Print from
Permanent File WIND 232
11.3.1 Maximum and Mean Significant Wave Pressures 242
11.4.1 Wave Pressure and Wind Speed at MG2A with Wind Speed at Lerwick- 257 11.4.2 Annual Hourly % Wind Speeds Lerwick 1957 - 1978
11.4.3 Significant Wave Pressures at MG8 and Simultaneous Wave
Heights
13.3.1 Exposure Grades and Mean Laminaria d-igitata Lamina Base
Angles for Selected Sites
13.4.1 Fresh Weight and No. Vesicles on Fucus Vesiculosus Plants
from' Selected Locations
14.0.1 Exposure Grades and Black Lichen Heights ("xiv)
PLATES PAGE
8. 2. 1 Complete Pressure Cell —— 157
8. 2. 2 Damaged Pressure Cell with no Silicon Rubber 157
8. 2. 3 Damaged Pressure Cell. View Under Force Collecting Plate 157
8. 2. 4 , Close-up of Semiconductor Header 157
8. 2. 5 Recording Instruments in Hut 161
8. 3. 1 Wave Trace from Dale Fort Pier - 5 mm/s 169
8. 3. 2, Wave Trace from Dale Fort Pier - 25 mm/s 169
8. 3. 3 Wave Trace from Dale Point - 5 mm/s 169
9. 2. 1 Equipment Installed at MG6 - MG9. Minn in Background 177
9. 2. 2 Transducer and Hosepipe Containing Cable on MG8 177
10. 1. 1 Section of Trace 31 192
10. 1. 2 Section of Trace 57 - MG2A 194
10. 2. 1 A Section of Trace 82 - 0P70 204
10. 3.. 1 Shock Pressures from Trace 82 - 0P70 208 PART I
INTRODUCTION 1
The Relevance of Wave Exposure Studies to Biological Monitoring
In the construction and operation of a new oil terminal or refinery,
it is desirable to be able to monitor any changes in the environment that may be attributed to.the installation during its subsequent operation.
In coastal situations, this usually involves measuring or estimating
the abundance of selected species at a number of fixed sites in the rocky shore littoral region, and assessing the importance of changes that seem to have occurred over the monitoring period. It is obviously an advantage to have started monitoring several years before the con-
struction phase so as to have plenty of baseline data, but as Baker (1976a) points out, this is often lacking. Many monitoring programmes have two or three years baseline data, but conclusions from such short periods should be viewed with caution. Although short baseline studies of two or
three years duration provide a useful framework for subsequent monitoring,
they cannot be used to describe adequately the "natural" situation where population densities are rarely stable from year to year. Indeed,
longer term studies show that natural populations situated far from industrial installations are in a constant state of flux due to a complex of physical and biological factors (Lewis, 1964; Jones et al., 1980).
Natural fluctuations in population density after commissioning may make
trends due to chronic pollution difficult to detect, and according
to Lewis (1976), this may limit the value of long term abundance measurements if their aim is to detect subtle changes in water quality.
Because of this problem, an important additional aid in assessing
the importance of change at any one site is the use of reference or control
sites located outside the influence of the installation. In order to be able to compare these sites with ones closer to the installation,
it is important to understand the main environmental factors at work on
the shores (Dalby, Cowell and Syratt, 1978). This allows sites that • 2 would be similar under natural conditions to be selected and compared, and may help to explain differences between them. The research project described in this thesis arose from a need to have a better understanding of a very important environmental factor influencing the ecology of rocky shorelines - the amount of wave action.
In 1972, ecologists from British Petroleum began a series of rocky shore surveys around a proposed new refinery at Mongstad, Fensfjord in
Western Norway. It was soon apparent that the main environmental variable influencing the ecology of the shores in the area was indeed exposure to wave action (Syratt and Cowell, 1975).
In order to be able to classify selected shoreline sites in terms of exposure, a biological exposure scale (Ballantine, 1961) was applied to the data. With this technique, the environmental continuum from exposure to shelter is divided into a number of grades in each of which a typical biological community is recognised. Baseline data from Mongstad were collected for three years prior to commissioning in 1975, and subsequent monitoring has continued on an annual basis (described in
Monk, Cowell and Syratt, 1978; Syratt, Monk and Wright, 1980). Over the first part of this period, the exposure scale was refined and eventually published (Dalby, Cowell, Syratt and Crothers, 1978). In its refined form, sites could be attributed more precisely to a grade of exposure in which the expected biological community had been carefully described.
It was soon realised that an understanding of the wave exposure gradient would be an invaluable aid to rocky shore monitoring at sites other than Mongstad. It was decided to look into the capabilities of the biological exposure scale and attempt to describe it more accurately in terms of physical measurements of wave action.
BP's Environmental Control Centre has generously supported this project at Imperial College, London. Jc In subsequent text references (apart from quotations from other sources) the word "exposure" used unqualified means "exposure to wave action". The Shetland Islands
The Shetland Islands were chosen as the location for the field- work for the present study. Situated on approximately the same latitude as Bergen in Norway, the Shetlands (60°N, 1°W) are an isolated group of islands where traditional occupations include fishing, crofting and knitting. This rural economy was drastically altered in the 1970*s when oil was discovered to the east of Shetland. Service and supply bases were established, and in 1975, the construction of an £800m. oil terminal was started on Calback Ness, Sullom Voe, to handle oil from the Ninian and Brent fields (Marshall, 1978). Through the Sullom
Voe Association (SVA), BP were nominated as the managers for the con- struction of the terminal. The Shetland Oil Terminal Environmental
Advisory Group (SOTEAG), which advises the SVA on environmental matters, is responsible for coordinating various environmental monitoring pro- grammes mainly in the neighbourhood of Sullom Voe. The support that could be given by the various organisations working for SOTEAG was undoubtedly one of the reasons for selecting Shetland as the location for this research project. In addition, it was considered interesting to attempt to apply principles developed in Western Norway to a similar environment in a different geographical area.
The coast of Shetland is ideal for wave exposure studies. For 2 a land area of approximately 1440 km , its coastline length of about
1450 km. means that it is extremely involuted. The indentations in the coastline are in the form of long narrow bays (voes) that provide a sheltered low-lying "inner coast" distinctly different in character from the exposed cliffs which form the "outer coast" (Flinn, 1974).
The penetrating nature of these voes means that although the maximum dimensions of the largest island of Shetland (Mainland) are approximately
100 km. (N-S) by 40 km. (W-E) , no point is further than about 5km. from the sea. A wide range of shoreline environments from exposed to sheltered may be found over a short distance.
The tidal range of the waters around Shetland is small, being only 0.70 m. at neap tides and 1.70 m. at spring tides (Admiralty
Hydrographic Department, 1980). There is a tidal lag of approximately two hours from the west to the east side of the islands, and there are strong tidal currents at a number of locations. On the outer coast, there are few sandy beaches, most of the shorelines having a solid bedrock substrate with little loose material. The angle of these shores is generally fairly steep, typically in the region of
20° to 30°. On the inner coast, the solid bedrock shores often give way to gently sloping shores with a more particulate substrate consisting of small angular boulders (typically 5-10 cm. for any dimension). For the purposes of this study, shoreline sites on solid bedrock substrates were chosen wherever possible.
The combination of a steep shore and a small tidal range means that generally the length of a transect from low water to the first flowering plants is rather small. In sheltered areas, the littoral zones may be compressed to form a transect of only 3 m., but a transect length for an area of moderate exposure is more like 10 TO. At very exposed sites where the spray from waves reaches considerably further, littoral zones may be uplifted and extended over a transect length of 40 or 50 m. The generally small shore transect length in Shetland is convenient for wave exposure studies. Biological data is relatively easy to collect because the zonation is compact on a typically regular steep surface. Waves appear to break evenly on this sort of surface, and there is unlikely to be much difference in wave exposure between the bottom and the top of the shore.
The range of exposure conditions to be found in Shetland may be 5
illustrated by reference to two contrasting areas. The Vadils (HU290 550)
is a complex area of little bays situated at the seaward end of a long narrow voe. Since the open sea is over 6 km. away, the casual observer
looking across The Vadils might easily mistake them for an area of
interlocking freshwater lakes lying in the bottom of a heather covered basin. However, a closer inspection of the shore would reveal the characteristic blanketing cover of Ascophyllum nodosum, indicating
that the water is indeed salty. The maximum fetch across The Vadils
in any direction is no more than about 0.5 km., and so even a strong wind only produces waves of a few centimetres in height which does no more than rustle the Ascophytlum. Most of the shoreline around The
Vadils is rather flat and composed of small stones and some silt. However, there are also one or two steep promontories formed of stable bedrock where the limited zonation provided by the small tidal range may be observed. At high tide, the seaweed zones are completely submerged, leaving only a narrow splash zone of lichens separating the sea from the flowering plants.
The Grind of the Navir (HU 213805), on Shetland's outer coast at Eshaness, is an unusual rock formation on a 30 m. high cliff. "Grind" is an old Norse word meaning gate, and the "gate" in this case is an opening flanked by two high towers of rock (see illustration on frontispiece). The steep descent to the shore is over lumpy bedrock which is covered in a mixture of black lichens and blue-green algae, which are very slippery when wet. Due to swell conditions, it is usually impossible to reach the other algal zones, and it is only on exceptionally calm days when these shores may be examined in detail. The constant wetting of the shore means that the algal zones are greatly uplifted and extended from the tidal area. The topshore is dominated by a slippery covering of species such as Porphyra umbilicalis. When the swell pulls back from the lower shore, bright pink patches of "lithothamnia" may be seen through the dense covering of mussels. Battered strands of
AZavia esouZenta complete the lower shore scene. On a rough day, it is impossible to approach this kind of coast. An enormous Atlantic
swell, rolling and crashing against the rock, will come rushing up
the shore and through the "gate" at the Grind of the Navir, some 25 m. above mean sea level. There is evidence to the power of this surge
in the form of a storm beach behind the "gate" consisting of large blocks of rock each weighing several tonnes. Russel and Macmillan
(1952) report a similar feature on Bound Skerry in the Shetlands, where they estimate that 9{ ton blocks of rock have been moved upshore
to a position 62 ft. above low water mark and 330 ft. from it. Ad- jacent to the Grind of the Navir is the Head of Stanshi where there is a low rock barrier over which the swell may occasionally push a
surge of water to come crashing down into a pool behind it. These
spectacular results are typical of exposed rocky shores in Shetland where the many offshore stacks and natural arches may provide similar conditions. 7
Early Attempts at Estimating Wave Exposure
"So awful is the spectacle of a storm at sea, that it is generally viewed through a medium which biases the judgement; and, lofty as waves really are, imagination makes them loftier still." (Goldsmith, 1859).
Estimates of the height of ocean waves made by casual observers are nearly always too great, and it seems that as the waves get larger, so the exaggeration becomes worse. In Goldsmith's time, there were no accurate methods for measuring wave height offshore, and perhaps the best estimates of the severity of storms were provided by lighthouse keepers who could indicate the height of the waves by reference to the lighthouse or a fixed point on the shoreline. Their stories make awesome reading; as reported by Johnson (1919) :
"At the Bell Rock lighthouse in the North Sea a groundswell, without the aid of wind, drove water to the summit of the tower 106 feet above high tide, and broke off a ladder at an elevation of 86 feet and at Unst, in the Shetland Islands, a door was broken open at a height of 195 feet above the sea".
The first serious attempts to measure the force of these enormous waves came from the lighthouse designer and engineer, Thomas Stevenson.
He was responsible for the construction of many lighthouses around the
British Isles, including the most northerly - Muckle Flugga, off the north coast of Unst, Shetland. With his experience of coastal structures, he was aware of the scale of the task he was embarking upon:
"Not withstanding the want of all direct measurements on this subject, and the somewhat unpromising nature of such an enquiry, I was nevertheless induced to attempt the construction of an instrument to affect the desired end; and after several fruitless designs had been put to the test, I at length succeeded in forming one whose indications I hope to be able to show are trustworthy." (Stevenson, 1849). 8
Stevenson called his chosen device a dynamometer. It consisted
of a structure similar to a railway buffer that was attached to a
shoreline or breakwater such that the impact pressure of the waves
could be measured. Initially, only maximum pressures over a given
duration could be recorded, but later instruments included a drum
actuated by clockwork such that the pressure of every wave could be
recorded (Hiroi, 1920).
In order, to obtain more precise measures of impact pressures
and wave forms, engineers interested in this subject moved to elec-
trical systems as soon as they became available. These will be des-
cribed in detail in Part III. Biologists interested in wave exposure
were not concerned with the individual wave. They wanted a quick method
of providing a value which would represent the exposure status of
any particular site, hopefully integrated over a long period of time.
This gave rise to many simplistic attempts to estimate wave exposure
from meteorological data or maps.
Moore (1935) recognised many important quantities that should be
known for the calculation of an "exposure factor" from meteorological
data. However, her "exposure factor" ignored most of these observations,
being simply "the number of days in a hundred days in which wind blows
into the aperture (which is the seawards aperture measured at a distance
of half a mile)." Moore's exposure scale thus ranged from 0 (shelter)
to 100 (exposed), but in practice only ranged from about 20 to 80,
with most shores grouped around a very small range in between these
extremes. The omissions from Moore's physical exposure scale are
obvious. No account has been taken of wind speed or fetch, nor indeed
of the influence of swell or coastal configuration on wave refraction.
Consequently the scale is virtually useless in a small scale study, as was demonstrated by Lysaght (1941) when he attempted to apply it to sites within Plymouth Sound. He found that for many of his sites, the seawards aperture measured at a distance of half a mile was 180°, but still within the Sound. A more appropriate aperture would have been that provided by the two headlands at the entrance to the Sound, some one and a half miles distant.
Southward (1953) tried to modify Moore's scale by adding a factor of wind speed. Southward was particularly interested in the height of the wash above predicted tidal levels in relation to wind speed.
At Port St. Mary in the Isle of Man, he noticed that all winds with a velocity of 10 knots or more produce a wash in excess of 1 foot above the theoretical tide level. Thus the modified exposure factor was based on the % frequency of winds in excess of 10 knots. He recognised that other data needed to be included as well as the "exposure factor" in order to give a relative exposure grading of a number of shores.
Therefore a comparison of his shores in any one locality was based more specifically on the relative wash heights. Southward and Orton
(1954) used Southward's exposure factor when they were investigating the effect of wave action on the ecology of Plymouth Breakwater.
Although Southward's assessment of exposure was an improvement on Moore's, it was clear that many variables were being omitted using these very indirect measures of wave action. Evans (1947) and Guiler
(1949) tried to correct this deficiency by including many more physical factors which may modify wave action. Evans (1947) considered the orientation of the rock and the proximity to sheltering masses with regard to the waves and direction of prevailing winds. He also con- sidered the angle of slope of the shore and the range of species in relation to tidal levels. This enabled him to produce a five point scale with which to rank shores in relation to wave exposure. This approach has to its advantage the fact that a large number of variables have been considered, but its disadvantage is that it is purely subjective and none of the variables have been measured. It is therefore not applicable to other areas, and cannot be used by other workers. Guiler
(1949) produced a semi-quantitative description of the wave exposure
of a shore by using a measured scale for each of the physical factors
that he though would influence wave action. The exposure of the shore was thus described in a form of code. For example; an open rocky coast on a volcanic island in mid-ocean in a gale force wind would be o84,a3, where o means oceanic location, 8 is the force of the wind given in
the Beaufort Scale, 4 is a fetch category, and a3 means an exposed
coast with fully exposed surfaces.
It is plainly obvious that any attempt to estimate the indirect
constituents of exposure cannot include all the factors involved.
Some general criticisms from Lewis (1964) emphasise this point. Local
topography will complicate physical estimates of exposure in that a flat shore and/or irregular coastline will allow gradual energy dis-
sipation up the shore which will have less exposure than predicted.
On the other hand, waves tend to be refracted parallel to the shore which may cause more exposure than expected. Heterogeneous conditions will change the exposure based on physical attributes both spatially
and temporally. In essence, the estimates of exposure based on the physical attributes of the shoreline, being based on correlations,
are designed to predict the effect of wave action and these physical predictions are unreliable since they cannot include all the variables
that influence wave action. Attempts to estimate exposure from the
effects of wave action may well be more fruitful. It is well documented
(Lewis, 1964), that the prime factor in determining the flora and fauna
on rocky shores is in fact wave exposure. If it is assumed that other
factors have a minimal effect, then the flora and fauna can be used 11
as an indicator of the amount of wave action. This is the basis of
the biological exposure scale.
The first biological exposure scale for rocky shores was described by Ballantine (1961). He recorded the abundance of certain indicator species on a number of shores in the Dale area of Pembrokeshire using abundance categories developed by Crisp and Southward (1958). The shoreline sites were separately ranked according to the abundance of each species in turn, the final order for the shores being an average of these individual rankings. Since it was clear that the final order made sense in terms of wave exposure, it was divided up into a number of groups or grades from each of which the mean abundance category for each species could be produced. This standard set of species abundances for each grade comprised the exposure scale with which any nev shoreline site could be compared. Ballantine divided his shores into eight grades of exposure ranging from Grade 1 (exposed) to Grade 9
(sheltered).
The idea of dividing a ranked order of shorelines into groups was adopted by the Institute of Terrestrial Ecology (1977) in a survey of rocky shores in Shetland. They used ordination analyses to rank the shorelines separately according to physical and biological data.
Both rankings appeared to list the shorelines in order of wave exposure, although the grades of each ranked scale did not appear to be inter- changeable. Although this work was not pursued, it demonstrated the assistance that numerical techniques could give to the ranking of
shores.
It was soon appreciated that the biological exposure scale pro- vided a quick and easy technique for comparing shoreline sites in terms of wave exposure. However, from the outset Ballantine was careful to 12
stress the limitations of the scale. The most obvious one is that it is
based on a circular argument - a shore is judged to be exposed because
it has a certain community pattern, but it has that community pattern
because it is exposed. This certainly does not invalidate the scale,
but without an independant variable it does mean that the physical
basis for the scale must be examined for each new study area. Pre-
viously, this has been done subjectively, whereas more confidence could
be placed in the scale if a more objective check on wave exposure was
devised. In practice, it has been found difficult to apply Ballantine1s
scale directly to a different geographical area - while functioning
satisfactorily in south-west England, it does not work in Spain or
Norway. The reason may be found in the varying ecological tolerances
of organisms in different climates which determine the organisms'
distribution. For example, climatic forces influence the relative
competitive ability of fucoids, limpets and barnacles making a community
on a northern exposed shore seem similar to that on an apparently
more sheltered southern shore (Ballantine, 1961). It is clear that
a new biological exposure scale would have to be formed for each new
area. Thus for example, would a Grade 1 shore in Norway be equivalent
in terms of wave exposure to a Grade 1 shore in Pembrokeshire? Again,
direct physical measurement would be required to check this. Further
criticism of the exposure scale concerns the arbitrary way in which
the scale is divided up into grades. While it is clear that the grades are in the correct order, with respect to wave exposure, (this can be confirmed by examining the progression from sheltered bay to exposed headland) , it is not certain that the grades are evenly spaced along the scale.
This is another problem that could perhaps be solved by direct measure- ment of wave action. Finally, Ballantine stressed that for proper use of the scale, only those shoreline sites where wave action is the dominant environmental variable should be selected. These sites should be of 13
constant slope, have an even surface, and should be uninfluenced by
factors such as a salinity reduction.
Bearing in mind these limitations, Dalby et al (1978) attempted
to apply the exposure scale concept to rocky shores in Western Norway.
Using Ballantine's scale as a guide, they dropped certain species
from the scale and included others depending on their relative importance
in Western Norway compared to Pembrokeshire. They also used a modified
abundance scale for certain organisms so as to increase the categories
of abundance from five to seven for better definition. Probably the
most significant advance was that the formation of the exposure scale
was put on a stricter numerical basis. This allowed intermediate
grades of exposure to be recognised when assigning a shore to a particular
exposure grade. The numerical techniques will be described fully in
Part II. It is clear that considerable advance has been made on the
original Ballantine method for assessing exposure.
Lewis (1964) is not so enthusiastic about the use of biological
exposure scales although he produced one himself! He recognises the
importance of other factors besides exposure in determining the biology
of the shore, and feels that a successful exposure scale should make allowances for the variables. Lewis states that his scale "relates primarily to uniform areas of bedrock at angles of about 20 - 50° in
full sunlight, but certain allowances for variation of slope and substrate are included." When examining his scale, this is not immediately apparent but it may prove to be the case in practice. Lewis's other main criticisms are that biological exposure scales do not allow for geographical differences and that the erratic spatial and seasonal distribution of some species may be confusing. His exposure scale is based on five communities of organism characterising* the five different grades of shore ranging from (1) which is very exposed to (5) which is very sheltered. Reference to the abundance of various organisms
is very subjective and in the main is limited to descriptive terms
such as "dominant," "abundant" and "present". The classification of
a shore by Lewis's method depends purely on a comparison of shore
descriptions.
The Lewis approach would appear to use the overall character of
the community as a guide to the exposure. Extremely exposed and ex-
tremely sheltered communities may be easy to distinguish, but the
intermediate ones may be more difficult. Lewis feels that it is
advisable to have a small number of subdividions on the exposure scale.
A larger number of categories may be possible in a local area such as
Pembrokeshire (c.f. Ballantine, 1961) because complicating differences
such as tides, geology etc., are kept to a minimum. In the more
widely applicable exposure scale suggested by Lewis, the smaller number
of categories must be distinct in that each must encompass all the
vagaries of the indicator species in that category. Each category must also allow for variations in the population caused by local factors
other than exposure. Finally the categories must permit sub-division,
where locally justified, into different geographical areas.
At this stage, it must be pointed out that in many of these
exposure scales there is a dilemma. In Lewis's biological exposure
scale, he strives for perfection in limiting the effect of variables other
than exposure. The only way he can do this is to reduce the number of
grades in the scale and make them more subjective, thus each grade on
the scale is broader and the sensitivity of the scale is lessened.
It is clear that a balance must be struck between perfection and
apparent sensitivity (objectivity). In a similar way, the perfect
physical exposure scale is one that objectively describes as many
of the physical attributes that influence wave action as possible. IS
This perfection, however, produces a cumbersome and complicated scale
that is often difficult for other workers to use. So, in this case,
the balance must be struck between perfection and undue complication.
Most of the problem appears to stem from the heterogeneity of the coastline. Perhaps the best option is to retain sensitivity by applying a specific exposure scale to the local area being, studied, and to limit the cumbersome complications by selecting a biological as opposed to a physical scale. Some objectivity may be retained in the biological exposure scale by using the numerical methods as pro- posed by Dalby et al (1978). Part II of this thesis describes how a biological exposure scale similar to that used by Dalby et al (1978) is developed for the Shetland Islands, and the limitations of this approach are considered.
It has already been indicated that direct physical measurement of wave action is essential to the proper understanding and confident use of the exposure scale. Part III of this thesis is devoted to an attempt to calibrate the Shetland biological exposure scale with measure' ments of wave pressures. An attempt to link quantitatively rocky shore ecology and wave action has already been made by Jones and Demetropoulos
(1968). They measured the dynamic forces of waves using a form of dynamometer (c.f. Stevenson, 1849), and related the maximum reading from this instrument to the height of various species above chart datum.
For a given species, one would expect, the topshore limit of its distribution and the maximum dynamometer reading to increase with exposure. The raising of intertidal zones as a response to exposure has been well documented by Burrows et al (1954) . The dynamometer developed by Jones and Demetropoulos consisted of a drogue attached to a spring balance, which itself was attached to the shore by means of a flexible coupling. The maximum "pull" of the waves was recorded 16
by an arm on the spring balance which remained in the extreme position
to which it was pushed by the balance pointer. While this simple
device appears to have produced some meaningful results, for the purpose
of the Shetland study, it was decided to employ a more flexible
electrical system that was capable of continuously recording various
components of wave action. It was thought that this would lead to
a wider appreciation of the wave forces acting on individual plants
and animals.
Most of this research project is concerned with the relationship
between wave exposure and the abundance of selected species expressed
through the exposure scale concept. Besides abundance, there are other measurable attributes of species which may be linked to wave exposure.
These are briefly considered in Part IV. PART II
THE SHETLAND EXPOSURE SCALE 17
CHAPTER 1.
Introduction
The biological exposure scale developed by Dalby et al (1978)
for Western Norway used raw data that are still being collected on
an annual basis for monitoring purposes. There is a similar rocky
shore monitoring programme being carried out in Shetland for SOTEAG
by the Oil Pollution Research Unit of the Field Studies Council (OPRU).
They have established about forty sites around the oil terminal at
Sullom Voe and their data are in a similar form that that used by
Dalby et al (1978) for the Norwegian exposure scale. It was thus
convenient to use their data in attempting to apply and modify the
Norwegian scale for use in Shetland. Bearing in mind these considerations,
it is understandable that the development of the Shetland exposure
scale closely followed a predestined path. However, it is appreciated
that the techniques used may not have been the best ones, and some
attempt has been made in this section to test other methods of
abundance measurement. Some attempt has also been made to study the
effect of selecting different criteria in the formation and use of
the exposure scale.
As previously mentioned, the confident use of the exposure scale
requires the effect of other physical variables besides wave action
to be minimised. This would involve selecting sites of hard bedrock with an even surface of moderate slope. Because the ideal can never be attained, it is important to study the tolerance limits of the
exposure scale to these other physical variables. As a method of estimating wave exposure, it is desirable that the exposure scale can
function over a wide range of shoreline types. Given that there is no change in the configuration of the coastline, it is also desirable that
the exposure grade assigned to a shore remains approximately constant
seasonally and from year to year. This is also tested in this section. 18
CHAPTER 1.
The Preparation of the Exposure Scale
2.1 Raw Data Collection
The first task was to decide which species were to be included on a biological recording sheet. It was soon discovered that certain species would be difficult to identify separately in the field, and so in many cases, these were lumped together as a single taxonomic unit. On the other hand, for some species it was considered useful to separately record subspecies and environmental forms. The final recording sheet was based on those used for Norway (Dalby et al, 1978) and Shetland (OPRU), and consisted of sixty taxonomic units corres- ponding to the most common plant and animal species likely to be en- countered. Nomenclature of the lichens follows James (1965), and the algae are as listed in Parke and Dixon (1976). Checklists for Shetland algae produced by Borgesen (1903) and Dixon (1963) were also useful.
Animal species recorded are all listed in the Plymouth Marine Fauna
(Marine Biological Assoc., 1957). Taxonomic units worthy of special comment are:
(i) Ceramtum and Catli^thanvvion species were aggregated into one taxonomic unit because initially it was decided that they would be difficult to separate in the field. They were mainly encountered growing together on mussel sheels on the more exposed shores. Later discussions with J.H. Price of the British Museum (Natural History) revealed that a more sensitive relationship with exposure was likely if the species were in fact separated.
(ii) Petalonia and Piunctaria species were also aggregated because of problems of identification. Laboratory examination revealed characteristics of each species on any one specimen.
(iii) Littorirux "saxatal-Cs". The taxonomic status of the rough 19
periwinkle appears to be in a rather confused state. James (1968)
classifies the various forms as being subspecies of L. saxatalis3
but Heller (1975) identifies them as four distinct species. In view
of the critical nature of Heller's specific characters, and some
uncertainty as to their universal applicability, for the purposes of
this study all forms of rough periwinkle are grouped as L. "saxatalis
Abundance data were collected from each site using the abundance
-scoring, belt-transect technique as devised by Crisp and Southward
(1958) and modified by Ballantine (1961) and Moyse and Nelson-Smith
(1963). When applied to Shetland, this involved selecting a 2-3 m. wide band of shoreline and marking stations with chalk at 0.2 m. vertical intervals up the band (approximately 1/10 tidal range). The vertical interval on the shore was measured by means of a cross-staff, as described by Nelson-Smith (1970). For the work in Shetland, a light- weight aluminium alloy cross-staff was designed (see Figure 2.1.1) such that it could be dismantled for easy carriage in aircraft. The hori- zontal pole has a spirit level bubble mounted in one end which can be viewed via an angled mirror by sighting through the middle of the pole. This allows the simultaneous view of the point further up the shore corresponding to the interval on the vertical pole. The horizontal pole can be clamped at various marked intervals up the vertical pole, depending on the vertical interval required between stations. For transport, it may be clamped parallel to the vertical pole. The cross-staff was usually set for a vertical interval of 0.2 m., but for very exposed shores where the zones are greatly uplifted and extended, 1 m. vertical intervals were used. Also, for working on very exposed shores, a rope and harness were often used as a personal safety precaution. In all cases, stations were marked between the low water spring tide level and the grey-green lichen zone, just 20
Mirror A! Line of Sight
Spiri*"t LeveT l
Scale i 1 cb. » 10 cm.
End View of Sighting Pole Knurled Knob
A A
Not to Scale
Figure 2.1,1 The Cross-staff 21
below the first flowering plants. Each transect would thus contain
about 10 to 20 stations. The top station was marked with either at
concrete pat with a nail in the top, or a painted yellow 'T* - the
horizontal bar representing the level of the top station, and the
vertical bar showing the direction of the transect down the shore.
As an aid in relocating the transect, the horizontal distance from
the top station to each station downwards was recorded with a tape measure. General site location data for each transect in the form
of a Grid Reference, compass bearing along the transect, maps and photographs along the transect comprised a site location sheet of which an example is given as Figure 2.1.2.
At each station on the transect, an area defined by the belt- transect width and +0.5 vertical interval above and -0.5 vertical interval below each station was assessed for abundance measurements.
Within this area, the abundance of any species present on the re- cording sheet was assessed according to the abundance categories listed by Dalby et al (1978) and given as Appendix 1. An example of a completed recording sheet is given as Figure 2.1.3. For the numerical handling of the data, each category of the abundance scale was given a number as follows: Ex 7, S 6, A5, C 4, F 3, 02, R 1.
OPRU have been using a very similar method for the collection of biological data for monitoring purposes. Although their precise abundance scoring technique has been modified from year to year
(Baker et al., 1976; Baker et al., 1977; Hiscock et al., 1978;
Hiscock et al., 1979), it is basically similar to that described above, although some criteria might be slightly different. Forty
OPRU sites around Sullom Voe were used in the exposure studies. In addition, a further forty-three sites were selected from around North
Mainland, Shetland, in order to have sites representative of the 22
SITE LOCATION DATA SH18 Burravoe, Yell (SH18) Grid Ref : HU 530 798 Bearing s 198°
1 •i
eoga Ness
Muckle0 Skerr y of Neapaback
Figure 2,1.2 Example of Site Location Sheet.
Figure 2,1.4 Location of Sites in Shetland 25 Whole Shetland Shetland Unit Norwegia n Exp. Exp. Exp. Exp. Grade Gra.de .Site Name Grid Ref, Grade Grade let Run Final MG1 Mavis Grind HU344690 5 5.25 5.25 4.75 • MG2 Uavis Grind HU341685 6 5.25 5.25 4.75 MG3 Mavis Grind HU339684 8 5.75 5.75 5.75 MG4 Mavis Grind . HU337683 8 7.75 7.50 7.50 MG 5 Mavis Grind HU333684 8 8.00 7.75 7.50 MG6 Mavis Grind HU333683 5 4.50 4.50 4.50 MG7 Mavis Grind HU333683 3 3.25 3.50 3.50 UG 8 Mavis.Grind HU332683 2 3.00 2.00 2.00 MG9 Mavis Grind HU332683 2 1.75 1.75 1.75 MGIO Mavis Grind HU331683 1 1.75 0.75 0.50 MG11 Maris Grind HU326688 0 1.00 0.00 o.oo SH12 Mangaster Vest HU333698 6 5.75 5.75 5.75 SH13 Mangaster North HU327705 2 2.75 2.00 2.00 SH14 Grind of the Navir HU212805 0 1.00 0.00 O.OO SH15 Whalwick Taing HU236810 1 1.75 0.75 0.50 SHI 6 Ronas Voe HU279823 2 2.75 1.75 1.75 SH17 Morth Roe HU367894 7 6.75 6.25 6.00 SH18 Burravoe, Yell HU530798 8 8.00 8.00 7.75 SH19 Grut Wick HU506706 1 1.75 1.00 l.OO SH20 Dury Voe HU457627 3 2.75 3.00 2.75 SH21 Saltayre HU471519 6 6.50 6.25 6.00 SH22 Gletness East HU478520 1 2.00 1.50 1.50 SH23 Gletness Vest HU478520 5 5.25 5.25 5.25 SH24 Freester HU454530 5 4.75 4.50 4.50 SH25 Bridgend, East Burra HU373331 7 8.00 8.25 8.50 SH26 Whiteness East HU381421 5 4.50 5.00 5.00 SH27 Vhiteness Vest HU380419 - 2.50 3.00 2.75 SH28 Vesterwick HU273430 0 1.00 0.00 O.OO SH29 Burrastow HU224475 3 2.75 3.00 3.00 SH30 Sandness HU1B6562 0 1.00 0.00 O.OO SH31 The Vadils, South HU289549 9 9.00 9.00 9 .00 SH32 The Vadils, North HU289552 9 8.00 9.00 9.00 SH33 Mo Vick HU297564 8 8.00 8.25 8.25 SH34 Clousta HU304570 8 8.00 8.25 8.25 SH35 Vementry HU308598 7 8.00 7.75 7.75 SH36 Stead of Aithsness HU322593 5 5.25 5.25 5.25 SH37 Aith Voe v HU351574 7 7.00 7.00 7.DO SH38 Voe HU405635 8 8.00 7.50 7.75 SH39 Voe Mobile HU405635 - 6.00 7.25 7.75 SH40 Clubb of Mulla HU393648 5 4.50 4.75 4.75 SH41 Bust a HU346664 7 6.75 6.50 6.50 SH42 Swarbacks Minn HU327626 2 2.50 2.25 2.50 SH43 Otter Ayre HU326668 2 2.25 1.75 1.75 0P44 Nibon HU303732 4 4.75 4.50 4.50 0P45 Hillswick HU277770 3 2.75 . 2.50 2.50 0P46 Eshaness HU208789 0 1.00 0.50 0.50 0P47 Ness of Housetter HU362839 4 3.50 3.75 3.75 0P48 Olas Ness HU353831 5 4.50 4.50 4.50 OP49 Saberstone HU372811 2 2.00 1.50 1.50 0P50 Ollaberry, East Ness HU366800 3 3.25 3.00 3.00 OP51 Grunn Taing HU379790 5 5.00 4.25 4.25 OP52 Gluss Island East HU378776 3 2.75 3.00 3.00
Table 2.1.1 Site Locations and Exposure Grades 26
Whole Shetland Shetland Unit Norwegian Exp. Exp, Exp. Exp. Grade Grade Site Name Grid Ref. Grade Grade. 1st Run Final 0P53 Glu8s Ayre HU370772 6 5.75 6.50 6.75 0P54 Noust of Burraland HU373751 4 3.75 4.00 4.00 0P55 Fugla Ayre HU374742 - 4.25 8.50 9.00 0P56 Sullom Pier HU363736 6 5.50 7.75 7.75 OP 57 Mavis Grind East HU344690 6 6.00 6.75 6.75 0P58 Voxter Ness HU361701 4 4.00 4.50 4.75 0P59 Runway, Scatsta HU380731 6 6.00 5.75 5.75 0P60 Voe of Scatsta HU398733 - 5.50 7.25 7.50 0P61 Construction Jetty HU393750 6 5.75 6.75 7.00 0P62 Vats Houllands HU383761 5 5.00 5.25 5.00 0P63 The Karnes HU384765 4 4.00 4.50 4.50 0P64 Brei Wick HU392769 4 4.25 4.25 4.25 0P65 Roe Clett HU394781 3 2.75 2.75 2.75 0P66 South of Scaw Taing HU396782 4 4.75 4.50 4.50 0P67 Scaw Taing HU397783 2 2.50 2.50 2.50 0P68 Between Scaw and Swarta Taing HU398783 4 3.50 3.50 3.50 0P69 Swarta Taing HU401782 4 5.00 4.25 4.25 0P70 South of Swarta TaingHU401780 4 3.50 3.50 3.75 0P71 Ay Wick HU412778 3 3.25 3.00 3.00 0P72 North of Ay Wick HU416783 3 3.50 3.00 3.25 0P73 West of Mioness HU418791 2 2.75 1.75 1.75 0P74 Mioness HU425792 3 2.75 3.00 3.00 0P75 Croo Taing HU432786 - 7.25 6.00 5.75 0P76 Fugla Ness HU439775 4 3.50 3.75 3.75 0P77 S. of Markna Geo HU449859 3 3.00 2.75 2.50 0P78 Geo S.W. of Clothan HU456808 3 3.00 2.75 2.50 0P79 Riven Noust HU507731 3 3.50 3.00 3.00 0P80 Vidlin Ness HU480662 4 3.75 4.50 4.25 0P81 Kirkabister HU486667 - 4.50 5.50 7.75 0P82 The Taing, Lunnaness HU493678 2 3.00 2.50 2.50 0P83 Scarfataing HU342638 5 4.50 4.75 4.75
Table 2.1.1 (cont) Site Locations and Exposure Grades 27
complete range of exposure. Eleven of these sites were situated near
Mavis Grind, North Mainland, where the configuration of the coastline has allowed an apparently large gradient of exposure over a short distance. This area was selected for special studies throughout the project. The sites were numbered as follows:
MG 1 - 11 : Mavis Grind sites selected myself
SH 12-43 : other Shetland sites, selected myself
OP 44-83 : sites selected by OPRU.
Their location is given in Figure 2.1.4, and their precise
Grid References may be found in Table 2.1.1.
2.2 Application of the Norwegian Scale
Initially, it was decided that the Norwegian scale should be applied directly to the data obtained from Shetland. As in the
Norwegian exposure grading technique, the maximum abundance score for each species at a particular site was extracted from the raw data.
In this way, a single value for the optimum performance of a particular species along a transect was obtained. Program MAVIS (see Fiche 1), written by D.H. Dalby, was used to extract the species' maximum scores from the raw data. Maximum scores for each transect recorded are given in Appendix 2. Stored on file, these maximum scores were then compared with the standard species abundances comprising the
Norwegian exposure scale, also stored on file. Program BALL 3 (Fiche 1), written by D.H. Dalby, was used for this purpose. For each site, a set of similarity coefficients corresponding to each grade of exposure was produced by summing the non-standardised Euclidean Distances for each species. The selected exposure grade for the site is the one with the highest similarity coefficient. The maximum abundance scores for the following species were used, since it was thought that these species 28
were present in similar quantities in Norway and Shetland:
Alaria esculenta Pelvetia canaliculata Ascophyllum nodosum Porphyra umbilicalis Codium fragile Palmaria palmata Corallina sp. Verrucaria mucosa Fucus serratus Balanus balanoides Fucus spiralis Gibbula cineraria Fucus vesiculosus f. vesiculosus Mytilus edulis Himanthalia elongata Patella sp. Laminaria digitata Pomatoceros triqueter Lichina confinis Spirorbis sp.
Bearing in mind that the Norwegian exposure scale ranges from Grade I
(exposed) to Grade 9 (sheltered), the exposure grades for the Shetland
sites were computed as given in Table 2.1.1.
On the whole, these exposure grades appeared to make sense from
an overall view of the expected relative exposure of the various sites.
However, there were some discrepancies, particularly noticeable at
the extreme ends of the exposure range, that were worthy of further
investigation.
At the exposed end of the range, an inspection of the relative
abundances of certain species revealed that many sites that were
aggregated into Grades 1 - 2 on the Norwegian scale could be differ-
entiated into three groups corresponding to the proposed Grades 0, 1, and
2. as discussed in Dalby et al (1978)-. Shores of the proposed Grade 0
type were found along the outer coast on the west side of Mainland,
Shetland, notably at sites SH14 and OP46 (Eshaness), SH30 (Sandness),
MG11 (Mavis Grind) and SH28 (Westerwick). It is highly likely that
Grade 0 shores do in fact exist in Norway, although none were included
in the preparation of the Norwegian scale. Grade 0 shores, as recognised here, are backed by high cliffs (around 30 m. high) and
so probably have deep water close inshore, and face the unimpeded
expanse of the Atlantic Ocean. The lower shore Is dominated by large
quantities of Mytilus edulis and Alaria esoulentaj and above this and
intermingling with it is a fringe of Ceramium and Callithamnion.
There are also a few barnacles and limpets present, together with a
band of Porphyra umbiliaalis and a higher band of Porphyra linearis.
The black lichen zone extends up to 30 m. on the cliff. The most
exposed site that was visited in Shetland must undoubtedly be at
the Grind of the Navir, Eshaness (SH14).
Grade 1 sites were chosen as those present in slightly less exposed locations on the outer western coasts, and also encountered on the eastern side of Mainland, Shetland where they are subjected to the shorter fetch across the North Sea. In this case, the shoreline community is dominated by Mutilus edulis and Balanus balanoides on
the lower shore. Patella vulgaba is also extremely abundant, while the abundance of Alariay Ceramivm3 Callithamnion, and Porphyra is
similar to that recorded on Grade O shores. Grade 1 shores are backed by low cliffs, and examples may be found at SH19 (Grut Wick) and
SH22 (Gletness) on the eastern side of Mainland, Shetland.
At the sheltered end of the exposure range, using the Norwegian scale, a large number of Shetland shores were grouped in Grade 8, while physical and biological evidence indicate that they represent a gradient of exposure such that they should be redistributed into
Grades 7-9. All of these shores are dominated by Asoophyllwn nodosum and are to be found at the head end of sheltered voes. Large quantities of Littorina littoralis are almost always present amongst the Ascophyltm but Littorina littorea appears in large quantities only on shores that 30
appear to be slightly more exposed. These shores were assigned to
Grade 7. As recognised here, Grade 8 shores, besides being in more
sheltered locations, typically have a more•extensive understorey of
such species as Gelidium pusiHum3 and large individuals of Mytilus
edulis are often found.
Sheltered rocky shores, assigned to the Grade 7 and Grade 8
categories by the Norwegian scale, are commonly found at the head
end of voes in Shetland where the maximum fetch is no more than 1 km.
More sheltered shores are not as common as they are in the Fensfjord
area of Norway, although the area called The Vadils of Brindister Voe
near Sandness (around SH31 and SH32) has an extremely involuted
shoreline, and sites with a very small maximum fetch may be found.
In this area, site SH31 was assessed as a Grade 9 shore using the
Norwegian scale. The distinctive biological community of this site
and an adjacent site (SH32) indicated that both could perhaps be
justifiably classified as Grade 9 shores.
Some doubt in the validity of applying the Norwegian scale directly
to the Shetland sites arose partly from the fact that more exposed
sites were encountered in Shetland, and partly from consideration
of the differences in the community composition of shores between the
Fensfjord area of Norway and Shetland. Whether or not particular
species were to be used in the exposure grading process, it was
considered important to appreciate the differences in their distribution.
Fueus distiahus subsp anoeps may be found in considerable quantities
at the more exposed locations in Norway, and indeed, Dalby et al (1978) predict that it may occur over the exposure range Grade 0 - Grade 2.
On Norwegian shores, it is present in the same niche that would be
occupied by Ceramium and Callithccrmion in Shetland. The latter two 31
species do occur around Fensfjord, but are less common. In Shetland,
F. distiohus subsp anceps was found only at two locations, SH14 (Grind of the Navir) and SH30 (Sandness), and then only in small quantities.
Powell (1963a) has mapped the occurrence of this subspecies in the
North Atlantic area, and he has drawn attention to its sparse pop- ulation in Shetland (Powell, 1963b). He recorded F. distiohus anaeps from two sites at Sandness (Matta Taing and Quilva Taing) and from one site north of Eshaness (Villians of Hamnavoe). The occurrence at the Grind of the Navir is about 4 km. south west of the Villians of Hamnavoe. It appears to be the case that in Shetland the populations of F. distiohus anoeps are relics of an earlier distribution, now at the limits of its geographical range, and moreover it occurs only sporadically and unpredictably at Grade 0 locations.
A most striking difference between Norwegian and Shetland shores is that the latter are dominated by a greater abundance of Mytilus edulis than the former. In Shetland it is common to find over 50% of the lower region of exposed shores covered by mussels. In contrast,
Palmaria palmata is present in smaller quantities in Shetland than in Norway, and is generally rare unless it occurs epiphytically on the stipes of laminarians.
Codvum fragile occurs predictably in Norway in areas of shelter at extreme low water. Its distribution in Shetland is more sporadic, as it is not always present in positions of extreme shelter. In fact the only large population of C. fragile that I have found in Shetland
(1980) is in Culsetter Voe, situated to the west of Mavis Grind. Jones
(1974) traces the spread of Codium fragile into the North Atlantic.
It appears to have spread from the north, having established itself in Norway (1918) before the north'of Scotland (1957). Dixon (1963) 32
records its presence in Shetland, but not in Culsetter Voe. Codium fragile is, therefore, a pioneer species in the Shetland Isles and so cannot be used reliably to indicate sheltered conditions as it probably has not yet reached its maximum distribution. On the other hand, Laminaria saooharina was not recorded in large quantities from the Fensfjord area of Norway, whereas the broad-fronded form (Irvine,
1974) is fairly common in sheltered waters in Shetland. It is also a useful indicator of sheltered conditions.
In seeking reliable exposure indicator species, the "free-living" forms of AscophyZlum nodosum and Fucus serratus were very useful in the Norwegian study. However, the search of long stretches of Shetland coastline revealed that in this area these environmental forms are extremely rare and probably required a reduction in salinity for their development. Over the whole of Shetland, the free-living form of
A, nodosum known as eaad maokaii (Gibb, 1957) has been found at only one location (The Briggs, Vementary), although strands of apparently
"free-living" A. nodosum have been found elsewhere. These strands are lighter in colour than the attached form and are also more branched.
With some individuals, the branches extrude from a tangled mat of tissue resembling a holdfast. Often, this holdfast area is more defined, and a small stone may be trapped inside. Unattached and living forms of F. serratus usually have their holdfast formed around a small stone.
Often the plant is merely a dismembered fragment of a larger plant, and in this case the broken end of the frond appears to be congealed.
The fronds of these individuals are much serrated and curled in a similar way to F. serratus f. grandifronds Kjellm.
These apparently "free-living" forms of A. nodosum and F. serratus are found in sheltered locations, and usually where there is also a 33 Cullivee, Yell (HP 544 025) The Vadlla (HtJ 290 550)
10 OCT 79 Road
11 OCT 79 Free living strands of Ascophyllum nodosum Free living strands of Fucus serratus A. nodosum ecad mackaii Figures are salinities in parts per thousand The Briggs, Vementary ; (HU 310 584)
Brig of the Voe (HU 356 844)
11 OCT 79
Figure 2.2.1 The Distribution of "Free-Living" Fucoids in Relation to Salinity 34
substantial dilution of seawater. The occurrence of these forms in Shetland, together with accompanying salinities are summarised in Figure 2.2.1. It seems likely that a reduction in salinity is required before the structure of the attached plant changes to give rise to free-living fragments (Gibb, 1957). An involuted coastline will aid this development, and it will also produce an area sheltered from wave action. However, it seems unlikely that the shelter from wave action is a necessary pre-requisite for the formation of free- living algae. This point is illustrated by the situation at Brig of the Voe, north Mainland, where strands of free-living A, nodosum have been found where a large stream, Roer Water, enters Collafirth
Voe. A salinity sample was taken from amongst the Asoophytlum and it revealed that the water here was almost fresh (salinity l°/oo).
Site OP47 (Ness of Housetter) , which is only 800 m. from this point and only slightly more exposed, has an exposure grade of 3.75, in- dicating that this area is indeed not an extremely sheltered site.
Bearing in mind the floral and faunal differences between Norwegian and Shetland shores, it was decided to redefine the Norwegian exposure scale in order to form one that is more appropriate to Shetland.
2.3 Formation of the Shetland Scale
The first step in the formation of the new Shetland exposure scale was to put each of the sites into an exposure category from
0 - 9 as proposed above. The initial ranking of the sites was aided by a Correspondence Analysis (Reciprocal Averaging, Hill, 1973) using the maximum abundance score for each species at each site as attributes.
This produced ordinations for the 60 species and 83 sites. The two major axes of variation for the species ordination an,d the site ordination are shown plotted in Figures 2.3.1 and 2.3.2 respectively. Axis 1 of Axis 1 35
100 \FUCU5 90 aorratuo .'-Furcellaria "free"
80
70 • •
60
50 •
40
30
20 f»
10> ••-Porphyra linearis .Fucus distichus * i * • • . 10 20 30 40 50 60 70 80 90 100 Axis 2 Figure 2,3,1 Reciprocal Averaging - Species Coordinates
Axis 100
90 • m The Vadils • • »
80
70
60 .S < ' * # • .
50
0 40 9 *
30
• V* • 20f
10 ^Sandness . ' it—Grj.nd of Narir 10 20 30 40 50 60 70 80 90 100 Axis 2 Figure 2,3,2 Reciprocal Averaging - Site Coordinates the species ordination is directly comparable to Axis 1 of the site
ordination, and it is clear that Axis 1 is related to wave exposure.
Species such as Asoophyllum nodosum and Laminaria saoaharina that are
typical of sheltered conditions appear at the top of Axis 1, as do the
sites that are in the most sheltered locations. It is interesting to
note that the two sites at the top of Axis 1 are both in The Vadils
(SH31 and SH32), one of which was given the exposure grade of 9.00 by
the Norwegian scale. Other sheltered sites appear further down the
axis, and this reinforces the view that these two sites are biologically
distinct from the others and should properly be called Grade 9 sites.
At the other end of Axis 1, there are sjpecies such as F. distiohus anoeps
and Porphyra linearis that are indicative of exposed conditions. On
the site ordination, the bottom of Axis 1 is occupied by the extremely
exposed sites referred to as Grade 0, notably Grind of the Navir (SH14)
and Sandness (SH30).
While it was clear that Axis 1 of the ordinations corresponded to
the wave exposure gradient, it was considered useful to try to relate
this estimate derived from biological data to some physical estimate
of wave exposure. Since the size of wind-driven waves arriving at a
shoreline are related to the distance to the opposite shore; the fetch
perpendicular to the shore and the maximum fetch to the shore were measured from maps for each site. As with all physical estimates of
wave exposure, it was soon realised that there were complicating factors.
Wave refraction would lessen the exposure of a site at the back of a
bay even though it might have the same fetch as a nearby site on a
headland. Because of this it was decided to modify the maximum fetch
by a coefficient related to the angle subtended by the sea horizon
at the site. In addition, it was discovered that a site on the inner
coast might have a short maximum fetch, but be close enough to the outer coast to be influenced by swell. A further coefficient was required. The final formula for the modified maximum fetch was:
Modified Max Fetch = Max Fetch X (A/180)* X (C/B+C)
A Angle subtended by sea horizon (°) B Distance to outer coast (km) C Minimum width of channel to outer coast (km) * . . only included if there is a sea horizon present.
Using a program written by P.W. Mueller (Imperial College),
Axis 1 of the Correspondence Analysis site ordination was plotted against the logarithm of the Modified Maximum Fetch for each site as shown in Figure 2.3.3. Although both parameters are merely estimates of wave exposure, it can be seen that there is a close relationship between the physical estimate of wave exposure and the biological estimate, as described by a quadratic regression. The correlation coefficient is -0.839, which is highly significant for 83 sites. (P = O.OOl)
The position of individual sites on the scattergram was later used in a consideration of their true position on the biological exposure scale.
In order to be able to readjust the Norwegian exposure grades to render them more appropriate to Shetland, it was decided to relate
Axis 1 of the site ordination to the Norwegian exposure grades of each of the sites. The two variables have a correlation coefficient (r) of 0.954 which for 83 sites is highly significant at P = 0.001. A plot of Axis 1 against Norwegian exposure grade is shown in Figure 2.3.4 with a linear regression fitted through the points. (Y = 11.14 X - 0.98).
The regression line was divided into intervals corresponding to each whole unit of exposure, and horizontal lines were drawn across the graph at these points. The sites falling in between these horizontal lines were then placed in the appropriate whole unit QUADREG
Figure 2.3.3 Modified Maximum Fetch vs. Axis 1 of Reciprocal Averaging
38 39
Axis 1 of Reciprocal Averaging Site Coordinates Y a 11.14X- 0. 98 100
Exposure Grade on Norwegian Scale
Figure 2.3.4 Axis 1 of Reciprocal Averaging vs. Norwegian Exposure Grade. exposure grade. Any marginal sites that appeared to be placed in the "wrong" exposure grade were reallocated using various aids.
My own subjective recollection of the physical exposure status of a particular site was used in conjunction with a consideration of its position in the Modified Maximum Fetch Scattergram (Figure 2.3.3).
In addition, an overall consideration of the maximum abundance of certain indicator species assisted with the reallocation of sites difficult to place on the scale. Sites where the biology on the shore was obviously influenced by a variable other than wave action were eliminated from the study at this stage.
The whole unit exposure grades of those sites that were used in the formation of the Shetland exposure scale are given in Table 2.1.1.
SH27 (Whiteness West) and OP75 (Croo Taing) were omitted because it seemed that on these shores there was a change in wave exposure up the transect. SH39 (Voe Mobile), 0P55 (Fugla Ayre), 0P60 (Voe of
Scatsta) and 0P81 (Kirkabister) were not included because the shores were made up of very small boulders which supported a reduced flora and fauna, presumably because of the mobility of the substrate.
Having put each of the sites into a whole unit exposure grade from Grade 0 to Grade 9, the next stage was to calculate typical abundances of species for each grade of exposure. Program BALL 2
(written by D.H. Dalby and listed in Fiche 1) was employed to calculate the mean maximum abundance score for each species for each grade of exposure. For example, five sites were assigned to Grade 0. The abundance value calculated by BALL 2 for limpets for Grade 0 would be the mean of the maximum scores obtained for limpets for those five sites. Using program BALL 2A (written by D.H. Dalby and listed in
Fiche 1) the mean maximum abundance value was plotted against exposure grade for each species. A smooth polynomial curve was then fitted through the data points such that the abundance of each specics at i units of exposure grade could be interpolated. For many species, this produced unimodal curves that showed the abundance of the individual species responding neatly to the exposure gradient defined by the scale. Not all species showed a neat variation in abundance with exposure, and an examination of the abundance curves allowed the selection of certain species that would be disregarded in further analysis. The following taxonomic units were eliminated because their abundance scores changed little over the range of exposure:
Grimmia maritima Ulva lactuca Bamalina sp Enteromorpha sp Grey green lichens Cladophora rupestris Orange red lichens Littorina "saxatalis" agg. Verrucaria maura Halichondria panicea HiIdenbrandia prototypus
The following species were recorded too infrequently to be used reliably as indicators of exposure or shelter:
Laminaria hyperborea Actinia spp. Catanella repens Fucus serratus free Lomentaria articulata Halidrys siliquosa Codium fragile Fucus distichus subsp anceps Laurencia hybrida Furcellaria fastigiata
Similarly the following were disregarded because they occurred only at certain times of the year:
Dumontia incrassata Scytosiphon lomentaria Bangia fuscopurpurea Petalonia/Punctaria
Nucella lapillus was not used because its abundance on exposed shores seemed to be related to the occurrence of suitably sheltered crevices, and Chorda filum was likewise excluded because it depended on the occurrence of a soft lower shore. This left the following species as useful indicators of the wave exposure gradient:
Verrucaria mucosa Palmaria palmata Lichina confinis Corallina officinalis Pelvetia canaliculata Laurencia pinnatifida Fuous spiral-is Balanus balanoides Fuous vesiculosis Littorina littorea Fuous serratus Littorina littoralis Himanthalia elongata Gibbula cineraria Asoophyllum nodosum Patella vulgata Laminaria digitata Mytilus edulis Laminaria saccharina Spirorbis spp. Alaria esculenta Pomatoceros triqueter Lithothamnia Gelidium pusillum Porphyra umbilioalis Fucus vesiculosus f. linearis Gigartina stellata Ectocarpus sp. Chondrus orispus Porphyra linearis Ceramium/Ca I li tharrmion
The abundance of each species at \ units of exposure grade, produced from the abundance curves, forms the standard set of species abundances with which any new site may be compared. Indeed, the original data may be compared with these standards using BALL 3 in order to provide exposure grades to a precision of \ unit of exposure. These exposure grades are given in Table 2.1.1.
It is clear that these new estimates of the exposure grade of each site may themselves be used at the beginning of the process to produce further smoothing and perhaps more precision. This idea is diagrammatically illustrated in Figure 2.3.5. The mean maximum abundance scores of each species were produced at | unit exposure grade intervals by re-running BALL 2 with the new exposure grade estimates. These were plotted by BALL 2A and new polynomial curves fitted to the data. Examples of these curves are given in Figures
2.3.6 and 2.3.7, while the complete set of abundance curves are in
Fiche 2. From the abundance curves, the new standard set of species Haw Data
Prog MAVIS J MAX Maximum Abundance Scores DATA 3
BALL 2 requires exposure grades and MAX BALL 3 requires MAX and DATA 3
Figure 2.3.5 Diagram of Exposure Scale Programs it i IK.i'*. vi MI i>c rv,i\ •VII T. I . I' l.V 4.;". 4.mi A.-r, o.oo •..mi «,./•. r,.::j !,., '• r>.'.n t,. t>, /.vi • •/.: >. /.".• >./'• it.cn «.." y.i.'i J.-V 4.o>i 'J.K '..-ii 'J.'JII 'j.r'J.III 'j.i'o 4.
4.n b.^i
\A fL'OJ^ VLMCULOM'O o
7
* * * 0 *0 0* * 0 XXX
• *0 0 T. T x x—x—x—x—x—x—x—x—x—0 x
A 5 EXPOSURE GRADES
ORDER Cr POLYNOMIAL = A
17 ASCCPHYLLUM NODOSUM -.25 0 .25 .50 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 00000 0 0000000000 .27 0 4.25 4.50 4.75 5.00 5.25 5.50 5.75 £.03 6.25 6.50 6.75 7.00 7.25 7.50 7.75 8.00 0.25 8.50 0 . 07 . 58 1.25 2.01 2.B1 3.59 *.33 4.98 5.53 5.97 6.28 6.46 6.55 6.54 6.47 6.38 6.32 8.75 9.00 9.25 6.33 6.49 6.64
17 ASCOPHYLLUM NODOSUM
X X X X X • x 0 0 o * x 0 0
4 5 EXPOSURE GRADES ORDER OF POLYNOMIAL = 4
Figure 2.3.6 Abundance Curves of Fucus Vesiculosus and ABcophyllum nodosun ;>1 m nuiii ( vr pi r nil o ..». . /., 1.(0 i.; . !.'.') ?.»n ;>.'.II ,'./'.• •».'•'•• 'i. >'• ,.t / s.ni t..i.' i,.)'- 'i.'i/ 'i.i.i 'j.h -i. t.. • i.i'-i n.i-t r. M t, i'.ni I.H: J.-vi i.e.1 .M
i.M) "1.70 •».()') ').''• i <••>"• I'-'-'i) b-i'j 7.01) /.;<•> ;.••;] /./'» ti.iti ti., .-.•i, .;•() .i'. u o- o n o o n o o n n o (j o.7v o.uri 0.20 ooo 21 ftLnRinESCULENT O
0 0 0 0 B NU 5 flD M 4 C E
S 3 C LA E 2
* x x * -X X X X X X-
4 5 0 1 EXPOSURE GRADES
ORDER Of POLYNOMIAL = 4
43 MrTILUS EDULIS — .25 0 .25 .50 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 5.71 5.93 6.16 6.27 6.20 6.06 5.36 5.62 5.35 5.05 4.74 4.43 4.12 3.82 3.53 3.26 3.02 4.25 4.50 4.75 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50 7.75 8.00 8.25 2.61 2.52 2.46 2.23 2.16 2.11 2.08 2.06 2.06 2.06 2.05 2.03 1.99 1.91 1.79 1.62 1.37 8.75 9.00 9.25 1.04 0 0
43 MTTILUS EDULIS
X 0X *0 * * 0 0
0 * 0 0 x * 0 0 0 0 x x XX Q x x x oxxxxxxxo * 0 0 0 0
4 5 EXPOSURE GRADES
ORDER Of POLYNOMIAL
Figure 2.3.7 Abundance Curves of Alaria esculenta and Mytilus edulis Exposure Grade Specie3 0 1 2 3 4 5 6 7 8 9
Vorrucaria mucosa O-F F-C C-A C-A C-A A A-S A-S On . A-S Lichina confinis F-C 0 R-0 R-0 R-0 R-0 R-0 R R R-0 Pelvetia canaliculata R-0 ' F F-C F-C F-C C C-A Fucus spiralis R R-0 0 O-F I F F O-J Fucus vesiculosus 0 C-A A-S C-A F A-S Fucus serratua F A S S A C-A S Himanthalia elongata R-0 O-F O-F O-F 0 R-0 Ascophyllum nodosum R-0 C-A S-Ex S-Ex S-Ex Laminaria digitata F A S s S A R-0 Laminaria saccharina R R O-F F-C F R-0 Alaria esculenta A S C 0 R R Lithothamnia S s S s S-Ex S-Ex S-Ex S .C-A R Porphyra umbilicalis S C-A F 0 0 0 R Gigartina stellata F F-C C A A A C F R-0 Chondrus crispus R R-0 R-0 0 O-F F-C F-C 0 Ceramium/Callithamnion F-C F-C F O-F O-F O-F 0 0 R-0 R Polysiphonia lanosa R R-0 0 0 O-F F-C F-C R Palmaria palmata O-F O-F R-0 R R R Corallina officinalis F F F-C F-C F-C F-C F-C O-F R Laurencia pinnatifida 0 C C F-C F 0 R Balanus balanoides F-C A A-S A C F-C F 0 R-0 Littorina littorea R O-F C A-S A-S C R Littorina littoralis R R-0 0 F-C A S S-Ex S-Ex S Gibbula cineraria R R-0 F C F R-0 Patella vulgata C S S-Ex S-Ex S S A-S C-A F Mytilus edulis S S A-S C F O-F 0 0 0 Spirorbis R-0 F C C-A C-A C C F-C Pomatoceros triqueter R R R R R-0 0 O-F F 0 F. vesiculosus linearis R R R Gelidium pusilium R-0 F-C S Ectocarpus R c Porphyra linearis A F-C O-F R
The simplified version of the exposure scale has been extracted from DATA 3, The numerical equivalents of the descriptive terms are as follows; 0.01-1.24 Rare R 1.25-1.74 Rare to occasional R-0 1.75-2.24 Occasional 0 2.25-2.74 Occasional to frequent 0-F etc •
Table 2.3.1 Simplified Version of Shetland Exposure Scale .47
abundances comprise the exposure scale with which the original data may again be compared to provide final exposure grades (Table 2.1.1).
It is clear that the cyclic process could be continued, but in case the processing should behave unpredictably, it was stopped after the exposure grades had been reassessed once. The effect of further cycles was investigated later, as described in Section 3.3.
A listing of the set of standard species abundances which comprise the new Shetland exposure scale is given in Appendix 3. An abbreviated and simplified form of this is given in Table 2.3.1.
2.4 The Exposure Scale in Practice
Although the preparation of the exposure scale necessarily includes some subjective steps (eg. which species to be dropped), in application it is wholly objective. One test of its reality is that meaningful patterns emerge when exposure grades are compared with site positions.
Exposure grades for sites on the outer coast of Shetland are typically in the range Grade 0-2. Sites on the Atlantic west coast invariably have an exposure grade of Grade 0 unless the swell is impeded by offshore stacks or altered by irregularities in the coastline. In this case, the exposure grade may rise by up to a grade as is demonstrated by two adjacent sites (SH14 and 0P46) at
Eshaness. Offshore stacks cause 0P46 to have an exposure grade of
Grade 0.50 compared to Grade 0.00 at SH14. The effect of refraction is clearly seen at a number of sites, when the exposure grade at the back of a wide bay may rise to Grade 2.00, despite the fact that the site is open to a large sea horizon. An example of this is the situation at Mavis Grind described below. Sites* of maximum exposure on the eastern coastline of Shetland generally have an exposure grade 48
of around Grade 1.00 compared to sites on the western coast which are of Grade 0.00. This is presumably due to the shorter fetch across the North Sea on the eastern coast.
Typical exposure grades for sites on the inner coast range from Grade 5.00 to-Grade 8.00 depending on the size of the voe and the proximity of the site to the outer coast. These values are generally reached fairly rapidly on entering a voe from the open sea because the entrance to the voe is usually narrow and often obscured by islands. The only large area m Shetland with exposure grades in the range Grade 2.00 to Grade 5.00 is the Yell Sound / Sullom Voe region. Yell Sound is sufficiently wide to allow a gradual reduction in swell penetrating from the north and east, and a groundswell of a few centimetres can usually be observed around Calback Ness. In addition, the fetch within Yell Sound is sufficient to allow sizeable waves to develop during a local storm.
The effect of coastal configuration on exposure grade is more precisely illustrated by reference to a few small areas that have been studied in detail (see Figure 2.1.4).
The configuration of the coastline near Mavis Grind, North Main- land is such that there appears to be a large variation in wave exposure over a short distance. Initially the abundances of species were recorded along 11 transect sites (MG1 - MG11). These sites were used in the formation of the exposure scale, and were given precise grades by the technique described above. Later, additional sites
(MG2A, MG3A, MG5A, MG5B, MG6A, MG7A, MG7B, MG8A) were recorded as detailed in Appendix 2. Their exposure grades were found by comparing the species maximum scores with the exposure scale using BALL 3.
The exposure grades of all the sites at Mavis Grind are given in
Figure 2.4.1. Figure 2.4.1 Location of Sites and Exposure Grades around Mavis Grind is vO It can be seen that the exposure grading technique.appears to be very sensitive, as is seen by the gradual rise in exposure grade
(increasing shelter) that occurs towards the back of the bay on the
Atlantic side of the narrows (minn) to the west of Mavis Grind. Then follows a rapid but regular rise in shelter through the minn as is shown by the exposure grades of sites MG9 to MG6. Numerous visits to the area under different wind and wave conditions indicate that these exposure grades are valid and that the change in exposure grade is not abrupt due to the influence of swell from the Atlantic that decays through the minn as arcs of secondary waves. The influence of these secondary waves on exposure grade may be seen on the Holm of Culsetter and at the same radius from the minn on the north shore of the Voe of Culsetter. Away from the influence of the swell, the exposure grades of shores within the voe become very high (sheltered) due to the short fetches over which local winds may produce wind- driven waves. To the east of Mavis Grind, greater fetches produce more exposed conditions (lower exposure grades) although it is clear that swell does not penetrate to this end of Sullom Voe.
The influence of small amounts of swell on shoreline ecology and exposure grade is considerable. This is further illustrated by the situation at Whale Firth on the east side of Yell Sound.
J.A. Fowler and others from Leicester Polytechnic have been carrying out their own monitoring surveys in this area since 1978 (Fowler, 1978) and they have kindly allowed me to use their data. Since their data collection methods are similar to OPRU's and my own, it was a simple matter to produce exposure grades for their sites which are shown on a map in Figure 2.4.2. On visiting the area, it was apparent that swell from a northerly direction could penetrate far into the Figure 2.4.2 Location of Sites and Exposure Grades at Whale Firth, Yell and Gletness. firth decaying only gradually. This is reflected in the exposure
grades which only become high (sheltered) after a bend in the firth
at Gremista.
Another interesting area in Shetland from the point of view of
wave exposure is that around Gletness on the east Mainland coast.
A map of this area, together with the positions of sites and exposure
grades is given in Figure 2.4.2. SH22 faces the open expanse of
the North Sea, but the presence of small offshore islands appears
to be sufficient to make the site no more exposed than Grade 1.50.
The refraction of swell into the Voe of Gletness means that the
exposure grades of SH21 and SH23 are much higher (Grade 6.00 and
Grade 5.25 respectively). The difference of 0.75 of a grade of
exposure between these sites may be due to the shallower slope of
SH21 causing more sheltered conditions for a more luxuriant growth
of Ascophyllum nodosum. Local wind-driven waves will have a limited
effect because of the narrowness of the voe in relation to the maximum fetch which is over a small arc to the north-east. Catfirth
is a large bay into which swell may penetrate arid over which local winds may produce fairly large waves. The exposure grade of SH24
(Grade 4.50) reflects this. CHAPTER 3
A critical Assessment of the Exposure Grading Technique
It is clear that the exposure grades produced from the new
Shetland exposure scale faithfully reflect an observed impression of the wave exposure environment of an area. However, the techniques used to produce these exposure grades were not the only ones that could have been used, and thus it was considered useful to study the effects of alternative techniques and selection criteria.
3.1 Data Collection - Abundance Measurement
In the preparation and operation of the exposure scale, the abundance measurement methods used by OPRU and BP ecologists were adopted. For rocky shore monitoring purposes, these methods are useful in that they can be quickly used by relatively inexperienced people. This means that many sites may be assessed over a short period. However, the use of abundance scales tempts subjectivity, and the value of large categories of abundance assessed subjectively has been questioned.
The approach adopted by the Coastal Surveillance Unit (CSU) at the University College of North Wales in Bangor is rather different
(Jones et al., 1978). The abundances of species are recorded precise in 50 cm. X 50 cm. quadrats placed end to end down the shore. The point-frequency percentage cover of plants and numbers of animals are counted in each quadrat. This is a time-consuming process, but it does allow the abundances of species to be precisely measured on a narrow band of shore. For some monitoring purposes, the narrowness of the transect may be a disadvantage in that rare species may not be recorded. 54
A similar method is used in a rocky shore monitoring programme
carried out in Bantry Bay, Ireland, by members of University College,
Cork (Myers, Cross and Southgate, 1978). They adopt the same abundance
measurement method as the Coastal Surveillance Unit, although they
only select positions for their quadrats at fixed vertical intervals
on the shore. In this way, the time spent recording at the transect
site is reduced, while the precision of the CSU method is retained.
A disadvantage, however, is that the area of the shore that has been
investigated is further reduced.
The advantages and disadvantages of each method were discussed at
a "workshop" organised by D.H. Dalby and J. Baker. The findings of
the meeting have not been published to date, but they provided a useful
framework for this investigation.
In order to test the accuracy of the OPRU abundance scoring method,
eight transects in Shetland were chosen and recorded using the OPRU method and a modification of the CSU method. These were situated around
the headland to the west of Mavis Grind (MG6 - MG9) . In each case, only the station corresponding to the zone of maximum abundance for each species was selected for the abundance assessment. The stations along the transect were marked as fixed vertical intervals on the
shore as usual. For the modified CSU method, a 50 cm X 50 cm. quadrat was strung with five strings in each direction such that there were
36 sub-divisions in the quadrat with 25 intersections. For any particular species, the quadrat was laid side to side four times across the station of maximum abundance, thereby covering an area of 2 m. X 0.5 m.
Lichens and algae were assessed by counting the total number of inter- sections covering each species. Since there were 100 intersections in total, this gave a % frequency figure corresponding to a % cover. Animals such as the larger periwinkles, limpets and dogwhelks were 2 simply counted in each quadrat to give a total figure of organisms / m
n u Smaller animals such as barnacles, small Littorina saxatal'is 3 and
mussels were counted in a representative sub-division of each quadrat
and multiplied by the number of sub-divisions in the quadrat that
could be imagined as having that density. Spivovbis sp. density
was estimated in a similar way although the counting area was a
1X1 cm. square which was multiplied out. A % cover estimate was
also taken for barnacles and mussels.
In order to apply this data to the exposure scale, conversion to
OPRU style abundance categories was required. In most cases, this was
a simple matter of following the abundance guidelines for each scale.
However, subjective portions of the abundance scales for algae and mussels needed modification as follows:
Algae Mussels Ex More than 90% cover More than 80% cover S 60 - 90% cover 50 - 80% cover A 30 - 59% cover 20 - 49% cover C 5 - 29% cover 5 - 19% cover F 2-4% cover 1-4% cover 0 1% cover Small individuals present, but not under intersections. R Present but not under Only 1 or 2 large individuals. intersections. It was not considered necessary to alter the lichen scale since the maximum abundance of each lichen species never fell into the subjective portion of the scale.
The abundances of species obtained using the modified CSU method and the OPRU method are given in Table 3.1.1. The OPRU conversions of the CSU abundances are also given. The exposure grades calculated from the OPRU method and the OPRU conversion of the CSU method (termed 56 Col 1 : OPRU Abundance Estimate (Max) Col 2 i CSU Estimate (Max); % covcr for Plants and Mytilun; No./m^ for Col 3 t OPRU conversion of CSU animals
MG6 MG6A MG7 MG7A Species 1 2 3 1 2 3 1 2 3 1 2 3
Grimmia. maritime 0 P R 0 f R ------Ramalina F 4 C F 7 C 0 1 C 0 P R Grey Green Lichens S 16 C A 24 A A 26 A S 72 S Orange Red Lichens A 23 A C 9 C C 22 A A 40 A Verrucaria maura Ex 95 Ex S 93 Ex Ex 98 Ex Ex 95 Ex Verrucaria mucosa. S 62 S C 13 C A C c 6 0 Lichina confinis - - - F P R - - - - - Hildenbrandia 0 P R 0 P R 0 P R 0 P R
Ulva lactuca R P R „ — _ R P R 0 P R - Enteromorpha - - - - - 0 P R - - - Cladophora F 9 C F 3 F F 12 C F 3 F Pelvetia canaliculate F 13 C R P R F 2 F 0 P R Fucus spiralis F 3 F R 1 0 R P R - - - Fucus vesiculosus C 39 A 0 10 C ------Fucus serratus A 63 S A 42 A C 38 A 0 3 F ml rnm - Himanthalia elongate - - - F 1 0 - - - — Ascophyllum nodosum - - — — ------Laminaria digitata C 73 s A 77 S C 82 S s 96 Ex: Laminaria saccharine - - - - — — R 1 0 - - - — Laminaria hyperborea ------Alaria esculenta — — — * R 2 F R P R Lithothamnia C 15 C C 7 C S 40 A A 50 S Porphyra umbilicalis 0 P R R P R 0 1 0 0 1 0 Gigartina stellate S 48 A A 48 A S 59 A c 16 c Chondrus crispus - - - — - - - - - — Catanella repens - - - - — — ------Ceramium/Callithamnion 0 P R 0 P R 0 P R F 8 c Polysiphonia lanosa - - - — — — — - - - - — Lomentaria articulate 0 P R 0 1 0 0 P R - - mm Dumontia incrassata 0 P R - — — R P R - - - Codium fragile - - - - — — R P R - - - Palmaria palmata - - - — — ------— Corallina officinalis F 4 F F 3 F F 5 C 0 1 0 Laurencia hybrida ------Laurencia pinnatifida F 3 F C 16 C F 15 C 0 2 F
Balanus balanoides F 2816 F A 12120 A A 14760 c s 14140 A Littorina "saxatalis" S 376 S S 6480 C Ex 5400 F S 1750 C Littorina littorea R 3 F 0 1 F 0 1 F - - - Littorina littoralis C 9 F F 2 F c 11 C - - - Gibbula cineraria ------Patella S 210 Ex A 118 S A 133 s Ex 295 Ex Nucella lapillus A 22 A A 14 A C 10 c A 26 A Mytilus edulis 0 0 0 0 2 F A 0 0 F 8 c Spirorbio C 7100 0 F 4300 0 C 16500 F - - — Pomatoceros triqueter 0 P R 0 2 0 — ** * -
F. vesic. f» linearis - - - R 5 C R 2 F - - - — — — — Bangia • - - - F 3 F Scytosiphon — R P F Table 3.1.1 CSU and OPRU Abundance Estimates for MG6 - MG9 57 Col 1 i OPRU Abundance Estimate (Max) Col 2 i CSU Estimate (Max); % cover for Plants and Mytiluo; No ./r/ for Col 3 * OPKU conversion of CSU animals
MG7B UG8 MG8A MG9 Species 1 2 3 1 2 3 1 2 3 1 2 3 Grimmia maritima - Ramalina 0 P R 0 P R 0 P R F 4 C Grey Green Lichens s 72 S S 72 S s 56 S S 50 S Orange Red Lichens A 40 A A 40 A A 24 A C .5 C Verrucaria maura Ex 95 Ex Ex 100 Ex Ex 94 Ex Ex 100 Ex . Verrucaria mucosa C 1 C F 11 C F 4 C F 10 C Lichina confinis ------0 P R 0 p E Hildenbrandia 0 P R 0 P R F P R 0 p K
Ulva lactuca 0 P R R P R - - — 0 p F Enteromorpha ------F 7 C Cladophora 0 P R F 15 C C 31 A C 29 C
- - - Pelvetia canaliculata ------
Fucus spiralis - — Fucus veBiculosus ------— Fucus serratus R P R ------Himanthalia elongata — - - Ascophyllum nodosum ------Laminaria digitata s 86 S S 91 Ex s 88 S A 24 c Laminaria saccharina - - - — ------Laminaria hyperborea ------Alaria esculenta 0 2 F 0 4 F F 3 F C 55 A Lithothamnia s 54 S Ex 68 S A 27 A Ex 95 Ex Porphyra umbilicalis 0 P R F 15 C C 15 C A 65 S Gigartina stellata F 4 F F 35 A F 3 F F 4 F - Chondrus crispus ------Catanella repens ------•• C e ramium/Cal 1 it hamn ion F 2 F 0 4 F F 3 F F 7 Polysiphonia lanosa -
Lomentaria articulata ------Dumontia incrassata ------Codium fragile ------
Palmaria palmata - - - 0 P R - - - - - Corallina officinalis F 4 F F 1 0 F 2 F F 7 Laurencia hybrida - — Laurencia pinnatifida R P R — — — — - — - Balanus balanoides A 8290 F S 6500 F A 8290 F A 7860 r Littorina "saxatalis" Ex 5790 F s 3438 F S 4830 F S 3016 F Littorina littorea ------
Littorina 1ittoralis ------Gibbula cineraria ------Patella S 212 Ex Ex 217 Ex s 96 A A 134 3 Nucella lapillus c 9 F - - - c 8 C - - - Mytilus F 3 F C 13 C C 31 A C 42 A — * Spirorbis - - - - • ------
Pomatoceros triqueter — — •* — — — — - • • *
Bangia 0 2 F 0 8 c R P R c 20 C Scytosiphon - - - 0 3 F 0 P R 0 4 F Porphyra linearis 0 P R — • — — — 0 P R Table 3.1.1 (cont) CSU and OPRU Abundance Estimates for MG6 - MG9 58
"CSU" method) are Riven in Table 3.1.2. below:
Site . OPRU "CSU1 MG6 4.25 4.50 MG6A 3.75 3.75 MG7 3.50 3.50 MG7A 2.75 2.75 MG7B 2.00 2.25 MG8 2.00 2.00 MG8A 1.75 1.75 MG9 1.25 1.00
Table 3.1.2 Exposure Grades from OPRU and "CSU" Methods
The abundance scores for the lichens and the algae appear to be
approximately the same using the two methods, although the abundance
score is often one category higher using the "CSU" method. However, when a species is rare, the "CSU" method can produce a much higher
assessment of % cover if the plant happens to fall within the quadrat and falls under several intersections. This was particularly the case with Fucus vesiculosus f. linearis on the transects being studied.
For the animals, there is often a difference of one category using the two methods, but the discrepancy may occasionally be considerably more for the smaller organisms. The abundance assessment was consistently- higher using the OPRU method for Balanus balanoides and Littorina
"saxatalis
While there may be considerable differences in the abundance assessments using the two methods, the exposure grades calculated from the two sets of data were the same or within 0.25 unit of each other. This demonstrates the strength of the exposure grading technique in that the separate abundances of thirty-one species are compounded to produce a single exposure grade value by an equal weighting technique.
It may appear, therefore, that more precision in the abundance measuring technique is not required. While the modification of the CSU method appears to be precise,
it may be worth noting several difficulties that arose in obtaining
accurate counts. On a shore where there is considerable overlapping
of seaweeds, it was difficult to maintain the location of plants below
the top layer while manoeuvring the latter. In this process, the
quadrat might also be moved, and so the question of whether the plant
was lying beneath a particular intersection became subjective. This
problem became more difficult on the lower shore when the occasional
wave shifted the position of lower shore algae such as Laminaria digitata. Another difficulty arose with convolutions of the rock
surface causing some parts of the quadrat to be some distance away
from the rock. This made sitings through the intersections of the quadrat open to some subjectivity. Finally, it was apparent that
there must be considerable error in the counting of small organisms
such as Spt-rorbis within small sample areas and attempting to multiply these figures out to give numbers per square metre.
If actual abundance measurements as produced by the "CSU" method were to be incorporated into the exposure scale, there would have to be a method of ensuring that each species had the same weight in the exposure grading process. Without such a weighting process, smaller organisms with their greater potential abundance would have more in- fluence in determining the exposure grade of a shore. The weighting process would have to make the abundance of each species into a ratio of the maximum abundance possible. This could be incorporated into pro- gram BALL 3. In the present form of the exposure scale, the abundance categories as used in the OPRU method provide a form of weighting process that appears to be adequate. The above investigation shows that the adoption of "CSU" methods to the OPRU weighting process does little to change the results of an exposure grade analysis. There 60
appears to be little point, therefore, in using the more lengthy
"CSU" method, particularly if its apparent precision may be suspect.
3.2 Data Collection - Selection of Different Vertical Intervals
The standard vertical sampling interval chosen for most shores
in Shetland was 0.2 m. With a spring tidal range of around 2 m.,
this would ensure at least 10 stations on a sheltered rocky shore
transect. As mentioned previously, increasing exposure causes the
littoral plant and animal zones to be raised well beyond the tidal
range, thus making the adoption of a 0.2 m. vertical range impractical.
In order to limit the number of stations on a transect to a reasonable number, the vertical interval for exposed shores was raised from
0.2 m to 0.5 m or 1.0 m. The rationale behind this selection is
illustrated in Table 3.2.1 below, where the heights of various transects
around Mavis Grind are compared.
Transect Exposure Height of Height of Height No . stations at No. Grade top sta. bottom difference 0.2 m. 0.5 m. 1.0m. sta m. m. m. vertical intervals
MG5 7.50 2.50 0.50 2.00 10 -
MG6 4.50 3.80 0.20 3.60 19 -
MG7 3.50 3.40 0.20 3.20 17 -
MG8 2.00 5.20 0.20 5.00 26 -
MG9 1.75 6.90 0.40 6.50 - 14 8
MG10 0.50 9.40 0.40 9.00 - 10
MG11 0.00 18.50 1.00 17.50 - 19
Table 3.2.1 Selection of Vertical Interval in Relation to Exposure of Stiore
It can be seen that up to MG8, a 0.2 m. vertical interval is manageable, although the 26 stations required here do involve much effort, with many stations having similar abundances of the same species as the transect passes through a zone. For MG10 and MG11, a 1.0 m. vertical interval is appropriate, whereas for MG9 a 0.5 m. or a 1.0 in. vertical interval could be selected. For a marginal site such as this, a different vertical interval may provide different abundance assessments.
At any particular station, the abundance of a species must be averaged over the whole area defined by +0.5 and -0.5 vertical interval above and below the station. If the species is present in a small, zone that does not fill a whole station at 1.0 m. vertical interval, its abundance will be less than if its zone were fully within a station provided by a smaller vertical interval. It is clear that the vertical interval selected must allow for at least one station within each of the major zones.
In order to test the effect of selecting a different vertical interval, MG9 was scored with stations at 0.5 m. and 1.0 m. vertical intervals. The abundance measurements are best compared by reference to Figure 3.2.1 where kite diagrams for selected species are shown.
In this case it can be seen that the selection of the larger vertical interval may cause the maximum abundance score of a species to be one category lower than if the smaller vertical interval were selected.
This difference in maximum abundance scores has made no difference to the exposure grade for the site derived from the two sets of data.
In both cases it is Grade 1.75.
It may be concluded that care should be taken in the selection of the vertical interval that is appropriate to the shore being studied.
However, in the one test case that is described here, the exposure grading technique was powerful enough to be unaffected by the few differences in maximum abundance score caused by the selection of a different vertical interval. rw. cko/t«Utum
3.f
5L.1
Verrucaria Alaria esculenta Porphyra Gigartina stellata Ceramium Ba lanus Patella My tj lus mucosa edul is umbTI ical is C|l lithimnion balanoides Loft side of axis is assessment at 1 m. vertical interval 2 mm. = one Right side of axis is assessment at 0.5 m. vertical interval abundance category Figure 3.2.1 Kite Diagrams for Selected Species at MG9 Assessed at cn Different Vertical Intervals K) 63
3.3 Preparation of Exposure Scale - Cycling of Computer Smoothing Proccss,
In the preparation of the exposure scale, the.standard set of
species abundances was produced in an averaging and smoothing process
carried out by programs BALL 2, BALL 2A, and BALL 3. The process
was carried out twice; firstly allocating the species maximum scores
for each site to a whole unit of exposure, and secondly allocating
them to the | unit exposure grades produced by the first run of the
programs. Reference to Figure 2.3.5 will remind the reader of this
cyclical procedure. The exposure scale that was selected consisted of the standard species abundances produced by the second cycle.
The final exposure grades were those produced by this scale on the
second round of the cycle. It was considered useful to look into
the effect of further cycles on the standard species abundances and the exposure grades produced from these.
Programs BALL 2, BALL 2A, and BALL 3 were incorporated as subroutines into a covering program called BALL. The output from each subroutine was printed, and the appropriate information was passed to the next subroutine. BALL was set for 10 cycles such that the printed output for each cycle consisted of the average maximum score for each species for each exposure grade, followed by these values smoothed by a polynomial expression (the standard species abundances) followed by the exposure grades from these standards.
The exposure grades for the ten cycles are given in Appendix 4.
It will be noticed that the fluctuation in exposure grade does not usually exceed one unit of exposure, although the fluctuations sometimes cause a departure from the expected exposure grade with an increasing number of cycles. Sites that were originally Grade 0 stay the same, while those sites that were originally Grade 1 or Grade 2 decrease gradually with increasing cycles towards Grade 0. This usually 64 begins after the third cycle. Sites of Grade 3 - Grade 5 are not affected by the cycling process while sites of Grade 6 and Grade 7 sometimes stay the same and sometimes increase to Grades 7.75 or
Grade 8.00. Sites that were originally Grade 8.00 or Grade 9.00 stay approximately the same throughout the cycling process. In order to be able to explain this general drift towards the extremes of exposure, the abundance curves of selected species for different cycles have been plotted in Figure 3.3.1.
It can be seen that there is no regular pattern in the way that the abundance curves change with increasing cycles. However, it is clear that each time the exposure grade of a site is changed by BALL 3, its attendant species abundance scores will go with it for the recalculation of mean abundance scores per exposure grade at the beginning of the next cycle (BALL 2). This will change the abundance curves most greatly for those species with a large range of abundances provided by the sites in each grade. The large range in abundances would be due to the species responding to another variable besides wave action. The least reliable species (as an indicator of wave exposure) at any particular exposure grade will show the greatest fluctuation in abundance curve. For example, from Figure 3.3.1, this means that Laminaria digitatci is not as reliable throughout the exposure range as Fucus vesiculosus.
The way that the exposure grades change for any particular site will depend on which species that site is mainly relying on for its assessment. If it depends mainly on unreliable species, then its exposure grade may be expected to fluctuate continuously with increasing cycles. In this study, it has been noticed that sites of Grade 3 -
Grade 5 stay approximately the -same throughout the cycling process. 65
Abundance Score
Fucus vesiculosus Laminaria digitata
Abundance Score
5 9 5 9 Exposure Exposure Grade Grade Alaria esculenta Balanus balanoides
lsttcycle 2nd cycle 10th cycle Figure 3.3.1 Effect of Cycling Computer Smoothing Process on Abundance Curves of Selected Species e>6
This may be because.sites in the middle of the exposure range have a rich flora and fauna and therefore it is likely that the abundance curves of many reliable species will be used in their location on the exposure scale. The grades of sites on the exposed or sheltered end of the range tend to move towards the extremes with an increasing number of cycles. This is perhaps due to the reduced flora and fauna on these shores giving a smaller number of species available for giving the shore a sensitive location on the exposure scale, particularly at the exposed end. The abundance curves of Alavia esculenta (Figure
3.3.1.) show a progressive swing towards the exposed end of the scale with an increasing number of cycles. It seems likely that if this swing is repeated for other species that are indicative of exposed conditions, then the grades of exposed shores will become progressively more exposed.
This in turn will affect the abundance curve in the same direction on the next cycle to produce the observed result that once a shore begins to move towards one of the extremes, it is carried on in that direction by the cyclical process.
It is clear that increasing the number of cycles in the averaging and smoothing process does not increase the accuracy of the exposure scale. This is because the species that are used in exposure grading are not perfectly reliable in terms of wave exposure. Often their abundance is influenced by something other than wave exposure to produce the undesirable variation in abundance at each grade of exposure.
It may be concluded that two cycles of the process are justifiably required in producing an exposure scale to a precision of £ unit of exposure. Beyond two cycles, it is possible that the extra precision that may be expected is lost because the data processing departs too much from the original data. This sort of limitation must be realised in a cyclical analysis of this kind. 3.4 Operation of Exposure Scale - the Effect of Using a Different
Species Selection.
The exposure grading process involves the use of program BALL 3
with which the species maximum scores of a test site are compared
to the standard set of species abundances. As previously mentioned,
only those species that appear to be reliable indicators of exposure
or shelter are used in this process. They were selected after con-
sidering their original abundance curves together with their seasonality
and occurrence on different shores (section 2.3). Thirty one species
were used in the normal exposure grading process and these are listed
in Table 3.4.1. For a variety of reasons, it was considered useful
to investigate the effect of changing the species selection on the
exposure grade that is assigned to a shore. Firstly, it was apparent
that oil pollution was influencing the exposure grade of MG2 : By
eliminating from the analysis those species that were judged to be
susceptible to oil pollution, it was thought that the "true" exposure
grade of the shore might emerge. Secondly, it was clear that there
would be a saving of time and effort if the number of species that
were recorded and used in the exposure grading process could be reduced.
The reduced species sets that were employed are listed in Table
3.4.1 and consist of the normal species set minus pollution sensitive
species; plants only; animals only; fucoids only; and "strong species".
"Strong species" were defined as those from the normal species set
that have a good modal abundance curve and that are fairly common
throughout the year. The various species reductions were applied to
all the biological data that had been obtained to date which included
the 83 Shetland sites that have already been described, together with data from different times of year from Mavis Grind sites. The exposure
grades that were produced for each site using the various species
selections are given as Appendix 5. 68
1. Normal Species Set 2. Normal Species Set Minus Pollution Sensitive Species 3. Plants Only 4. Animals Only 5. Fucoids Only 6. "Strong Species"
1 2 3 4 5 6
Verrucaria mucosa XXX Lichina confinis XXX Hildenbrandia Ulva lactuca Enteromorpha Cladophora Pelvetia canaliculata X X X X Fucus spiralis X X X X Fucus vesiculosus X X X X Fucus serratus X X X X Himanthalia elongata X X X X Ascophyllum nodosum X X X X Laminaria digitata X X X X Laminaria saccharina X X X X Laminaria hyperborea Alaria esculenta X Lithothamnia X Porphyra umbilicalis X X Gigartina stellata X Chondrus crispus X X Catanella repens Ceramiuiq/Callithamnion X Polysiphonia lanosa X Lomentaria articulata Dumontia incrassata Codium fragile Palmaria palmata X X. X Corallina officinalis X X Laurencia pinnatifida X X X Laurencia hybrida Balanus balanoides Littorina "saxatalis" Littorina littorea X Littorina littoralis X Gibbula cineraria X X Patella X X Nucella lapillus Mytilus edulis X X Spirorbis X X Pomatoceros triqueter X F-i vesic. f. linearis X X Gelidium pusillum X X Ectocarpus X X Porphyra linearis X X
I Table 3.4,1 Species Selections for Exposure Grade Production . 69 •
The seasonal work will be described and discussed in greater
detail in section 5.1. At this stage, it is sufficient to note that
the exposure grade produced from the .normal species set for MG2 became
progressively higher (more sheltered) during 1978. Over this same
period, a small amount of oil was noticed continuously trickling into
the sea near to the site. An examination of the raw biological data
revealed that the abundances of a number of species at this site had
drastically changed during the recording period, presumably due to
the oil pollution. Reference to Appendix 5 will show that the omission
of these pollution sensitive species from the species set did little
to stabilise the change in exposure grade. In a similar way, the exposure grade was highly variable when the plants only or the animals only were considered. However, when the "strong species" set was applied
to the seasonal data for MG2, a constant exposure grade of Grade 6.00 was produced each time the site was recorded after February 1978. In this case it is clear that those species that collectively respond most strongly to the exposure gradient were least affected by the oil pollution.
When other less responsive species are removed from the species set, these "strong species" (Table 3.4.1) produce what may be considered as the "true" exposure grade of the shore.
In comparing the exposure grades from the species reductions with those from the normal species set, it is the "strong species" that produce the most similar exposure grades. The case of MG2 demonstrates that the "strong species" set may produce an even better estimate of the exposure grade. This is certainly the case for 0P55 which is a shore with a highly particulate substrate. The full species set gives this shore a grade of Grade 9.00, whereas the exposure grade produced by the "strong species" set is Grade 4.50. The latter grade is more realistic considering the available fetch. The coefficients of similarity to each grade of exposure for OP55 have been plotted
in Figure 3.4.1. Using all the species in the exposure grade
determination, it .can be seen that the curve is rather flat, indicating
an even similarity to many grades. The maximum similarity is at
Grade 9.00, but a small secondary peak may be seen at around Grade 4.50.
Using the "strong species" only, similarity is increased for all
grades of exposure but the secondary peak is increased further to provide the maximum similarity at the middle of the exposure range.
In general, the species reductions do not produce grades greatly different from those produced by the normal species set, and usually they are within one unit of exposure. However, when fucoids only are considered, there may be larger discrepancies, particularly at the sheltered end of the range. Surprisingly, the exposure grades at the exposed end of the range, where fucoids are less abundant, more faithfully resemble those produced by the normal species set. It appears that exposed shores with an original exposure grade of less than Grade 4.00 can tolerate a reduction in the species set of both the plants and the animals, ftowever, sheltered shores require both plants and animals for the production of a realistic exposure grade.
If the animals only are considered, the exposure grades are too low
(exposed) and if the plants only are considered, the exposure grades are too high (sheltered). This is obviously reflecting the general observation that animals are more in evidence on exposed shores whereas plants dominate the sheltered shore scene. For reliable exposure grading, a selection of plants and animals must be scored.
A reduction of the full species set to a consideration of the "strong species" only may produce the most accurate exposure grades. At this stage, it must be pointed out that without physical measurements, there is no way of accurately assessing the "correct" exposure grade Coefficient of Similarity
Exposure Grade
Figure 3,4.1 Coefficient of Similarity vs. Exposure Grade for 0P55 using May 78 Data. of the shore. The assessment of the most "realistic" exposure grade is rather subjective, but based on a selection of alternatives provided by the different species sets.
One final observation arising from this work is that the time . of year most suited to a reduction of species from the normal set is early summer. The smallest differences between exposure grades produced by different species sets are at this time of year when the biota is probably at its healthiest and most representative after the spring growing period. However, it should be noted that the only reduction in species that is recommended is one that includes only the best plant and animal indicators of wave exposure.
3.5 Summary
The preparation and use of the Shetland exposure scale closely followed a pattern very similar to that used for the Norwegian exposure scale. It has been demonstrated, that the methods used were adequate and that the selection of different methods does little to change the apparently accurate exposure grades produced by the original technique. The effect of this has been firstly to show that the exposure grading process can be streamlined and made much quicker.
Only the abundances of a limited species set provided by the 19
"strong species" need be recorded. For each species at any site, it is sufficient to record only its maximum abundance using the relatively quick "OPRU method". Secondly it has been shown that the technique has a certain amount of tolerance in that in a marginal case, the selection of a different vertical interval for abundance measurements did not influence the outcome of the exposure grading technique. Later on, it was demonstrated that in the preparation of the scale the use of only two smoothing cycles was justified. 73
CHAPTER 4
The Effect of Environmental Variables Other than Wave Action on Exposure
Grade
The biological exposure scale uses the littoral flora and fauna to
indicate the wave exposure status of a particular site. An inherent ass- umption is that the ecology of rocky shores is related primarily to wave action and that the influence of other environmental variables is negligable
in comparison. The effect of other environmental variables on the rocky
shore community is well documented (Lewis, 1964), but these effects are
generally insufficient to produce drastic changes which will influence tlie exposure grading technique. However, when a physical factor other than wave action becomes extreme, it may have an over-riding influence on the ecology of the shore. For example, when a rocky shore becomes very steep,
the algal zones tend to be replaced by a dense covering of barnacles. Bio-
logical data from such a shore applied to the exposure scale would not produce a grade representative of the general wave exposure status of the
site. In an attempt to define the limitations of the exposure scale, physical
data was collected from each of the original 83 Shetland sites.
4.1 The Environmental Variables
An attempt was made to categorise and measure all the most important physical factors that may influence the distribution and abundance of
organisms on rocky shore. These were considered to be:
Exposure Factors Secondary Physical Factors Fetch 90° to shore Aspect Maximum fetch Angle of slope of shore Distance to outer coast Rock type Minimum width of channel to Surface texture outer coast Angle subtended by sea horizon Degree of fissuring Angle of transect in relation to Roughness of shore middle of max. fetch % transect stones/silt Depth offshore Density of stones Salinity Since direct physical measurements of wave action were impractical
for the size of this study and indeed unavailable at this stage, various
indirect measures of the amount of wave action were made. Fetch measurements relating to the distance over which waves may be generated were obviously likely to be important. For each site, the fetch perpendicular to the shore and the maximum fetch available to the
shore were measured from maps. On the outer coast, these figures would be very large, but their effect is likely to be modified by the configuration of the coast, and whether the site is located on a headland or in a bay. As an indicator of this, the angle subtended by the sea horizon at each site was measured with a compass. On the inner coast, there would be no sea horizon, but there may still be some influence of the swell from the outer coast. The penetration of the swell to the inner coast would depend on the distance of the site from the outer coast and the minimum width of the inlet from the outer coast. These two parameters were measured from maps. A further consideration relating to the fetch was the angle of the transect in relation to the maximum fetch, or if appropriate, the middle of the sea horizon. It was thought that if the dominant waves were likely to come from this direction, then a transect facing it would be more exposed than one at an angle to it. The appropriate angle was calculated for each site by finding the difference between the direction of maximum fetch from a map and the aspect of the transect as measured at the site.
Another environmental variable likely to influence the amount of wave action arriving at a site is the depth offshore. Deep water will mean that larger waves will be able to break against the shore whereas shallow water might cause the waves to break offshore or at least cause dissipation of some of their energy. Two measures of depth offshore were obtained from Admiralty Charts. One was the distance to the 5 fathom contour and the other was the maximum depth within 1 mile perpendicular to the shore.
The environmental variables described above may be considered " as "exposure factors" because their relative values describe the conditions for the formation and modification of waves before they hit a shoreline site. In this context, they may be considered to be the primary physical factors in determining the ecology of the shore and its associated exposure grade. Various secondary physical factors may also be recognised which may influence the ecology of the shore primarily determined by its exposure to wave action. These factors are considered below.
The aspect of the shoreline was considered by Lewis (1964) to be important in that a north-facing shore would receive less sunshine and therefore would generally be damper than a south-facing shore. He suggests that this would favour the development of some species, while other species such as Lick-ina confines would prefer a sunny south-facing shore.
Many of the other physical factors that have an influence on the ecology of the shore may be related to the geological composition of the underlying rock. Southward (1953) states that varying geological composition itself will not greatly influence the zonation on the shore, but Lewis (1964) comments that the very soft rocks such as chalks, shales, limestones and some sandstones may be less suitable for barnacles, limpets and fucoids. Myxophyceae and Enteromorpha spp will generally become dominant on these rocks.
The lithology and structure of the rock is undoubtedly of importance 76
when considering the surface texture of the rock masses. Igneous
and metamorphic rocks usually become weathered so that their surfaces
are pitted and rough, with many fine cracks. These conditions will
favour organisms such as littorinids and Helvetia - the former finding
adequate shelter, while sporelings of the latter attach and survive
well in the rougher texture of the rock. Smoother surfaces are more
suited to species such as Venmcaria and Porphyra. In addition,
flat areas of smooth sedimentary rocks will favour Porp/zj/ra/Myxophyceae
and Mytilus/Rhodophyceae communities. Thus the zonation of the species
on the shore may be substantially modified by the surface texture
and degree of fissuring of the rock.
The overall slope of the shore is an important modifying factor
controlled by the geological characteristics of the rock. The overall
slope of the shore may control the effectiveness of wave action -
steep shore tending to concentrate the maximum impact of the waves
over a small area. In addition, a steep slope will necessarily have
thinner bands of species in the zonation, which may lead to the
exclusion of some of the bands due to the lowered chance of successful
breeding (Rees, 1935). Furthermore, steep slopes will tend to drain
more rapidly than shallower slopes, again tending to reduce the extent
of the zonation. It appears that the overall effect of a steep slope
will be to increase the mechanical action of the waves, but to reduce
their wetting action. A limit may be reached with a vertical surface
when wave action may be reduced due to the forming of standing waves
or a claposis. Evans (1947 b) states that a steep slope will also make the settlement of algal spores more difficult, but apparently
encourages the development of barnacles and littorinids. This is
presumably the result of the beneficial effects of rapid water movement
for feeding. 77
The topography and overall roughness of the shore are also important:
influences on its ecology (Kitching, 1934). Granite tends to form
smooth slopes and rounded boulders, while sandstones produce ledges
and rectangular shapes. Slates'and shales produce jagged ridges if
the angle of bedding is suitable. A rough shore with steeply dipping
strata and large boulders will aid wave energy dissipation, and have more rock pools, and generally have a longer drying time on emersion.
The effect of a rough shore on its ecology is thus to reduce the mechanical effect of wave action, but to increase the wetting effect.
The zonation will tend to be less distinct than on a smoother shore.
The stability of the substrate is another variable connected with the underlying geology of the shore. Boalch (1957) noticed no change in abundance with substrate in Beer Bay, Devon, but this may have been because the smallest boulders were large enough to be immobile.
When the boulders become small enough to be rolled by wave action, there is a drastic reduction in the number of species - particularly of the seaweeds.
In order to study the effect of these secondary physical factors, it was necessary to quantify them. The aspect of the shore was easily measured as being the compass bearing of the axis of -the transect.
The overall angle of slope of the shore from top to bottom station on the transect was measured at each site using a clinometer. If there was a large change in slope down the shore, then the individual slopes were measured and the one corresponding to the mid shore region was selected for use in any analysis.
At each shoreline site, the rock type was noted and checked against One-Inch Geological Maps, or where not available, a Quarter
-Inch Geological Map. The sites were distributed among six major rock types as follows:
Schist & Gneiss 33 Limestone 7 Granite 19 Old Red Sandstone 7 Diorite 14 Tuffs and Lavas 3
As already mentioned, it was clear that the rock type would influence
a variety of characteristics such as the surface texture and degree
of fissuring of the rock which would require more detailed assessment.
In the absence of any documented method for quantifying these variables,
both were assessed against arbitrary scales.
The scale for the surface texture assessment was as follows:
1) Flat, smooth surface of fine-grained rock 2) Smooth surface of rock, may have minor undulations 3) Small scale rough surface, indentations no larger than a few millimetres.. Blocky rock surface. 4) Roughness measurable as "centimetre cubes" of rock, indentations reasonably shallow. Typical of granite in Shetland. 5) Very rough, contorted rock surface.
The scale for the degree of fissuring assessment was as follows: 2 1) Less than 0.1 m / 0.1 m 2) 0.1 - 0.5 m / 0.1 m2 3) 0.5 - 1.0 m / 0.1 m2 4) 1.0 - 1.5 m / 0.1 m2 5) More than 1.5 m / 0.1 m 2
It is appreciated that both these scales involve a large amount of subjectivity. The surface texture scale is open to a variety of interpretations and similarly the degree of fissuring scale will depend on the individuals own assessment, of what constitutes a fissure in this context. However, since in this study only one person was involved with the assessment over a limited period, it was thought that these scales might produce a useful guide for the comparison of shores.
In order to ensure that the interpretation of the scales did not change over the recording period, the following procedure was adopted: Firstly,
a representative portion of the shore was selected for the placing 2 ... of the 0.1 m quadrat. The surface texture and degree of fissuring
grades were then assessed in the field, and a black and white photograph
was taken of the quadrat* After all the sites had been recorded, the
photographs were ranked in the laboratory, firstly in order of surface
texture, and secondly in order of degree of fissuring. In each case
the photographs were divided into five groups corresponding to the
grades on the scale. In this way, a laboratory assessment of each
variable was obtained for each site. Where the laboratory assessment
differed from the field assessment, the site was considered from
memory and the photograph, and one of the two estimates was chosen.
This constituted the final assessment for the site.
The overall roughness of the shore was measured in the form of
a ratio. A tape measure was carefully laid down the length of the
shore such that it closely followed the rock surface down any gullies
and over any ridges. This length was then divided by the length of
the tape when stretched^tight to produce the Roughness Ratio. At
each site this was done along the axis of the transect and repeated
at a distance of 1.5 m. to the left and 1.5 m to the right of the
axis in order to provide a mean Roughness Ratio for the whole transect.
A histogram showing the distribution of the sites along a range of
Roughness Ratios is given in Figure 4.1.1.
Various measurements were made in an attempt to quantify the presence of any loose material on the transect. Stones with any 2 dimension larger than 5 cm. could be estimated in terms of numbers /m .
Counts were taken in a representative area at the top, middle and bottom of the shore. Stones smaller than 5 cm. were usually too numerous to could and were estimated as % cover over the transect area as a Frequency 10
1.01 i*33 Roughness Ratios
Figure 4.1.1 Roughness Ratio Frequency Histogram R.A.D. WIUUHT, BOTANY DEPT., . .IMPERIAL COLLEGE DATS : 51 wert
SITE NAME/No VOU"' ^^ 0S WAP KEF: HU * PHOTO No: 2ft, JL<\ > So
Fotch 903 to shore (km) ; . R'lS, Anp.lo subtended by sea horizon:,
. Los. Maximum foteh (kia) • •••• ... • Anp.le of transoct in relation Dt^ld/VCi- ic U31I ^ t wMt*^ to middle of Feteh in prevailing (jcr\) ^ So fn Aspect :J?5 Angle of slope of shore . \Z Rock Type s Schist- % Surface Texture (Depressions counted are those over 1 cm in width and depth along six parallel equally spaced in 0.1 m2 quadrat (each parallel approx 30 cm long)) 1. Very smooth flat surface 2. Globular surface, similar to coarse-grained granite, few depressions greater than 1 cm width or depth 3. Rough surface, but less than 50 depressions/180 cm length 4. Rough surface, 50 - 150 depressions/ 180 cm length 5. Very rough surface, with more than 150 depressions/180 cm Degree of Fissuring Ftet* ftNrtt 1. Less than 0.1 m / 0.1 m2 2. 0.1 - 0.5 m / 0.1 m2 3. 0.5 - 1.0 m / 0.1 m 4.- 1.0 - 1.5 m / 0.1 m2 5. More than 1.5 / 0.1 m2 Roughness of Shore Mean Roughness Ratio Roughness 1. Length of tape over rocks (m) Length of tape stretched tight (in) ^r.o 1.1^ 2. Length of tape over rocks (m) ** l» H Length of tape stretched tight(m) s,^ 3. Length of tape over rocks (m) ^^ Length of tape stretched tight(m) l Mobility of Substrate transect stones up to 5 cm :...... transect silt : Approx density of stones larger than 5 cm Top Shore s •. .1.« Middle Shore / Low Shore s.. 7\ / m Depth Offshore Distance to 5 fathom contour (km) : Maximum depth 1 mile perpendicular to shore»...... fathoms Salinity (Zo) 31. t Figure 4.1.2 Example of a Physical Data Sheet whole. Similarly, a figure for the % transect covered by silt was also obtained. It was thought that for most sheltered shores, silt and stones smaller than 5 cm. in any dimension would be the most important in determining the mobility of the substrate. One final environmental variable that needed to be measured was salinity. Most intertidal organisms cannot tolerate reductions in salinity over long periods. The effect of this on Fucus serratus and Ascophyltum nodosum in sheltered area has already been commented upon in section 2.2. At each site the conductivity of the water was measured using a conductivity meter, and after noting the temperature of the water, its salinity could be found by reference to conversion tables (Home, 1969). In order to simplify the recording of all these environmental variables, a physical data sheet was produced, an example of which is given as Figure 4.1.2. The information on the complete set of physical data sheets for MG1-MG11, SH12-SH43, and 0P44-0P83 is given on Fiche 3. 4.2 The Environmental Variables Related to Exposure Grade For each site, a set of physical variables had been measured and an exposure grade had been determined from biological data. It has already been mentioned that the physical factors may be divided into two groups. There are the "exposure factors" which will have a primary influence on the biota and consequently the exposure grade that is assigned to a shore. The other group may be considered as the secondary physical factors which will possibly modify the biota and cause errors in the exposure gradings which should be due to the "exposure factors" alone. A close relationship is therefore desired between the exposure grade and the various "exposure factors" while 83 it is hoped that the secondary physical factors are independent of exposure grade. In order to have a better understanding of these relationships, program GRAPH was written to produce sqattergrams with exposure grade on abscissa and the various physical factors as ordinates. The listing of GRAPH may be found on Fiche 1 in a modified form as a subroutine of Program ENV. The physical variables that were measured as "exposure factors" are: • Fetch at 90° to the shore Maximum fetch Modified maximum fetch Angle subtended by the sea horizon Maximum depth offshore Distance to 5 fathom contour It was soon apparent that the fetch variables were closely related to the exposure grade in an exponential manner. Program GRAPH was therefore modified so that the logarithm of the physical factor could be plotted against exposure grade. Figure 4.2.1, on arithmetic scales, shows depth offshore related to exposure grade. A measurement of the distance to the 5 fathom contour does not appear to be worthwhile since the distance for sites at most grades of exposure is small, except for a small number of sites at the sheltered extreme. The measurement of the maximum depth offshore shows a smoother trend from large depth at exposed sites to shallow water at sheltered sites. Figure 4.2.2 shows the natural logarithm of the angle subtended by the sea horizon plotted against exposure grade. This shows a fairly good straight line relationship for those sites that have a sea horizon, although the number of these sites is limited. Figures 4.2.2 and 4.2.3 show the natural logarithm of various measures of fetch plotted against 2.320 I 0 a.:>m i 1 2. T2 7 [ 5 2.101 I T 2.134 I ft 2.C3U I M 2.043 I C 1.933 r £ 1.3-VJ I 1.102 f t i. tm r 0 1.813 I 1.763 I 5 1.717 I 1.G70 I F 1.624 I ft 1.070 I T 1.531 I H 1. 405 I 0 1.430 I M 1.302 I 1.346 I C 1.299 X N0 1.201.2536 I I T 1.160 I 0 1.114 I U 1.057 I R 1.021 I .974 I .923 I .002 I .835 I .789 I .742 I .698 I .650 I .603 I .557 I .510 I .464 I .410 I .371 I .27.3258 I r .232 I .185 I .139 I .093 I .0460 I — 4 5 EXPOSURE GRADES 54.000 I 52.920 I * 51.040 I 50.760 I 49.680 I 46.600 I 47.520 I 46.440 X 45.350 I * 44.280 I x 43.200 I * 42.120 I * 41.040 X 39.960 I * 38.880 I 37.800 r * * 36.720 I 35.540 1 34.560 I 33.480 I * * 32.400 I 31.320 I 30.240 I 29.160 I * x * x 28.080 I 27.000 I 25.920 r * 24.840 I XXX 22.682J.760 I I * 21.600 I XX X 20.520 I 19.440 I x 18.36C I X X 17.200 I 16.200 I 15.120 I 14.040 I 12. Figure 4.2.1 Depth Offshore Variables vs. Exposure Grade ,n* r, 1 l 4, 1 4 I 0 4 I f 4, J 4.',M 1 i 4, . 441 I t 4 .3-1" 1 n 4, .vm I 4. 1-V, I H 4, .040 I 0 3. .044 I R 3, .043 1 I 3, ,742 1 Z 3, .640 I 0 3, ,530 I N 3, ,430 I 3, ,337 I 3, .236 I 3. .135 I 3, ,034 I 2, ,033 I 2, ,Q31 I 2, ,730 I 2, ,629 I 2, ,528 I 2, ,427 I 2. .326 I 2, ,225 I 2. .124 I 2. ,022 I 1. ,021 I 1, ,020 I 1. ,710 I 1. ,618 I J. ,517 I 1. ,416 I 1. ,315 I 1. ,213 I 1. ,112 I 1. ,011 I ,010 I ,609 I ,708 I ,607 I 506 I ,404 I ,303 I 202 I 101 I 0 X X X X X X X X X X X X X X X X X- 4 5 6 7 0 9 EXPOSURE GRflOES 8.556 I 9 8.293 I 0 8.030 I 7.767 I F 7.503 I x x E 7.240 I T 6.977 I C 6.714 I H 6.451 I 6.187 X 5.924 I 5.661 I 5.398 I 5.134 I 4.871 I 4.608 I 4.345 I 4.061 I 3.818 I 3.555 I 3.292 I 3.029 I 2.765 X 2.502 I 2.239 I 1.076 I 1.712 I X X 1.449 X 1.186 I X X .023 I XXX .659 I .396 I .133 I -.130 J -.393 I -.657 I -.020 I -1.183 I -1.446 I -1.710 I -1.073 I -2.236 I -2.499 I -2.763 I -3.026 X -3.289 I -3.552 I -3.815 I -4.079 I -4.342 I -4.605 EXPOSURE GRADES Figure 4.2.2 Angle of Sea Horizon and 90° Fetch vs. Exposure Grade n n.* * 1f. n nii.jj. l.iv I X 7.7.11( ''" !I i 7.4//.;>v.1i I Ii. 7. milI rH. li.Uti.Ul'.P) I r>ii. :iti*iriI7> •i.7•i.tlM3) JI r,.oi5.200o I 5.004.0642 I 4.434.6470 I 3.094.2103 I 3.778 I 3.563.3414 I 2.913.1270 I 2.472.6953 1I 2.042.2561 I 1.601.8274 I 1.389 I X X 1.172 I X X .73.9505 I X X .30.5214 I -.13.0661 I -.56-.3405 IX -1.00-.7820 I -1.43-1.2147 I -1.86-1.6501 I -2.30-2.0835 I 4 5 EXPOSURE: GRADES 8.420 I M 8.113 I * * 0 7.807 I D 7.500 I * 1 7.194 I * F 6.887 I * I 6.560 I E 6.27-1 I D 5.967 X * 5.661 I * M 5.354 I fl 5.046 I X 4.741 I 4.435 I XX F 4.128 I XX E 3.821 I T 3.515 I * C 3.208 I * H 2.902 I 2.595 I 2.289 I 1.982 I 1.676 X 1.369 I 1.063 I .756 I .449 I X .143 I * -.164 I xxx -.470 I xxx -.777 I X xxx xx -1.083 I * xxx xx -1.390 I * * xx xxx -1.696 I xx -2.003 I xx -2.310 I -2.616 I * -2.923 I xx -3.229 I x x v -3.536 I * -3.842 I * -4.149 I X -4.455 X X -4.762 I * -5.068 I * -5.375 I X * * -5.602 X X -5.988 I -6.295 X X -6.90-€.6081 I —————— — * 0123 456 7 8 EXPOSURE GRADES Figure 4.2*3 Maximum Fetch and Modified Maximum Fetch (Logarithms) vs. Exposure Grade S6 87 exposure grade. Although a trend is visible, there is a fairly wide scatter of points for the 90° fetch and the maximum fetch. For the latter, many sites at the exposed extreme have the same maximum fetch and clearly some modification of this parameter is desired. A modified maximum fetch was described in section 2.3 which incorporates coefficients relating to the angle of sea horizon and the maximum depth offshore. As can be seen from the scattergrams, these were indeed the most useful "exposure factors" to select. The modified maximum fetch is shown plotted against exposure grade in Figure 4.2.3, and it is clear that this modification of the maximum fetch provides the closest relation- ship with exposure grade. It was considered useful to pursue the idea of finding a close relationship between a modification of fetch and exposure grade since this might allow the exposure grade of a shore to be predicted from a number of physical attributes that could be measured from a map. The following modifications of the maximum fetch were calculated using program ENV (see Fiche 1): Mod Fetch 1 = MF X (SH/180)*X MW/(DIST + MW) Mod Fetch 2 = MF X (SH/180)*X D/60 Mod Fetch 3 = MF X (SH/180)*X MW/(DIST + MW) X D/60 * only included if SH exists. In order to overcome this, SH was modified for the fetches above as follows: Mod Fetch 4 = MF X (SH + 180)/180 X MW/(DIST + MW) Mod Fetch 5 = MF X (SH + 180)/180 X D/60 Mod Fetch 6 = MF X (SH + 180)/180 X MW/(DIST + MW) X D/60 where MF = Maximum Fetch (km) SH = Angle subtended by sea horizon MW = Minimum width of channel to outer coast (km) DIST = Distance to outer coast (km) D = Maximum depth offshore (fathoms) It can be seen that originally SH was expressed as a ratio of the maximum likely to be observed and only included if a sea horizon existed. This was clumsy and involved actually reducing the value of a maximum fetch if a sea horizon existed. Later modifications of 88 • the maximum fetch were considered more suitable where the addition of 180 to SH before division by 180 made this ratio always greater than unity if a sea horizon existed and merely unity if one did not. The coefficient relating to the penetration of swell from the outer coast would be unity at the outer coast since DIST would be zero and MW could be any value which would be divided by itself. A site on the inner coast would have its maximum fetch reduced by this coefficient since as the distance from the outer coast increases, the coefficient becomes smaller. The depth offshore may always be considered as having a reducing effect on wave action below a certain threshold value. In the absence of a threshold value, the maximum depth within 1 mile of the shore was selected as the denominator of the coefficient. From the scattergrams relating exposure grade to exposure factor, it was clear that maximum fetch, angle of sea horizon and maximum depth offshore were important parameters. It was certain that these should be used in producing a modified fetch value such as Mod Fetch 5. The effect of including the distance from outer coast coefficient (Mod Fetch 6) was investigated by plotting Mod Fetch 5 and Mod Fetch 6 against exposure grade and fitting a regression through the points (Figure 4.2.4). In both cases, the natural logarithm of the modified fetch value were used. The statistics may be summarised as follows: X = Natural log of Modified Maximum Fetch 5 Y = Exposure Grade Y = 5.1684 - 0.4365X Correlation coefficient between X and Y = -0.781 X = Natural log of Modified Maximum Fetch 6 Y = Exposure Grade Y = 4.1287 - 0.3832X Correlation coefficient between X and Y = -0.834 It is clear from Figure 4.2.4 that there is little visual difference between the plots produced by the two modifications of fetch. Since MOD FETCH 5 VS E.G. • a a o -8.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00 NAT LOG MOD FETCH 5 MOD FETCH 6 VS E-G • a naa an ana n D- ra -!i.~o .no '.•on i.iiu i.on .1.00 N«t L no ;i('!) -HTf.M G Figure 4.2.4 Modified Fetch 5 and Modified Fetch 6 vs. Exposure Gra.de ST 90 the inclusion of the distance from the outer coast coefficient increases the correlation, it was decided that this modification of fetch (Mod Fetch 6) would be most useful in predicting exposure grade from physical attributes. The distribution of the secondary physical factors in relation to exposure grade is shown on the scattergrams in Figures 4.2.5 - 4.2.8. Figures 4.2.5 and 4.2.6 show that there is little relationship between exposure grade and the angle of the transect in relation to the dominant wave direction, aspect, texture, or degree of fissuring. Figure 4.2.7 shows that perhaps there is a trend for exposed shores to have a steep slope and a high Roughness Ratio, although these trends are not well defined. The particularity of substrate measurements are represented by the percentage of the transect covered by small stones as plotted against exposure grade in Figure 4.2.8. This scattergram shows that particulate substrates are limited to the sheltered end of the exposure range. It does not show that exposure grade is influenced by particularity but merely shows that particulate substrates and high exposure grades (sheltered) are produced at the same sites. Reference to Figure 4.2.8 shows that salinity remains uniformly high across the exposure range, although it may occasionally be reduced at the sheltered end. The distribution of all the environmental variables in relation to exposure grade is further illustrated by examination of correlation coefficients. The correlation coefficients between all the variables were calculated by a simple program called STATS. It is listed on Fiche 1 as a subroutine of program ENV. The correlation coefficients between the environmental variables and exposure grade are illustrated schematically in Figure 4.2.9. It can be seen that the variables most highly correlated positively with exposure grade are the particularity 123.000 I L lio.oo120.04o0 rI 0r m.io110.62o0 II 110.700 I T 100.240 I ft 105. 700 I Nft 100.06103.320 I t 5 00.400 I C 90.940 I C 93.400 r T 91.020 I t 0(1.0606.100 I M ai.in03.640o I i R 70. 720 I E 70.260 I L 73.BOO I n 71.340 I T GO.000 I 1 65.420 I 0 63.960 I N 61.000 I 59.040 I T 56.000 I 0 54.120 X 51.660 I M 49.200 I 1 46.740 I 0 44.200 I 0 41.020 X L 39.360 X E 36.900 I 34.440 I 0 31.900 X r 29.520 X 27.060 X 5 24.600 I 22.140 X xxx H 19.600 I 17.220 X 14.760 X 12.300 I 9.040 I 7.300 X 4.920 X 2.460 X :: ; i 345 EXPOSURE GRADES 351.000 I * 343.980 I * * * 336.960 I * 329.940 X * 322.920 X * 315.900 I x * * 308.080 I 301.060 I * 294.840 I * x xxx 287.020 I . * 260.600 I at 273.780 X * xxx 266.760 I * * 259.740 I * * 252.720 I * 245.700 I xxx x 238.600 I * 231.660 I 224.640 I 217.620 I * * 210.600 ix*. x 203.580 I * x 196.560 X * 189.540 I * 102.520 I * 175.500 I xx 160.480 I 161.460 X * 154.440 X 147.420 X xx 140.400 I x.x 133.380 I * x 126.360 I X x x x 119.340 I .* 112.320 X x x 105.300 I .xxx 98.280 I 91.260- X 84.240 I * xx 77.220 I 70.200 X xx 63.180 X xx .56.160 X x 49.140 X * 42. 120 I xx 35.100 I x 21.C628.000 I I 14.040 X * * 7.020 X 0 * * * x 0 1 2 3 4 5 6 7 'a 3 EXPOSURE GRADES Figure 4,2.5 Angle of Transect in Relation to Max Fetch and Aspect vs. Exposure Grade X XXX * * * * -X * X * X X X X XX X XX X EXPOSURE GRADES 5 .000 r D 4 .900 X E 4 .800 I G 4 .700 I R 4 .600 I E 4 .500 I E 4 .400 I 4 .300 I 0 4 .200 I F 4 .100 X 4 .000 I xxx xx F 3 .900 I I 3 .800 I S 3 .700 I S 3, .600 I u 3. .500 I R 3, .400 I I 3. .300 I N 3. .200 I G 3, . 100 I 3. .000 I XXX XXX XXXXXXX XX XXX X X 2, ,900 I 2. .800 I 2. ,700 I 2. ,600 I 2. .500 I 2. ,400 I 2. .300 I 2. ,200 I 2. .100 I 2. ,000 I XX X xxxxx 1. ,900 I 1. .800 I 1. ,700 I 1. 600 I 1. 500 I 1. 400 I 1. 300 I 1.20 0 I 1.10 0 I 1.00 0 I X X 900 I 800 I 700 I 600 I 500 I 400 I 300 X 200 I 100 I EXPOSURE GRADES Figure 4.2,6 Texture and Degree of Fissuring vs. Exposure Grade EXPOSURE GRADES 1.330 I 1.271.3073 X 1.221.2540 XI 1.171.1907 X 1.111.1447 XI 1.091.0614 I 1.011.0317 IX .95.9884 I .93.9014 I .87.0581 XI .79.8285 I .74.7715 X .71.6982 I .63.6685 I .58.6125 XI .53.5592 XI .47.5095 I .42.4562 XI .37.3992 XI .31.3469 IX .26.2963 I .21.2393 X .106 X .13.1630 IX .106 I .000 I .02.0573 I EXPOSURE GRADES Figure 4,2.7 Angle of Slope and Roughness Ratio ys. Exposure Grade 00.COO I cp o'l.roOft.40o0 ir E 04.r,00 I N 03.000 I r 7i.?ooi.ooo ri r3 77.40>5.0000 r i 73.000 I 5 72.000 I r 70.200 I n ro.coen.40o0 ri E 64.000 r 5 63.000 I 61.200 r 59. 400 I 07.600 I SI.000 I 54.COO I 52.200 r 50.400 I 46.000 I 45.0046.000 I r 43.-700 r 41.400 I 39.600 I 37.800 I 36.000 I 34.200 I 32.400 r 20.0030.6OO0 X I 27.000 r 25.200 t 23.400 I 21.600 I . 10.0019.000 I I 16.200 X 14.400 I 12.600 I 10.800 I 9.000 I • 7.200 I 5.400 I 3.600 I 1.000 X EXPOSURE GRADES 35.500 I 34.790 I 34.080 I 33.370 I 32.660 I 31.950 I 31.240 I 30.530 I 29.820 I 29.110 X 28.400 I 27.690 I 26.980 X 26.270 I 25.560 I 24.850 I 24.140 I 23.430 I 22.720 I 22.010 I 21.300 r 20.590 X 19.880 r 19.170 I 18.460 I 17.750 I 17.040 I 16.330 I 15.620 I 14.910 X 14.200 I 13.490 I 12.780 i 12.070 I 11.360 I 10.650 r 9.940 I 9.230 I" 8.520 I 7.817.100 I r 6.390 I 5.680 X 4.970 I 4.260 I 3.550 I 2.132.840 I r 1.420 X .710 I EXPOSURE GRADES Figure 4,2.8 Percentage of Stones on Transect and Salinity V3• Exposure Grade PERFECT -f- CORRELATION 1.0 3 % silt 0.5 % stone < Distance to 5 fathoms <] No. stones mid; No. stones bot. <1 No. stones top — ' — — — o.l/d <1 L of transect in rel to S.H. — — — — 1 Si _ 1$ <1 Aspect <3 Degree of Fissuring < Salinity W < Texture — — — - - - - < L of slope — — - • -0.1% < 90 Fetch; Mod Max Fetch; Roughness Ratio -0.5 O L of Sea Horizon < Max Fetch < Max Depth Offshore 1.0 PERFECT - CORRELATION Figure 4.2.9 Correlation Coefficients between Environmental Variables and Exposure Grade 96 factors whereas the "exposure factors" are the best to be negatively correlated. This is as to be expected since high values for the exposure factors coincide with low exposure grades (exposed shores) whereas high values for the particularity factors coincide with high exposure grades (sheltered shores). While this analysis provides useful information as to the distribution of the environmental variables in relation to exposure grade, it does not indicate the importance of any physical factor in influencing exposure grade. 4.3 The Relative Importance of the Environmental Variables On the assumption that most of the physical characteristics of the shores had been accounted for in the measurement of the environmental variables, various ordination techniques were applied to the data in order to identify those variables that were responsible for most of the variation. Ordinations produced by a Principal Components Analysis (Orloci, 1966) and Correspondance Analysis (Reciprocal Averaging; Hill, 1973) appeared to be the most appropriate. In both cases, computer programs written by A.J. Morton of Imperial College were available on library files. In the Principal Components Analysis, it was necessary to standardise the data to zero mean and unit variance such that each attribute would have the same weighting. This would ensure that the principal components were not selected on the basis of high numerical values alone. Without this standardisation, attributes such as the various measures of fetch would be given exceptionally high weightings in the analysis due mainly to their potentially high numerical values. The standardisation was carried out within the program. In the first analysis, the exposure grade for each site was included with the values for the 18 environmental variables. The outcome was that 97 exposure grade was given a high value on the first Eigen Vector, with little separation of the other variables. From this it was clear that much of the variation in the data could be related to the exposure grade of the shore. Since the relative importance of the physical attributes was required, it was decided to omit exposure grade from the second Principal Components Analysis. The Principal Components Analysis technique can be imagined as producing a cloud of points for the 83 sites in hyperspace, with one axis for each attribute measured. The successive Principal Components are mathematically independent axes through the cloud of points in hyperspace, each accounting for progressively smaller amounts of the total variance. Associated with each Principal Component is an Eigen Vector giving a measure of the correlation between each attribute and the component in question. The values for the first vector are shown diagrammatically in Figure 4.3.1. It can be seen that with the exposure grade excluded, the most important components are the exposure factors (less than -0.2) and the particularity factors (greater than 0.2). This is further demonstrated by considering the coordinates for each of the 82 sites in the cloud obtained by trans- forming the Eigen Vector (Orloci, 1966). When the values for Vector 1 are plotted against those for Vector 2 as in Figure 4.3.2, the greatest separation is given to two groups - the exposed shores and the particulate shores. In this analysis, 27.2% variation was accounted for by the first Principal Component and 16.8% by the second, making a total of 44.0% for the two Principal Components. It was thought that a Correspondance Analysis ordination may provide further information since it gives simultaneous ordinations of sites and attributes which may be superimposed. The axes for the site ordination are directly compatable with those for the attribute 98 0.4 < % stones 0.3 < No. stones mid % silt; No. stones top <1 No. stones bot. 0.2 <1 Distance to 5 fathoms < L of transect in rel to S.H, 0.1 ^ Aspect -0.1 Salinity Degree of Fissuring L of slope Texture -0.2 < 90 Fetch ^ Max Fetch; Mod Fetch ^ L of Sea Horizon -0.3 Roughness Ratio Max Depth Offshore -0.4 Figure 4.3.1 Distribution of the Environmental Variables on the First Eigen Vector of the Principle Components Analysis. Vector 1 gg Particulate Shores -2 Vector 2 * • • • •• • • • • Exposed Shores -6 Figure 4.3.2 Vector 1 vs. Vector 2 for Sites in Principle ^ Components Analysis 100 ordination. It is also often very successful in displaying the main gradient of variation in a body of data. The scatter of points within the first two axes for the ordinations are shown in Figure 4.3.3. It can be seen that the sites are grouped neatly into areas corresponding to the exposure factors and the particularity factors. Very few sites are located in an area occupied by most of the other environmental variables. Having isolated the most important environmental variables that describe the physical characteristics of a shore, a multiple regression analysis was used to relate them more precisely to exposure grade. Program REGRESS, copied from Davies (1971) was used for this purpose. The various exposure factors were considered as the independent variables (X) that could be related to the dependent variable of exposure grade (Y) in the form: Y = b.x. + b~x0 + ... + b x + c 11 3 3 mm The natural logarithms of the independent variables were used since these were individually related to exposure grade in a linear form. As listed in Table 4.3.1, various multiple regressions were carried out with different exposure factors. In each case, the pro- 2 portion of the total variance in exposure grade (R ) that could be accounted for by the exposure factors was computed. An F value 2 was also computed such that the significance of R could be tested by using the number of independent variables and the number of sites to indicate degrees of freedom. In all cases, the F ratio was highly significant since for typical degrees of freedom of v^ = 4 and v^ — 78, the F ratio for significance at P = 0.001 was only 5.20. As can be seen from Table 4.3.1, 70% variation is accounted for by using all the exposure factors. Omission of the 90 fetch does not change R , but Axis 1 101 100 r • • *v 50 • • Exposed Shores 50 100 Axis 2 Site Coordinates Axis 1 100 . * % silt stones • Dist to 5 fathoms . Others 50 L of S.H. f Max fetch Mod Fetch 90 Fetch —» i— t « i 1 50 100 Axis 2 Environmental Variable Coordinates Figure 4.3.3 Plots of Reciprocal Averaging Ordinations 102 Regressions in formi Y = bjXi • b2X2 • b3X3+ b4X4+ C Angle 90° Max of Sea Max Dist to Exp. Fetch Fetch Horizon Depth S fathoms Grade R2 F x X X X X 0.70 36 i 2 3 4 5 Y X X X 0.70 45 1 *2 3 4 Y X X X Y 0.68 57 1 2 3 X X Y 0.64 47 1 H 3 Natural logarithms of X and arithmetic values of Y were used Table 4.3.1 Multiple Regressions between Exposure Factors and Exposure Grade . 103 it does increase its significance due to the smaller number of. variables used. Further omission of either of the depth offshore variables 2 reduces R slightly, but increases its significance. The significance (indicated by F) is greatest when the maximum depth offshore value is used in conjunction with maximum fetch and angle of sea horizon. The multiple regression is: Y = -0.221X^ - 8.661X2 - 0.925X3 7.778 where Y = exposure grade X^= nat log maximum fetch X2= nat log angle of sea horizon X^=. nat log maximum depth offshore 2 Since 68% variation in exposure grade (R ) is accounted for in this regression, it was considered to be a useful expression with which to predict exposure grade from physical variables. Various secondary physical- factors were added to the multiple regression in order to see what additional proportion of the total variance they account for. Addition of the angle of slope of the 2 shore increased R to 70% but its significance decreased. When various 2 . particularity factors were added, R increased to 81% although its significance decreased further. It can be concluded that the two most important groups of environmental variables influencing exposure grade are the exposure factors and the particularity factors. From these analyses, the other environmental variables appear to be of little importance. In further analyses, it was decided to separate the exposure factors from the secondary physical factors and consider the effects of the latter in greater detail. 4.4 The Effect of Secondary Physical Factors on Exposure Grade It has been demonstrated above that exposure grade can be calculated 104 from the exposure factors by using an expression derived from a multiple regression analysisi The most appropriate expression was shown to be as follows: Y = 0.221XX - 8.661X2 - 0.925X3 7.778 where Y = exposure grade X^ = nat log max fetch X2 = nat log angle of sea horizon X^ = nat log max depth within 1 mile offshore Using this relationship, the "expected" exposure grade could be cal- culated for each site from its exposure factors. The "expected" and the "observed" exposure grades were obviously highly correlated (r = 0.823) as was shown when the two estimates were plotted (Figure 4.4.1). It is interesting to note that at the exposed end of the range, some sites were expected to have a negative exposure grade when calculated from the exposure factors. Perhaps these sites were indeed more exposed than the biological exposure scale could indicate? On the other hand, at the sheltered end of the range, no sites were expected to have an exposure grade of Grade 9.00 on the basis of the exposure factors. Perhaps the exposure grade of Grade 9.00 was produced by some physical factor secondary to wave exposure? If it is tentatively assumed that the expected exposure grade calculated from exposure factors gives a "true" estimate of the exposure status of a shore, then any deviations in the observed exposure grade might be due to the influence of secondary physical factors on the species composition of the shore. In order to investigate this, the "Observed - Expected Exposure Grades" were calculated for the 83 sites and plotted against each of the secondary physical factors. A linear regression was put through the scatter of points. Program ENV 2 was written for this purpose. The first part of the program calculates the expected exposure grade and the Observed - Expected exposure grade for each site. Y= 1 . 4404 + . 68005X Figure 4.4,1 Observed vs. Expected Exposure Grade 106 Subroutine LINREG calculates a linear regression of the latter with each of the secondary physical factors. Subroutine GRAPH 2 plots the scattergram and subroutine RPLOT adds the regression line. ENV 2 is listed on Fiche 1. The various plots may be found in Figures 4.4.2 - 4.4.7. For many of the environmental variables, there is an even scatter of points above and below the Obs-Exp Exposure Grade = 0 line. In these cases the regression line appears to follow the axis and have a gradient approximating to zero. Environmental variables in this category include the angle of the transect in relation to the dominant wave direction, the aspect of the shore, the surface texture of the rock and the salinity of the surrounding waters. It may be deduced- that these environmental variables do not cause a trend in the deviation of the observed from the expected exposure grade. However, there are other environmental variables where such a trend may be recognised and described by the gradient of the regression line. In these cases, a value of d was calculated for each regression in order to check that the gradient of the line differed significantly from zero, (d = X / (s/V^ri) ; Bailey, 1959). Environmental variables having a regression line significantly different from zero were the angle of slope of the shore, degree of fissuring, the Roughness Ratio, and the various particularity factors. It may be concluded that these environmental variables may cause the observed exposure grade to differ appreciably from the expected exposure grade. If a deviation of one exposure grade from expected is assumed to be unacceptable, then it is possible to calculate limits from the regression equations for the usefulness of the biological exposure scale in relation to each of the physical variables. The limits are found by substituting +1 and -1 for Y in the linear regression equations. M5-EW E .C.QAOE Y => -.10053 + .00240 X 5.0 I 4.0 I 4.a I 4.4 I 4.2 I 4.0 r 3.8 i X 3.6 i 3.4 r 3.2 i 3.0 i 2.8 i 2.a X X 2.4 i 2.2 i X 2.0 i X l.O X X 1.6 I X 1.4 I X 1.2 I X 1.0 I .a I * .6 I * .4 I * .2 I X X * -.0 X X X X x_x~x -.4 * -.6o ;I -1.0 X x x -1.2 I X X -1.4 * X XX -1.6 * -i.a * -2.0 I -2.2 I -2.4 I -2.6 I -2.3 I -3.0 I -3.2 I -3.4 I -3.6 X -1.-3.80 II -4.2 I -4.4 I -4.6 I -4.8 X -5.0 I- 20.50 41.00 61.50 62.00 102.50 123.00 L OF TRANSECT IH RELATION TO MID OF SEA HORIZON • MAX FETCH oes-exp Y = -.03606 + .00019 X E.GRADE 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 .4 .2 -.0 -.2 -.4 -.6 -.8 -1.0 -1.2 -1.4 -1.6 -1.8 -2.0 -2.2 -2.4 -2.6 -2.8 -3.0 -3.2 -3.4 -3.6 -4.0 -4.2 -4.4 -4.6 —4.8 -5.0 58.50 117.00 175.50 351.00 ASPECT Figure 4.4.2 Observed - Expected Exposure" Grade vs. Angle of Transect in Relation to Max Fetch and Aspect 107 C.GRADE Y " 1.20016 • -.07100 X 5.0 I 4.H I 4.6 I 4.4 I 4.2 I 4.0 I 3.0 I * 3.5 I 3.4 f 2.64 I * * 2.2 I * 2.l.0o rI * * x 1.64 rI * * * * 1.20 I. * * .or..* * .«4 1* • • * • * _;20 *i *—*—* * x-x-x—. x_.* -.-'.24 1X * * * -.6 I -1.-.00 II -1.24 II -1.60 Ir -2.0 I -2.24 II -2.6 I -3.-2.0 II . -3.42 I -3.60 II - -4.-^.02 I -4.—4.64 I I -3.0-4.8 II 17.67 25.50 ANGLE OF SLOPE OBS-EXP E. GRADE Y = 5.67248 + -4.99539 X 5.0 I 4.8 I 4.6 I 4.4 I 4.2 1 4.0 I 3.0 r X 3.6 I 3.4 I 3.2 I 3.0 I 2.8 I * 2.6 I * 2.42 I* * * 2.0 I * 1.8 I xx 1.6 x * 1.4 X * * xx 1.02 I * xx .8 1 xx .6 . xxx .41.*.*. xx x .2 X x ... x x x . -.• I X X X . . X . X X X -.2 1 * • -.4 1 * * * * ... — 61 xxx ~'.e i * -1.0 I xxx -1.2 I * * .4 i * * * -1.6 I * -1.8 I xx -2.0 I * -2.2 I x -2.4 X * -2.6 X • xx -2.8 X -3.0 I * -3.2 X -3.4 I x -3.6 X -3.8 I . -4.0 I -4.2 X -4.4 X —4.6 X -4.8 I —5.0 X 1.01 1.06 1.12 1.17 ROUGHNESS RATIO Figure 4.4,3 Observed - Expected Exposure Grade vs. Angle of Slope and Roughness Ratio I o% cos-ew E.csnoe r = .61533 + -.10072 X 5.0 I 4.0 I 4.6 I 4.4 I 4.2 I 4.0 I 3.8 I X 3.6 I 3.4 I 3.2 X 3.0 I 2.0 I X 2.6 X 2.4 I X 2.2 X X 2.0 I X 1.8 I X X l.B I X 1.4 I X X X 1.2 I X 1.0 X .8 I X X .6 I X X X .4 X X X .2 X X —.0 T -.2 I X -.4 I X X X -.6 I X X X -.8 I X X -1.0 I X X -1.2 I X X -1.4 X X X -1.6 I X -1.8 r X X -2.0 i X -2.2 X -2.4 I X -2.6 I X X -2.8 r. -3.0 i X -3.2 i -3.4 i X -3.6 i -3.8 i -4.0 i -4.2 i -4.4 X -4.6 i —4.8 r —5 0 j 1 .00 1.67 2.33 3.00 3.67 OBS-EXP E.GRADE T = .98610 + -.36056 X 5.0 I 4.8 I 4.6 I 4.4 I 4.2 I 4.0 I 3.8 * 3.6 I 3.4 I 3.2 I 3.0 I 2.8 * 2.6 * 2.4 * 2.2 * * 2.0 * 1.8 I * 1.6 I * 1.42 *I ' * * 1.0 * .8 1 * .6 . * * .4 * x -.0 .2 I -.4 I -.6 r -.8 I -1.0 I -1.2 * -1.4 I -1.6 I -1.8 I -2.0 I -2.2 * -2.4 X -2.6 I -2.8 I -3.0 I -3.2 I -3.4 I -3.6 I -3.8 I -4.0 X —4.2 I —4.4 I -4.6 I -4.8 I -5.0 I- 3.00 DEGREE OF FISSURING Figure 4.4.4 Observed - Expected Exposure Grade vs Texture and Degree of Fissuring 2103 005-CW c.nnnoe Y = -.26093 +• .03601 X 5.0 4.0 4.G 4.4 4.2 4.0 3.0 3.6 3.4 3.2 3.0 2.0 2.6 2.4 2.2 2.1.03 1.0 1.4 1.2 1.0 .8 .6 .4 .2 -.0 -.2 -.4 -.5 -.8 -1.0 -1.2 -1.4 -1.6 -1.8 -2.0 -2.2 -2.4 -2.6 -2.8 -3.0 -3.2 -3.4 -3.6 -3.8 -4.0 -4.2 -4.4 —4.6 -4.8 -5.0 30.00 45.00 PERCENTAGE OF STONES OBS-CXP E. GRADE Y = -.22869 + .08147 X 5.0 4.8 4.6 4.4 4.2 4.0 3.0 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 .8 .6 .4 .2 -.0 -.2 -.4 -.6 -.8 -1.0 -1.2 -1.4 -1.6 -1.8 -2.0 -2.2 -2.4 -2.6 -2.8 -3.0 -3.2 -3.4 -3.6 -3.8 ^.0 10.00 15.00 20.00 PERCENTAGE OF SILT/SANO Figure 4,4.5 Observed - Expected Exposure Grade vs. Percentage of Stones and Silt on the Transect 110 cns-op Y 19315 • .047C9 X E.GRACE 0.0 I 4.0 I 4.6 [ 4.4 r 4.2 i 4.0 i 3.0 i 3.0 i 3.4 i 3.2 i 3.0 i 2.0 i 2.6 r 2.4 X 2.2 I 2.0 I 1.0 X 1.6 X 1.4 X 1.2 X 1.0 I .0 X .6 X .4 X .2 X -.0 XX -.2 -.4 X -.6 X. -.0 X -1.0 X -1.2 I* -1.4 XX -1.6 X -1.8 X -2.0 X -2.2 X -2.4 X -2.6 X -2.8 I -3.0 X -3.2 I -3.4 X -3.6 I -3.8 r -4.0 I -4.2 I -4.4 I —4.6 I —4.8 I -5.0 I— 40.00 53.33 NO STONES / M2 TOP OF TRANSECT CSS-EXP E.GRACE Y = -.21688 + .04286 X 5.0 I 4i8 I 4.6 I 4.4 I 4.2 I 4.0 I 3.8 I 3.6 I 3.4 I 3.2 I 3.0 I 2.8 I 2.6 I 2.4 I 2.2 I 2.0 I 1.6 X 1.6 I * 1.4 X 1.2 X l.O I .8 X .6 X X .4 X .2 X X -.0 X -.2 X -.4 -.6 X X -.8 X -1.0 X -1.2 XX -1.4 XX -1.6 IX -1.8 X -2.0 X -2.2 X -2.4 x -2.6 X -2.8 I -3.0 X -3.2 I -3.4 X -3.6 I -3.8 I —1.0 I -4.2 I -4.4 I -4.6 I —4.8 I -5.0 I— 33.00 49.50 66.00 93.00 NO STONES • M2 MIDDLE OF TRANSECT Figure 4.4,6 Observed - Expected Exposure Grade vs. No, stones top and middle of Transect Ml 005-CW v - - 23316 + .04310 X E.CRAOr».Co r T . OBS-EXP E.GRADE Y = 5.71014 + -.16930 X 5.0 I 4.8 I 4.6 I 4.4 I 4.2 I 4.0 I 3.8 I 3.6 I 3.4 I 3.2 I 3.0 I 2.8 I 2.6 I 2.4 X 2.2 I 2.0 I 1.8 I 1.6 I 1.4 I 1.2 I 1.0 I .8 .6 i .4 i .2 i -.0 i- -.2 X -.4 i X XX -.6 i -.8 i -1.0 i -1.2 i -1.4 i -1.6 i -1.8 i -2.0 i -2.2 X -2.4 I -2.6 I -2.8 I -3.0 I -3.2 I -3.4 I -3.6 I -3.0 I -4.0 I -4.2 I —4.4 X -4.6 I -4.8 I -5.0 I- 31.03 32.15 35.50 SALINITY Figure 4.4.7 Observed - Expected Exposure Grade vs. No. stones on bottom of transect and Salinity Ml 113 The values of X in each case will be the values of the physical variable when the observed exposure grade is ± 1 unit of exposure different from that expected from the exposure factors. The regressions and the limits relating to each of the physical variables are detailed in Table A.A.I. It is clear that the angle of slope of the shore is an important variable in relation to exposure grade. A steep shore will concentrate the force of the waves and appear to be more exposed than expected from the exposure factors. Slopes steeper than 32° will make a site appear to be more than 1 unit of exposure more exposed than expected. A shallow slope will dissipate much of the force of the waves up the shore, and will thus appear to be more sheltered. Shores with a slope of less than A° will appear to be more than 1 unit more sheltered than expected. •The degree of fissuring scale ranges from 1-5, and thus all the grades of this scale will fall within ± 1 unit of the observed - expected exposure grade. Similarly, the limits for the Roughness Ratio fall outside the measured limits for Shetland. A shore that has a Roughness Ratio greater than 1.33 will be one unit more exposed than expected. This result is unusual in that one would expect a high Roughness Ratio to cause dissipation of the waves' energy and a shore to be more sheltered than expected. However, a Roughness Ratio greater than 1.33 was not encountered in Shetland. Possibly the greatest deviations in the biological estimates of exposure grade are caused by the particularity factors. Percentage of stones, percentage of silt, and nos. stones / m all have an upper limit where the actual exposure grade becomes 1 unit more sheltered than.expected. As these factors increase, the mobility of the substrate 114 Regressions in formi Y = a> bX Significance of b tested by d wheret d = X / (e/VrT) Secondary Limits where Physical Y = + 1 Y -1 Factor a b d Signif. X X Aspect -0.036 0.0002 <1.5 Insig - - Angle of slope 1.280 -0.0719 4.831 0.1$£ 40 32° Texture 0.615 -0.1987 <1.5 Insig - - Roughness Ratio 5.675 -4.9954 3.025 1.$ 1 1.33 Fissuring 0.986 -0.3606 2.766 l.<# 0 5 % of Stones -0.270 0.0369 4.426 0.l£ C O 0 % of Silt -0.229 0.0815 3.859 0.l£ 15/£ 0 Stones/m^ top -0.199 0.0471 3.776 0.l£ 25 0 2 Stones/m mid -0.217 0.0429 4.047 0.1% 28 0 2 Stones/m bot -0.233 0.0431 3.527 0.\% 28 0 Salinity 5.710 -0.1693 <1.5 Insig - - Table 4.4.1 Observed - Expected Exposure Grade (Y) vs. Secondary Physical Factor (X) Regressions, with Limits on the Latter Variables increases, causing a reduction in the flora ai*d fauna on the shore, and subsequently pushing the biological exposure grade towards the sheltered extreme. This condition occurred at many sites in' Shetland and is typified by OP55 (Fugla Ayre, Sul.lom Voe) which has an observed exposure grade of Grade 9.00 although most stable sites in Sullom Voe have an exposure grade of Grade A/5. The anomaly can be explained by the highly particulate substrate consisting of 80% stones and 10% silt. The "one unit limits" for these variables are 3A% and 15% respectively. The most important environmental variables that may influence exposure grade appear to be the angle of slope of the shore and the particularity of its substrate. For the various environmental variables involved, the "limits" may be taken as representing guidelines outside which the exposure grading technique may be treated with suspicion. A.5 The Abundance of Fuous vesiculosis Related to the Particularity of the Substrate. The various secondary physical factors influence the exposure grade of the shore by providing conditions that will modify the distribution and abundance of species related to wave exposure. During fieldwork in Shetland it was noticed that the abundance of Fuous vesicuZosus appeared to be increased relative to AsooiphyZlum nodosum on sheltered shores with a highly particulate substrate. It was decided to investigate the relationship between the abundance of F. vesicuZosus and the particularity of the substrate. Program VESIC (see Fiche 1) was written to extract the maximum and mean abundance scores for F, vesicuZosus from the transect data. % stones, % silt, and nos. 2 stones / m data were extracted by hand from the physical data sheets and displayed along with the abundance data in Table A.5.1. Various statistics were computed by the MINITAB statistical package that was 116 Max, Mean No. Score Score Pcent Pcent StO! F. vesic F. vesic. Stones Silt Mid 1 1.00 5 0 0 4 3.00 20 1 10 5 2.50 15 5 20 7 4.86 35 10 7 5 3.83 10 0 2 6 3.43 0 0 1 4 2.80 5 10 0 6 4.57 90 30 15 4 2.25 5 30 15 4 3.00 5 2 0 4 2.78 10 10 0 2 1.50 8 5 2 4 3.25 5 5 2 6 3.33 5 0 5 6 5.20 5 10 50 4 4.00 5 0 8 6 3.75 40 20 30 4 3.29 80 10 26 4 2.80 65 30 8 3 2.33 10 0 1 2 1.50 2 0 0 5 3.22 15 0 99 5 3.17 5 20 15 6 5.60 15 0 2 4 3.25 2 0 5 4 3.00 15 0 6 5 3.11 80 5 50 Table 4.5.1 Abundance of Fucus vesiculosus and Particularity Data 117 available as library file. Correlation coefficients between the variables are shown in Table 4.5.2 below: A B C D B .972 i"c " " .384 ."343 1 i 1 i D .328 .264 1 .673 1 l E .352 .295 ! .499 .377 where A is the max score of F. vesi-culosus B is the mean score of F. vesiouZosus C is the % stones on the transect D is the % silt on the transect 2 E is the no. stones / m in the midshore region of the transect. Table 4.5.2 Correlation Coefficients between F. vesiouZosus Abundance and Particularity Factors The primary area of interest is enclosed by a dotted line. It can be seen that there is a higher correlation between the maximum score of F. vesiouZosus and the particularity factors than between the mean score and the particularity factors. The correlation coefficients for the maximum score relationships are all significant at the p = 0.001 level, and the most significant correlation is shown to be between the % stones on the transect and the maximum score of F. VesiouZosus. This relationship is shown plotted in Figure 4.5.1. It can be seen that the maximum score for F. vesiouZosus increases with % stones on the transect up to about 40%. This does not demonstrate that the abundance of F. vesicuZosus is dependent on the % stones, but it does show that the two variables are related. Beyond 40% stones, the abundance of F. vesicuZosus stays the same or perhaps even decreases. However, the overall abundances of species decline with increasing particularity due to the mobility of the substrate. While this does not prove the original hypothesis, it does not disprove it since the 118 Maximum Abundance Score for Fucus vesiculosus 7 2 • • •5 • • I i I^i i i » n I « 20 40 60 80 100 Percentage of Stones Figure 4.5.1 Maximum Abundance Score for Fucus vesiculosus vs. Percentage of Stones on the Transect relative proportions of F. ve.siculosus and Ascophyllum nodosum may change through competition (as found in Norway; Dalby et al (1978), although the abundances of both species are decreased when most of the transect is covered by small stones. It is clear that more work is necessary on this subject before precise conslusions can be drawn. 120 CHAPTER 9 The Effect of Time on Exposure Grade If the exposure grade of a shore is to represent accurately its wave exposure status, then for as long as there is no change in the overall wave climate, its exposure grade should remain constant with time. It is well known that the abundances of many littoral species show seasonal changes in relation to various climatic factors (Boney, 1966). It is also well known that abundances of species continuously fluctuate from year to year due more subtly to environmental factors in relation to chance biological events influencing reproduction and com- petition (Lewis, 1976). For the purposes of this study, it was con- sidered important to see how these natural changes in population density would affect the exposure grade that is assigned to a shore. A very detailed study of the ecology of rocky shores in north west Wales has been carried out by Jones et al (1980) since 1974. The abundances of species have been recorded from some sites at monthly intervals over this period, and seasonal and longer term trends have been recognised. The abundances of Ascophyllum nodosum> and the fucoids have shown little change throughout the recording period, although a steady decline in Fucus vesiculosus has been noted. These species, together with most animal species, rarely show regular seasonal changes in abundance. Their cycles of change appear to operate over longer periods extending to several years. This has already been documented by Southward and Crisp (1956) in a study of the relative proportions of Balanus balanozdes and Chthamalus stellatus on various rocky shores around the British Isles. Jones et al (1980) record that the biggest seasonal changes in abundance occur with plant species such as Porphyra umbilicalis3 Enteromorpha3 Viva lactuca3 and the Ectocarpaceae which have spring 121 blooms. A less dramatic summer increase is shown by species such as Gigavtina stellataj Lomentar-La art-iculata> and Palmar-ia palmata> while "lithothamnia" shows a summer decline. OPRU has been carrying out rocky shore surveys in Shetland since 1976. They record the abundance of species in May of each year as part of a biological monitoring programme. Their reports and their data have been used in an appraisal of the year to year variation in the abundance of species on rocky shores in Shetland. The raw data and the exposure grades calculated from it are commented upon later. In order to study the seasonal change in species abundances and exposure grade, it was necessary to establish sites for more frequent abundance measurements. 5.1 The Seasonal Study at Mavis Grind The area around Mavis Grind, North Mainland, Shetland was chosen for the study of the effect of seasonal changes in abundance on exposure grade. When the area was initially investigated in November 1977, it was decided that there should be some check on the seawater quality around two installations that might cause local pollution, and con- sequently complicate any conclusions drawn from supposedly natural species abundances. At Mavis Grind, there is a quarry and an asphalt plant from which a small stream flows into Sullom Voe. Oily water was discovered in this stream and was clearly visible as an oil sheen on a small part of the voe. At another location, sewage from the village of Brae is discharged into the voe. It was decided to assess the water quality of the voes to the east and west of Mavis Grind in relation to the proposed transect sites (see Figure 5.1.1). Water Sample Sites Proposed Transect Sites Scalei 2 cm.» 1 km. BRAE ROAD A970 Figure 5.1.1 Location of Proposed Transect Sites and Water Sample Sites at Mavis Grind 123 Water samples were first taken in February 1978. At each sampling site, two glass stoppered bottles were completely filled with water so that the samples had no contact with air. The bottles were chilled and transported to Imperial College for analysis. One bottle from each site was immediately stored at 20°C for the determination of the Biochemical Oxygen Demand (B.O.D.) while analyses proceeded using the other bottle. pH and conductivity were measured with appropriate instruments, and the salinity of each sample was obtained from the conductivity using a conversion table (Home, 1969). The oxygen concentration was determined using an oxygen electrode connected to a potentiometric recorder. B.O.D. was calculated by finding the drop in oxygen concentration after storage for 5 days at 20°C. Total nitrogen and total phosphorus concentrations were measured using colorimetric techniques in an autoanalyser after the samples had been acid digested (Allen et al, 1974). The results of these analyses are given in Table 5.1.1. The February 1978 phosphorus results were inexplicable in terms of causal factors and it was assumed that some of these samples had been contaminated. More samples were therefore taken in October 1979 at more locations (see Figure 5.1.1). Plastic bottles were used for sample collection at high and low tide. Each sample was filtered shortly after collection and then frozen for transportation to Imperial College. Analysis was again carried out on the autoanalyser, although this time the samples were not digested in acid. Reference to Table 5.1.1 will show that these results were more explicable in terms of causal factors. The salinities of all the samples were normal for sea water except for the sample that was taken near MG5 where there is some fresh water input causing dilution. All the samples were fully saturated with oxygen, while those for MG3, MG4, and MG5 were supersaturated, presumably 124 > > 7 P H 0 S PH ORU S H E 0 U mg/ 1 . I UJ 2 / 1 » ^ o o SATURATIO N / 1 is 'oo X m g 1 1 OXYGE N X H- o. NITROGE N _I y- B.0. 0 m g SAMPL E O O SALINIT Y °/ 0 A 0.0326 34.2 7.95 105 1.72 0.50 0.04 B 0.0326 34.2 8.06 105 0.11 0.50 0.05 C 0.0274 26.8 8.29 128 0.92 0.25 0.05 D 0.0325 34.1 8.22 122 0.34 0.50 0.07 0.04 £ 0.0328 34.4 8.19 116 1.15 0.75 0.05 F 0.0331 34.7 8.03 100 0.00 0.75 0.06 G 0.0325 34.1 7.99 99 2.53 1.00 0.04 0.07 . H 0.05 I 0.0328 34.4 8.03 100 0.00 0.75 0.06 0.06 J 0.0330 34.6 8.03 99 0.12 1.25 0.07 0.06 - K 0.0330 34.6 8.02 100 0.00 0.75 0.06 0.06 L 0.04 M 0.04 N 0.07 0 0.06 Phosphorus concentrations from samples collected in Oct 79 Other analyses from samples collected in Feb 78 Table 5.1.1 Water Quality around Mavis Grind 125 due to the fact that they were collected from amongst dense growths of Asoophyllum nodosum which would be photosynthesising. The sample taken at MG2 has a high B.O.D., possibly because of bacterial action on the oil trickling into the voe near to this site. The nitrogen concentrations from Feb 78 and the phosphorus concentrations from Oct 79 were generally close to the typical values of 0.5 mg/1 and 0.07 mg/1 respectively as cited in Home (1969). However, an increase in the nitrogen and a slight increase in the phosphorus concentration was detected around the sewage outfall from Brae, although the effect of this was not widespread. B.O.D. and nitrogen concentrations are shown symbolically in Figure 5.1.2. It has been demonstrated that the sewage outfall would not have a chemical effect on any of the transect sites proposed for the seasonal study. The thin sheen of oil that was visible around MG2 in November 77 and February 78 was present on subsequent visits through to 1980. It is clear that conclusions drawn from seasonal work at this site would have to be viewed with caution. Abundance measurements were recorded from transect sites MG1 to MG11 on the following occasions : Feb 78, May 78, Aug 78, Nov 78, June 79, Sept 79, Mar 80. The maximum abundance scores for each species for each occasion were extracted by program MAVIS and are displayed in Appendix 2. Exposure grades were computed by program BALL 3 and are given in Table 5.1.2. It can be seen that throughout the seasons, the exposure grade for any site appears to be extremely stable and does not change by more than 0.75 unit. The one exception to this is the grade for MG2 which progressively increases from Grade 5.25 in Feb 78 to Grade 7.75 in Nov 78 and then decreases throughout 1979 and into 1980. It was NITROGEN CONCS. mg/l B.O.D. CONCS. mg/l o 0.25 A 0 - 0.5 • 0.50 • 0.5 - 1.0 Figure 5,1.2 Nitrogen and B.O.D, Concentrations around • 0.75 • 1.0 - 1.5 Mavis Grind - Feb 78 • 1.00 1.5 - 2.0 1,25 2,0 - 2,5 M • to Feb 78 May 78 Aug 78 Nov 78 Jun 79 Sep 79 Mar 80 MG1 5.00 4.75 4.75 4.25 5.00 4.50 4.25 MG2 5.25 5.75 6.00 7.75 7.50 7.00 6.00 MG3 8.00 7.50 7.50 7.75 7.50 7.75 8.00 MG4 7.75 7.50 8.00 8.00 7.25 8.00 7.75 MG5 7.75 7.50 8.00 8.00 7.50 8.00 8.00 MG6 4.00 4.50 4.25 4.00 4.25 4.50 4.00 MG7 3.50 3.50 3.25 3.25 3.50 3.25 3.25 MG8 2.00 2.00 2.00 2.00 2.00 2.00 2.00 MG9 1.75 1.75 1.50 1.50 1.25 1.25 1.50 MG10 0.50 0.50 0.50 0.25 0.25 0.50 0.50 mu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Table 5.1,2 Exposure Grades in Different Seasons at Mavis Grind 128 at this site that oil was detected on the surface of the water on every occasion and it was deduced that the flora and fauna here is indeed influenced by oil pollution. The precise effects of the oil on species abundance and exposure grade will be described later. For the other sites, the exposure grades appear to be most stable at the exposed end of the range. The exposure grades for MG8 and -MG11 stayed at Grade 2.00 and Grade O.OO respectively throughout the recording period. In assessing change in exposure grade, the 1978 data were mainly considered since this was the time of year in which the sites were most frequently recorded. The records for June 79, Sept 79, and Mar 80 were too infrequent for a detailed analysis of change, but were used to check conclusions from the 1978 data. Figure 5.1.3 shows the change in exposure grade with season graphically for sites MG1 to MG11. For 1978, there appears to be a tendency for sites with an initial exposure grade of less than Grade 5.00 to become more exposed throughout the year, while sites with an initial exposure grade greater than Grade 5.00 tend to become more sheltered. Judging by the change between June 79 and Sept 79, the pattern seems to be repeated in 1979 with the exception of MG6 which shows an increase in exposure grade although its exposure grade is always less than Grade 5.00. The overall tendency, however, is for the exposure grade of a site to change towards the extremes of exposure or shelter. This change must be related to changes in species' maximum abundances throughout the year. For each site, the changes in species abundance between the seasons were summed to give figures of the total number of positive and negative changes throughout the year, as well as the total gross change in species abundance. These figures are given in Table 5.1.3, together with 129 Exposure Grade Figure 5.1,3 Change in Exposure Grade with Time for Mavis Grind (MG) Sites ThiB analysis was carried out for 1978 data only A Total No, Positive Changes in Species Abundances B Total No, Negative Changes in Species Abundances C Gross Total Changes in Species Abundances D Exposure Grade (May 78) E Gross Change in Exposure Grade f A B C D E MG1 32 54 86 4.75 0.75 MG2 22 36 58 5.75 2.50 MG3 29 33 62 7.50 0.75 MG4 35 44 79 7.50 0.75 MG5 17 35 52 7.50 0.75 MG6 26 39 65 4.50 1.00 MG7 22 25 47 3.50 0.25 MG8 9 24 33 2.00 0 MG9 8 22 30 1.75 0.25 MG10 21 27 48 0.50 0.25 MG11 9 24 33 0.00 0 Correlation Coefficients A B C D D 0.679 E 0.409 0.469 0.462 0.558 A significant correlation at p = 0,05 with v 9 is 0,602 Table 5,1.3 Correlations between Changes in Species Maximum Abundance and Exposure Grade correlation coefficients between selected sets of data. It can be seen that there is a significant positive correlation between the gross change in species abundance and exposure grade, there being more changes with more sheltered shores. This may be due to the fact that sheltered shores support a richer flora and fauna and there is thu a greater chance of changes in species* abundances occurring. In addition, species at sheltered sites have a lower resistance to wave action than species at exposed sites and would therefore be less likely to survive changes in this environmental variable throughout the year. Although there are more changes in species abundance on sheltered shores, reference to Table 5.1.3 shows that gross change in exposure grade at any site is not related to its actual exposure grade. From the limited number of sites studied, it seems that the gross change in exposure grade is also not related to the total positive or negative change in species abundance. The change in exposure grade must therefore depend on the balance in abundance between exposure and shelter indicators, and not on the total changes of all species present. For those species that are used in exposure grade determination, it was decided to look into individual changes in species maximum abundance more closely. The abundance of Verruccuria mucosa appears relatively stable throughout the year while the abundance of LicTrtna confin-is appears to change rapidly between seasons at three of the sites. This may be due to recording difficulties on dark, wet days when L-ichina does not stand out against the black lichens. As expected, the abundance of the fucoids and Ataxia escuienta remain very stable throughout the year. The percentage cover of healthy, pink "lithothamnia decreased throughout 1978, much of it appearing as a bleached and 132 dead covering by the end of the year. The abundance of Porphyra umbilioalis growing on Fuous serratus at MG7 dropped considerably between Aug and Nov 78. Gigartina stellata showed a gradual decline at MG1, MG2, MG4, and MG8, throughout the year, although there was a particularly large drop in abundance between Aug and Nov 78. More generally, Gigartina ste-llata and Chondrus orispus showed rapid fluctuations in abundance at most sites at any time of year. This may have partly been due to identification problems between the two species for very young individuals. Ceramium/Callithamnion increased at MG1 but decreased at MG4, being replaced by a spring increase in Gelidium pusillum at this site. Ectooarpus sp showed a marked season- ality, increasing in the spring but decreasing during the summer on the sheltered shores. On the exposed shores, Porphyra linearis was extremely abundant in the spring, but decreased to almost nothing during the summer. By Nov 78, sporelings were established at most exposed sites, but not at the most exposed site of MG11. The animals showed less predictable fluctuations. Balanus balanoides generally decreased throughout 1978 at the Sullom Voe sites of MG1 and MG2. There was also a decline at MG11. From 1979 and 1980 records, the barnacle population appears to have remained at the reduced level, thereby showing a change perhaps unrelated to the seasons. Barnacle abundance depends especially on the success of spatfall and the intensity of predation by dogwhelks. The abundance of Littorina littorea increased dramatically between spring and summer 1978 at a number of sheltered sites, and has remained at this higher level in 1979 and 1980, although it inexplicably declined at MG5. Littorina littoralis is uniformly extremely abundant at sheltered sites throughout the year, although its abundance fluctuates rapidly at slightly more exposed sites, showing a general decrease throughout the year. The abundance of Gibbula 133 cineraria decreased throughout 1978, particularly in the autumn. The abundances of Patella vulgata3 Mytilus edulis3 Spirorbis sp and Pomatoceros triqueter were generally stable throughout the year with changes occurring at perhaps one or two sites. An overall conclusion appears to be that many species show an increase in the spring followed by a decrease over the rest of the year. As a general statement, this may be due to the favourable conditions for reproduction and growth in the early part of the year being followed by unfavourable climatic conditions for the rest of the year. Wind speeds and maximum temperatures for Lerwick for 1978 were kindly supplied by The Observatory, Lerwick, and are shown plotted as a time-series in Figure 5.1.4. It can be seen that a period of high temperatures and low wind speeds was recorded for May 1978 which would result in calm waters and good drying conditions. It is likely that the dessication stress at this time of year was responsible for the reduced abundance of many algal species such as Porphyra linearis 3 and the noticeable bleaching of the "lithothamnia". A period of high winds was recorded for September 1978, and very rough sea conditions were experienced (W.J. Syratt, pers. comm.). Molluscs at moderately exposed sites may become dislodged in these conditions, and may be unable to return to the littoral zone. The increased wave action may also be responsible for the reduction in species such as Gigartina steltata at this time of year. The general pattern of species reduction throughout 1978 is probably typical for other years, as is demonstrated in Figure 5.1.5 where the temperature and wind speed conditions for 1978 appear to have been repeated for 1979. The general reduction in species abundance throughout the year is likely to have caused the tendency for the exposure grades for 1978 to change towards the extremes of exposure or shelter. Since the Figure 5,1.4 Wind Speeds and Maximum Temperatures at Lerwick in 1978 Annual Mean Wind Speed (l941rl97l) W«*p s«o> kts (Shetland Islands Council, 1978) k*v>. Figure 5.1.4 (cont) Wind Speeds and Maximum Temperatures at Lerwick in 1978 M OJ Ln Figure 5.1.4 (cont) Wind Speeds and Maximum Temperatures at Lerwick in 1978 u> vi Monthly Moan of Daily Maximum Temperatures °C Monthly Mean of Hourly Wind Speed Figure 5.1.5 Monthly Mean Temperatures and Wind Speeds for Lerwick 1978 - 1980. 139 standard abundance curves (Fiche 2) for most species appear to be unimodal and peaking at the middle of the exposure range, any reduction in the abundance of a particular species would tend to make the site appear more exposed or sheltered, depending on the original position of the site on the exposure gradient in relation to the peak of the curve. A similar explanation may be applicable to site MG2, which has been subjected to oil pollution. Table 5.1.2 shows that the exposure grade for this site increased from Grade 5.25 in Feb 78 to Grade 7.75 in Nov 78 and then decreased throughout 1979 to Grade 6.00 in Mar 80. It is likely that its true exposure grade is indeed around Grade 6.00 since this was the figure produced by considering the "strong species" alone in the exposure grading technique (see section 3.4). It would also appear to be a realistic value from a consideration of the fetch available for wave generation. Figure 5.1.6 shows the similarity curves for this site for the four recording periods in 1978. It can be seen that initially in Feb 78, there was a characteristic unimodal curve showing maximum similarity of species abundance to the standard abundances at exposure Grade 5.25. The whole curve becomes neater and shifts slightly towards shelter for May 78. By Aug 78 the peak has become broader over the sheltered range indicating greater similarity to a variety of grades. Nov 78 records show that the similarity to the middle of the exposure range drops away completely, leaving a maximum similarity at exposure Grade 7.75. Changes in the species maximum scores for MG2 may be observed in Figure 5.1.7. The topshore fucoids have shown considerable change since recording began. In Feb 78, Telvetia canaliculata and Fucus spiralis were abundant, although the individuals were mainly old and withered specimins. They gradually decreased in abundance throughout Feb 78 May 78 „ Aug 78 Nov 78 Coefficient of Similarity Exposure Grade Figure 5.1.6 Coefficient of Similarity vs. Exposure Grade for MG2 using Data Collected in 1978 141 V« mucosa . mm •f XV > c' ••: -v I I ' L. confinie .I..".'-.-....-- - "I•• • -- "I" Pelvetia j ; F. spiralis £ F. vesiculosus 'vi ::-.->.n *'T • V ' ' ' * '' o • ! • * fF, serratus t©o ; -8 o Ascophvllum © o L. digitata S • - f TT zn3i c • Lithothamnia J 3 Xi •J P^umbilicalis rr 6. 8tellata Ceramiunv/Callithamnion ss o P. lanosa o 1/3 I Corallina w o •I- .••v-*--^ I 5 B. balanoides _ Q Z • -• •- --i. j- rr § L. littorea -a! 3Z HH1 L, littoxalifl- i^ZHE •I:-- a Patella Ezmr nz Mytilus HE Z3I Spirorbis r Pomatoceros ' T I-••••I Jan 1978 Jan 1979 Jan 1980 Figure 5.1.7 Changes in Species' Maximum Abundances at MG2 1978 - 1980 142 1978 until many sporelings were noticed in June and Oct 79. Many of the se survived into Mar 80, thus slightly increasing the populations of these species over the Feb 78 abundances. It is likely that the original decline of these species was due to the oil since a characteristic flush of blue-green algae and Enteromorpha has been present over the winter and spring months above and within the Pelvetia zone. A typical recovery succession consists of the blue-green and green algal species followed by fucoid regeneration (Baker, 1976 b). On the lower shore, various species of red algae have shown significant reductions in abundance during 1978. The percentage of the rock covered by "lithothairnion" was considerably reduced, leaving areas of bare rock. Gigartina stellate Cevamium/Callithamnion and Corallina officinalis were also reduced. With the exception of CeYamium/Callithamnion3 all these species recovered slightly during 1979 and into 1980. Balanus balanoides abundance dropped during 1978 and has subsequently slightly recovered. The littorinids and Patella vulgata have had slightly reduced maximum abundances through 1978, and these low maximum abundances have remained constant into 1979 and 1980. The greatest effect of the oil has been seen in the range of these species. Although the maximum abundances have not been greatly altered, the midshore populations of L. li~ttoralis and Patella vulgata were almost absent by Nov 78. The general conclusion from records taken at site MG2 is that oil seeping into the voe has caused the species abundances to be reduced to unnaturally low levels throughout 1978. This accentuated the natural tendency for the exposure grades from sheltered shores to become higher (more sheltered) towards the end of the year. The species abundances and the exposure grades for 1979 and 1980 show that a recovery may have begun, even though oil was still visible at MG2 in March 1980. A report on the effect of oil pollution at Mavis Grind was sent to the Shetland Oil Terminal Environmental Advisory Group (SOTEAG) in that month. It appears as Appendix 6. 5.2 Annual Variation in Exposure Grade For biological monitoring purposes, OPRU have been recording the abundances of species at certain sites in May of each year since 1976. Their data were used in order to see whether the exposure grade of a particular site changes from year to year. The maximum abundance scores from sixteen of their sites were extracted from the raw data and are displayed in Appendix 2. Exposure grades were computed using program BALL 3 and are given in Table 5.2.1. It can be seen that for most sites the variation in exposure grade is no more than 0.25 or 0.50 unit of exposure over the four years of recording. For these sites, there appears to be no trend in the exposure grades, in that they seem to slightly increase or slightly decrease at random between years, irrespective of the initial exposure grade. However, five of the sixteen sites showed larger changes in •r^posure grade between years, which were worthy of further investigation, The exposure grades for OP56 varied erratically between Grade 6.00 and Grade 7.75 while those for OP59 varied erratically between Grade 5.75 and Grade 9.00. These two sites are on highly particulate substrates, and the variability in the biological estimate of exposure grade is probably due to the fact that some species would be abundant in some years and not in others depending on the mobility of the substrate. Also, seaweeds attached to very small stones may occasionally be washed away from the transect to cause abundance records to fluctuate between years. It has already been observed in section 4.4 that particulate substrates do not produce reliable estimates of exposure. Site Name 1976 1977 1978 1979 0P73 West of Mioness 2.00 1.75 2.25 1.50 OP67 Skaw Taing 2.50 2.50 2.50 2.75 0P65 Roe Clett 2.50 2.75 2.75 2.50 OP71 Ay Wick 2.75 3.00 3.00 2.75 0P68 Skaw / Swarta Taing 3.50 3.50 4.00 4.00 OP54 Burraland 3.50 4.00 4.00 3.75 0P52 Gluss East 3.00 3.00 2.75 2.75 0P70 South Swarta Taing 3.50 3.75 3.50 3.50 0P69 Swarta Taing 4.00 4.25 4.50 4.50 0P51 Grunn Taing 4.00 4.25 4.00 4.00 j OP 63 The Karnes 4.00 4.50 3.75 4.00 1I j 0P58 Voxter 4.50 4.75 4.00 3.25 0P66 South Skaw Taing 4.75 4.50 4.75 4.75 0P59 Scatsta 7.75 5.75 7.00 9.00 0P57 Maris Grind East 6.50 6.75 6.50 8.00 0P56 Sullom Pier 7.00 7.75 6.00 7.25 Table 5.2.1 Annual Exposure Grades from Selected QPRU Sites 145 Other sites which have large changes in exposure grade appear to be stable between 1976 and 1978, the anomalous grades occurring from the 1979 data. The exposure grade for OP57 increases rapidly from about Grade 6.50 to Grade 8.00, while that for OP58 decreases from about Grade 4.50 to Grade 3.25 and that for OP73 decreases from about Grade 2.00 to Grade 1.50. The fact that the sheltered shore grade becomes more sheltered and the exposed shore grades becomes more exposed implies that reduced species abundances are recorded for"1979. This is certainly the case for OP58 where many species apparently disappeared before the 1979 survey - notably Laminaria digitata3 Gigartina stellata, Chondrus crispus3 Gibbula cineraria3 Sprirorbis sp. and Pomatooeros triqueter. From the raw data sheets, it seems likely that this site was visited when the tide was not at the recommended spring low tide level, although this fact was not commented upon in the report (Hiscock et al, 1979). The 1979 exposure grade for 0P58 may therefore be based upon insufficient data. It seems that the exposure grade for OP57 becomes higher (more sheltered) for 1973 through more subtle, changes in recorded population levels, but aiding these may be the apparent lack of Porphyra umbilicalis and Chondrus orispus recorded in the 1979 survey. The change in exposure grade at OP73 from Grade 2.25 to Grade 1.50 seems to occur because of large recorded changes in abundance. Ataria esculenta (an exposure indicator) increases from common to extremely abundant, while counteracting this, Littorina UttoraZis (a shelter indicator) increases from absent to frequent. However, the two shelter indicators of Spirorbis and Pomatoceros triqueter decrease from frequent to absent between 1978 and 1979, thereby perhaps explaining the decrease in exposure grade. It must be appreciated that in each of the years from 1976 to 1979, the transects have been recorded by different personnel. Due 146 largely to a subjective element in the abundance estimates, this may mean that worker variability may account for some of the apparent variation in abundances of species. This has in fact been commented upon in one of the OPRU reports (Baker et al., 1977), although as stated by Hiscock et al (1978), the abundance measurement technique has been improved in order to reduce subjectivity. At this stage, it must be pointed out that the large changes in species abundances between 1978 and 1979 for sites OP57 and OP73 could not be due to oil pollution from the Esso Bernicia spill (January, 1979), since no oil was recorded from these shores. It seems more likely that a combination of worker variability and natural species changes are responsible for the changes in exposure grade at these sites. In conclusion, the exposure grades from eleven of the sixteen sites are reasonably constant over the period 1976 to 1979. Anomalous exposure grades for three sites are explicable, leaving only two sites where recorded species changes have greatly altered the exposure grade for one of the years. Apart from these two sites, it would seem that the exposure grading technique adequately integrates natural fluctuations in population density to produce a reasonably constant estimate of wave exposure. 147 CHAPTER 9 The Shetland Exposure Scale - Summary The biological exposure scale developed by Dalby et al (1978) for shores in Western Norway was applied to sites in Shetland. It was soon realised that the Norwegian scale could not be directly applied, to Shetland because of ecological differences between the two areas. Also, it was apparent that more exposed sites had been encountered in Shetland, and that this would require an extension of the scale. Using various aids, the Shetland sites were grouped into whole units of exposure ranging from Grade 0 (exposed) to Grade 9 (sheltered). Further computations in the development of the new scale followed the pattern used by Dalby et al (1978). Although it was clear that the new Shetland exposure scale produced representative estimates of wave exposure, it was appreciated that different methods could have been used in the collection of data and subsequent analysis. The effect of using an apparently more precise abundance measurement technique was investigated, but the results using this method were virtually the same as those produced by the original, less laborious technique. It was realised, in fact, that the original technique could probably be streamlined in that only the maximum abundances of a reduced species set need be recorded. Several species sets were used, and predictably the most reliable consisted of those species that respond most sensitively to the exposure gradient. In using the species maximum scores, it was realised that the selection of the appropriate vertical interval on the shore was important in determining the area of each station that needed to be surveyed for abundance assessment. In a marginal case, the tolerance of the exposure grading technique was demonstrated in that the selection of different 148 vertical intervals did not influence the exposure grade. In the preparation of the exposure scale, two abundance smoothing cycles were used to produce standard species abundances for each grade of exposure. The effect of using more cycles was investigated, but found to produce less representative estimates of wave exposure. Having tested the use of different techniques for producing and using an exposure scale, it was decided to investigate the environmental limits to which the exposure scale could be applied. Various environmental variables were measured at each site which could be categorised as either being "exposure factors" or secondary physical factors. The exposure factors were shown to be directly related to the exposure grade, and indeed, it was possible to produce exposure grades close to the biological estimates from three exposure factors alone. By looking at the difference between the observed and the expected exposure grade, it was possible to examine the influence of the secondary physical factors in causing the observed grade computed from a biological exposure scale to deviate from the expected exposure grade calculated from physical exposure factors. As also predicted from statistical analyses, the particularity factors had the greatest secondary influence on the exposure grade that was assigned to a shore. Limits could be set on the reliability of the exposure scale when applied to shores having different substrates, angles of slope, Roughness Ratios, and degrees of fissuring. On the whole, the exposure scale appeared to be reliable over a wide range of shore types. In order that the exposure scale should give a useful estimate of the wave exposure status of a site, it should not only be applicable to a wide range of shore types, but it should also produce a reasonably constant grade both seasonally and from year to year. It has been 149 shown that both seasonal and longer term trends in plant and animal populations do little to influence the overall exposure grade of the shore. This is presumably due to the integrating nature of the exposure grading technique in that changes in one species are likely to be offset by changes in another. In conclusion, the biological exposure scale developed for Shetland appears to produce a realiable estimate of the position of a site on the wave exposure gradient. Furthermore, this estimate of the wave exposure status of a site represents an integration of the wave conditions over the lifetime of the organisms present on the shore. In most cases, this is likely to be several years. PART III MEASUREMENT OF WAVE ACTION 150 CHAPTER 9 Measurement of Wave Action - Introduction The biological exposure scale developed for Shetland has been shown to provide a reliable framework against which the wave exposure status of a site may be categorised. Furthermore, by using species' abundances, the exposure grade assigned to a shore can represent the integration of wave pressures over several years. However, it was recognised that the formation of the exposure scale involves a certain amount of subjectivity in initially assigning a particular grade of exposure to a shore. This initial assessment is based partly on physical indicators of wave exposure, but mainly on biological con- siderations with the assumption that the ecology of the shore is primarily related to the amount of wave action. This assumption is part of a circularity in the argument which could be resolved with more information on the physical basis of the exposure scale provided by measurements of wave action. This would enable the exposure scale to be used more confidently when applying it to different geographical areas and would also allow proper separation of the grades oh the scale in terms of a direct measure of wave action. Variuos components of wave action have been measured in the past, mainly in connection with engineering studies. The early work of Stevenson (1849) has already been mentioned. He developed a dynamometer which consisted of a structure similar to a railway buffer that was attached to a shoreline or breakwater such that the total impact pressure of the waves could be measured. Initially, only maximum pressures over a given duration could be recorded, but later instruments included a drum worked by clockwork such that the pressure of every wave could be recorded (Hiroi, 1920). It is likely that mechanical devices such as these are limited in their response for the recording of short duration 151 events. For this reason, accurate measurements of the pressure fluc- tuation during each wave were not possible, and early field measure- ments only recorded the maximum pressure. However, measurements from the mechanical type of dynamometer provided useful information on the overall wave pressures experienced by fixed structures (Molitor, 1935). Gaillard (1904) considered a wide variety of devices for estimating wave action in relation to engineering structures. These included the breaking of columns of different strengths and the moving of blocks of material of different weight. He also used dynamometers of various types, some of which transmitted the movement of the force-collecting plate to a recording site using hydraulic fluid. Various electrical systems were also employed in order to provide more precise information on the pressures due to wave impact. Some of these instruments were developed by de Rouville et al (1938) for use at various sites in France, The first of their hydraulic designs consisted of a pressure plate connected via a tube of liquid to a pen recorder. Because of problems caused by mud and water seeping in behind the plate, this design was modified by replacing the plate with a sealed but flexible diaphragm. It was thought that this form of dynamometer would continuously record hydrostatic and dynamic forces with some accuracy, although its inertia would limit its usefulness in the recording of short duration events. In order to improve the response time, various electrical systems were tried, the most useful of which consisted of a quartz piezoelectric sensor connected to a photographic recording system. Amplified impulses from the sensor turned a mirror which reflected a light beam on to a roll of photographic paper. Various arrays of the sensors were installed on harbour walls at Le Havre and Dieppe. Using the equipment carefully, de Rouville et al recorded high intensity, short duration shock pressures at the beginning of some wave impacts. Each shock only lasted about 0.005 second and occurred very infrequently. The 152 2 maximum pressure cited in de Rouville et al (1938) is 69 tonnes / m (98.14 PSI), recorded from the lowest sensor on the array on the harbour wall. The precise nature of shock pressures was investigated in the laboratory by Bagnold (1939) using equipment similar to that used by de Rouville et al (1938). Bagnold's system consisted of a quartz piezoelectric sensor connected through an amplifier to a cathode ray oscillograph. Breaking waves were generated in a wave tank so that there was a high probability of shock pressures occurring. This was most likely when the wave enclosed a small pocket of air as it broke against the artificial shore. Shock pressure intensity varied almost at random, although it tended to increase with a decrease in the thickness of the enclosed air cushion. Increasing the probability of shock pressures occurring tended to increase the maximum pressure obtained up to an overall maximum of about 80 PSI, obtained from waves no more than a couple of feet in height. Extrapolated to field conditions, enormous shock pressures might be expected, but as Denny (1951) and Defant (1961) point out, the shock pressures of the magnitude expected by Bagnold's work would be unlikely (or at least extremely rare) in the field due to irregularities in the waves' form. More recent studies of wave pressures have employed either a piezoelectric crystal or a strain-guaged diaphragm as the basic sensing unit. Many different supporting structures and ancillary equipment have been used depending on the location of the sensing element. The most common places are either in a laboratory wave tank or attached to a structure in the field - examples include oil rig legs, and sluice gates. Weigel (1956) and Coastal Engineering (1960, 1974) give a good summary of a number of designs used in these specific locations. There is very little recently published work on wave pressures 153 encountered on the natural shoreline. Miller et al (1974 a, b) tried to redress this deficiency by designing a portable electrical system for use in the field. They mounted five strain-guaged diaphragms on a vertical pole that was fixed on a shallow sloping tidal flat. An- cillary equipment (apart from the amplifiers) was housed above high tide level. Power was supplied to the sensing elements by a generator, and the returning signal was recorded on an oscilloscope equipped with a Polaroid camera. They found that the pressure trace of each wave depended upon the breaker shape and the tidal level in relation to the sensing element. The background shape of the trace was generally uniform, but the magnitude of the superimposed shock pressures showed some variation. Various formulae have been developed in order to calculate the forces of waves against a structure for the purposes of design (U.S. Army, 1966). The forces to be considered would appear to depend upon the wave type. In sheltered areas, non-breaking waves may be expected in which the main forces are essentially hydrostatic in that they are related to the weight of water provided by the wave height. Breaking waves cause both static and dynamic pressures which form a wave impulse very similar to that caused by non-breaking waves. In addition, howevei, there may be the short duration, high intensity shock pressures at the beginning of the impulse as studied by Miller et al (1974 a, b) . Jones and Demetropoulos (1968) pointed to further wave forces which may be ecologically important in considering a measurement of wave action. In addition to the shock, static and dynamic wave pressures, the move- ment of water across the rock and plant and animal surfaces will cause a drag force which is proportional to the velocity of the water. The drag force is likely to be important in dislodging organisms from the rock, particularly in their juvenile stages. Abrasion is another 154 component of wave action which might influence the ecology of the shore if there is a large amount of loose material in suspension. Fine particles picked up by waves would have a scouring action in addition to other effects such as interfering with the filter feeding of animals such as barnacles. However, abrasion of this kind is likely to be an indirect effect of wave action applicable, in Shetland, only to the more sheltered rocky shores. Abrasion caused by the more flexible algae being washed against the surrounding rock surface might be important in that it would cause individuals to become rather damaged, but is unlikely to cause reductions in overall abundance except on the most exposed rocky shores. Observations on AZaria esoulenta in gullies shows that the morphology of the more flexible algae is such that they bend so readily with a change in the direction of water flow that they rarely hit the rock surface. Indeed, growth appears to be enhanced in these conditions. It was clear that the measurement of drag forces and seaweed abrasion would require instruments different from those that would be used to measure the shock, dynamic and static wave impact forces. Sincc the relative ecological importance of these components of wave action was not known, it was decided initially to measure wave impact pressures since the other components of wave action would be directly related to these. The drag forces depend upon the velocity of the water sweeping across the rock and this itself is likely to depend upon the static and dynamic wave pressures, and perhaps also upon the existence and magnitude of shock pressures. The extent to which seaweeds would be abraded against the rock would also depend upon these same wave impact pressures. CHAPTER 8 Wave Pressure Measuring Equipment 8.1 Selection Criteria In devising appropriate instrumentation, some idea of the magnitude and duration of wave pressure events was required. Previous field measurements of wave pressures have been made using a variety of different instruments producing results expressed in many different units. An attempt has been made in Table 8.1.1 below to summarise the maximum wave impact pressures that have previously been recorded: Author Max Impact Pressure Approx PSI Stevenson (1849) 3369 lbs/sq ft 25 Hiroi (1920) 50 lbs/sq in 50 Moiltor (1935) 2370 Ibs/sq ft 20 Gaillard (1904) 0.325 kg/sq cm 4 de Rouville (1938) 69 tonnes/m2 100 Miller (1974) 5.85 PSI 6 Table 8.1.1 Maximum Wave Pressures Previously Recorded The maximum impact pressures were presumably produced by the shock pressure element of the total wave force. As shown in the table above, these may have a pressure in the order of 50 PSI or even 100 PSI, and act over a period as short as 0.001 second (Bagnold, 1939). At the other end of the scale, my own observations of sheltered shores in Shetland have shown that typical wave heights for non-breaking waves may be as low as 5 cm, which corresponds to a hydrostatic pressure of only 0.07 PSI. In order to record this range of wave pressures adequately, the instruments would need to be flexible with provision for plenty of amplification of low intensity pressures. The equipment would also need to have a fast response time and sufficient range in order to be able to record the high intensity, short duration shock pressures. In addition, the equipment needed to be fairly cheap, light, robust 156 and easily transportable to a shoreline site where there was no poss- ibility of mains power. The initial aim was to record wave pressures simultaneously from four adjacent sites around a headland. The maximum separation of the sites was about 100 m., and so it seemed desirable to have four sensing elements connected to a central multichannel recorder via a cable length of approximately 60 m. for each sensor. The sensors would need to be completely waterproof and as small as possible so as not to interfere with the wave impact on rock surfaces. The sensors would also need to have a high output such that the signal would not be greatly reduced by the resistance of 60 m. of cable. In view of the isolation of the fieldwork site from the laboratory, a further requirement was that the equipment should provide a permanent record that could be viewed instantly and studied later in the laboratory. 8.2 The Equipment Described The sensing element that was selected was a pressure transducer manufactured by Kulite Sensors Ltd., and marketed as a "Soil Pressure Cell Type 0234". It was designed for the measurement of soil stress, but exhibited all the qualities required for this application. Its external appearance (Plate 8.2.1) is that of a flat disc 8 mm. in thickness and 55 mm. in diameter, with a cable port in the side of the disc. This was convenient in that the transducer could be mounted flat on to a backing plate using four threaded holes in its underside. It was thought that this flat assembly would minimise any shedding of the wave impact and would be subjected to similar pressures to a rock surface. The body of the transducer is made out of stainless steel and would therefore not corrode in seawater. The top surface is covered by a protective layer of silicon rubber under which there is a thin foil force collecting plate (Plate 8.2.2). This covers an oil filled cavity through which pressure is transmitted to the actual sensing 157 Plat© 8.2.3 Damaged Pressure Cell Plate 8.2.4 Close-up of View Under Force Collecting Plate Semiconductor Header 158 element which is a silicon semiconductor strain guage (Plate 8.2.3) (Kulite Semiconductor Inc., n.d.). Drawings showing this arrangement in more detail are given in Figure 8.2.1. The silicon semiconductor uses the piezoresistivity principle in that the silicon is doped with impurities in certain areas to increase its natural change in electrical resistivity with applied stress. The doping is applied to four areas on a traditional Timosherko clamped edge diaphragm to produce guages in tension and compression linked together to form a Wheatstone Bridge circuit (Window, 1971). The wires involved are faintly visible in Plate 8.2.4, and are diagrammatically illustrated in Figure 8.2.1. The Wheatstone Bridge circuit is useful in that it provides a simple means of measuring small changes in resistance with a high degree of precision. With no stress, the bridge resistances should be in balance, and no current should be able to flow through the output. A small stress would throw the bridge out of balance, allowing a certain amount of the input to be detected through the output. The fact that the resistances consist of doped silicon means that the possible output voltage is relatively high and the frequency response is almost instantaneous. Indeed, the limitations on the frequency response of the whole instrument would be provided by the force collecting plate and oil filled cavity. Although the frequency response of the whole instrument was not known, it was thought to be adequate for this purpose. In the case of the Kulite Soil Pressure Cell, the Wheatstone Bridge circuit is completed behind the silicon semiconductor by means of resistors Rp and Rs (see Figure 8.2.1). The resistors provide a method for compensating the bridge for any change in resistivity due to temperature changes (Kulite Semiconductor Inc., n.d.). The Kulite Soil Pressure Cell was available to cover ranges 0-2 bar (approx. 0-30 PSI) or 0 - 7 bar (approx. 0 - 100 PSI). In each 159 Diaphragm Foil Header Silicon Force-Collecting / Oil-Filled Rubber Plate / /Cavity A— Waterproof Stainless Resistor Sealant Steel Body Cross-section of Soil Pressure Cell Plan of Shoving Positions of Diaphragm Doped Areas of Silicon Circuit Diagram of Classic Wheatstone Bridge Circuit Soil Pressure Cell • OUT — OUT ON | BEHIND DLA PHR AGM Figure 8.2.1 The Soil Pressure Cell 160 case, the input voltage required was 10 V. D.C. and the full range output was nominally 100 mV. In order to ensure an adequate output for the smaller wave pressures, the 0-2 bar instrument was selected, with the initial aim of not using the instruments on the most exposed shores. Although the lower range instrument would only record 0-30 PSI, the specification states that the instrument could survive up to 60 PSI with no damage. The complete specifications for the Soil Pressure Cell as supplied by Kulite Sensors Ltd., are given in Appendix 7. Initially one, but later three more, transducers of this type were purchased. A special requirement of the order was that 60 m. of a heavy duty waterproof cable should be attached to each transducer. The necessary cable consisted of four wires surrounded by a screen and a thick rubber coating. In order to provide a waterproof join with the transducer, a special adaptor was made by Kulite Sensors Ltd., so that the thicker cable could join in to the narrower cable port on the side of the instrument. The multichannel chart recorder that was selected was the BHL 5000 Minigraph, manufactured by Bell & Howell Ltd., (Plate 8.2.5). It has an extremely fast writing speed because the writing instruments are mirror galvanometers that reflect a light beam on to light sensitive paper. BHL 7-383 galvanometers were used in the instrument to give a writing speed in excess of 400 m/sec which would record rise times of less than 100 microseconds (Bell and Howell Ltd., n.d.). This was considered adequate to measure shock pressures during the wave impact. The light source is a 20 W tungsten halogen lamp. The reflected beam / is recorded on to direct print photographic paper available in 30 m. rolls from Kodak or Agfa. No development of the image is necessary, but it does fade if exposed to bright sunlight. The paper may be run at speeds ranging from 1 mm/s to 1 m/s, and up to eight channels of 161 Plate 8.2.5 Recording Instruments in Hut Left : Chart Recorder Centre j Signal Conditioning Module Right : Battery information may be recorded simultaneously. The galvanometers require 2.5 mA/cm of deflection and the overall power consumption of the instrument is only 4 A on a nominal 12 V battery. More precise specifications as supplied by Bell and Howell Ltd., are given in Appendix 7. At this stage it was clear that the whole system could be run from a 12 V portable battery. However, the power supply to the transducers required regulating and the signals from the transducers needed to be made compatable for the chart recorder. An appropriate instrument was available from Bell and Howell Ltd., in the form of the BHL 5107 Resistance Bridge Conditioning / Amplifier. One of these was required for each transducer, and so a case of four was supplied as illustrated in Plate 8.2.5. This constituted the. signal conditioning module. The BHL 5107 is an extremely versatile instrument (Bell and Howell Ltd., n.d. as shown by the specifications in Appendix 7. Its capabilities in relation to this application are best demonstrated in a description of the setting up of the complete system of instruments. An Oldham's "Carefree" 12 V, 30 ampere-hour, rechargeable battery was used to power the instruments (Plate 8.2.5). It has a long life and was considered to be safe for transport in that it is completely sealed and there is no access to acid. A wiring system was made up to run from the battery to a control box and from the control box to the recorder, the signal conditioning module and a light. The cables from each transducer were plugged into each channel of the signal conditioning module, and each channel of the signal conditioning module was connected to a galvanometer in the recorder. The whole system is shown diagranmatically in Figure 8.2.2. In order to fix the power supply into the transducer, an Avometer 163 n BATTERY POWER SUPPL Y Signal Conditioning AMPLIFIER Module ii ii II 60 m. < f ii M CHART ii »l RECORDER J Hut PRESSURE TRANSDUCER Figure 8.2.2 Flow Diagram of Wave Pressure Measuring Equipment 164 is connected across two bridge voltage check points on the BHL 5107, and the power supply is adjusted by means of a screwdriver operated control. The resistances in the Wheatstone Bridge circuit of the transducer are balanced by a coarse and fine control on the BHL 5107. Balance is in- dicated by two L.E.D.s which should flicker when complete balance has been obtained. The zero position of the galvanometer beam is then located on the recorder display by physically moving the galvanometer mirror and by using a shift control on the BHL 5107. The required full scale deflection of the beam is then set using a scale control. This then scales the output from the gain controls so that the transducer output is compatable with the galvanometer sensitivity. In practice this means that if the transducer has a full scale output of 90 mV, and the gain control on the BHL 5107 is set at 90 mV, then the full pressure range of the transducer will be seen on the centimetres scale set by the scale control. If the gain control is then set at 9 mV, the signal from.the transducer is amplified by a factor of 10, because only 9 mV will then be seen on the same centimetres scale. Any amplification may be set corresponding to a range on the gain control from 1 mV to IV. 8.3 Initial Field Trials Before the complete system was purchased, it was decided to try one channel of the equipment in order to see that it did indeed respond to wave pressures as predicted. One Kulite Soil Pressure Cell with 60 m. cable was purchased, and a signal conditioning module and chart recorder were borrowed from Bell and Howell Ltd. A perspex backing plate (250 x 100 x 10 mm.) was made for the transducer such that a cable clip could be incorporated close to the cable's join to the transducer (as in Plate 8.2.1). This was to prevent water currents from pulling the cable and weakening the joint. The backing plate itself was anchored to the rock by means of various "bolts" 165 as used by rock climbers (Figure 8.3.1). Each bolt is a cylinder with a star-shaped drill bit at one end and a threaded interior at the other. A "driver" is screwed on to the threaded end so that it can be tapped and turned while the star drill on the other end bites into the rock. When a suitable hole has been made, the "driver" is removed and a cone is inserted into the drill bit. By hitting the bolt into the hole, the cone splays out the drill bit so that it grips the sides of the hole and provides a firm anchorage for anything that is attached to the threaded end. The equipment for trial was taken to the Field Studies Council's Dale Fort Field Centre in Dyfed, South Wales. Dale Fort was considered useful for field trials because it is situated immediately above the shoreline at the end of a narrow headland jutting out into Milford Haven (Figure 8.3.2). This was also the area where Ballantine (1961) collected data for his biological exposure scale. The equipment was firstly installed on the more sheltered side of the headland at Dale Fort Pier where Ballantine estimated the exposure of the shore to be Grade 6.00 on his eight point scale. This site was convenient because the recording part of the equipment could be kept in a van on the pier, while the transducer was bolted to a rock at approximately mid-tide level. The equipment was deployed for a number of tidal cycles over two days in which the wind blew strongly from the north-west. Swell was minimal, and the wave environment was dominated by steep wind driven waves approximately 0.5 m. in height. As the tide rose up to mid-tide level, spikes appeared on the chart when water splashed on to the transducer. The complete wave form did not appear until the waves were impacting fully upon the transducer. The most useful period to record was considered to be from this moment until the baseline between NORMAL BOLT Threaded End CLIMBING BOLT Star-Drill End CONE Figure 8,3.1 Details of a Climbing Bolt 167 Figure 8.3.2 Location of Testing Sites at Dale Fort, Dyfed 168 waves disappeared and the transducer was completely submerged. Between these limits, a complete range of amplifications and recording paper speeds were used, representative samples of wave trace being shown on Plates 8.3.1 and 8.3.2. It can be seen that impact pressures ranged from 0.1 PSI to 0.25 PSI, and that shock pressures frequently occurred on the rising limb of each wave form. These appeared to be adequately recorded within the capabilities of the instruments. The fact that they sometimes dropped below the baseline was not expected and con- sidered worthy of future investigation. The equipment was also installed on the other side of the headland at Dale Point where Ballantine estimated the shore to have an exposure grade of approximately Grade 3. In this case, the van could not be driven close enough to the shoreline, and the recording instruments had to be carried part of the way down the cliff for each recording session. Unfortunately the sea was extremely calm over this period, and the maximum rise and fall of the swell was only about 0.5 m. There were no wind driven w;aves and it was thought that most of the wave pressure was caused by the hydrostatic head of water above the trans- ducer as the wave passed over it. The shape of the wave trace is shown in Plate 8.3.3. Despite the rather unsatisfactory testing conditions, it was thought that the instruments performed well, particularly in responding rapidly to shock pressures. The field trials had shown that it was safe to proceed with purchasing the complete system for use in Shetland. However, they had also highlighted certain deficiencies in ancillary equipment. It was clear that a stronger backing plate was required, and also that the cable needed anchoring firmly to the rock at intervals up the intertidal section of the shore. It also seemed desirable to protect the cable from abrasion. These requirements had to be met before the equipment was taken up to Shetland. 169 17 OCT 78 DALE FORT PIER RISINU TIDE PAPER 5 nun/sec AiiP 2 K Waves hitting transducer Plate 8.3.1 Wave Trace from Dale Fort Pier - 5 mm/s III!'11 1 17 OCT 78 DALE FORT PIER RISINU TIDE PAPER 100 mm/sec AMP 2 K Definition of shock pressures Plate 8.3.2 Wave Trace from Dale Fort Pier - 100 mm/s PSI 0.264 0.210 0.156 0.104 0.052 Plate 8.3.3 Wave Trace from Dale Point - 5 mm/B 170 CHAPTER 9 Data Collection at Mavis Grind, Shetland The configuration of the coastline around Mavis Grind, North Mainland, Shetland has already been described in Section 2.4. Its physical characteristics are illustrated in Figure 9.0.1. With the aim of obtaining simultaneous wave pressure measurements from sites of different wave exposure, two areas at Mavis Grind seemed suitable. To the west of Mavis Grind, Culsetter Voe is separated from the open sea of St. Magnus Bay by a narrow inlet (minn) caused by two projecting headlands. These produce a rapid but regular change in exposure as described by the exposure grades of MG9 - MG6 (Grade 1.75 - Grade 4.50) on the north shore of the minn. Simultaneous measurements of wave pressures could be obtained from these four sites by installing the transducers around the headland and connecting them to the recorder situated centrally. For more sheltered conditions, it seemed that the short distance across Mavis Grind itself would provide another location where simultaneous measurements of wave pressures could be obtained from sites adjacent to MG2 (Grade 5.75) in Sullom Voe and MG3 (Grade 7.50) in Culsetter Voe. At each of the sites it was considered useful to be able to estimate the dominant wave height. At most sites this could be done with a ruler or the cross-staff held vertically in the water at fixed points, but special apparatus was required for MG8 and MG9 in St. Magnus Bay where the wave heights could be very large. At the two recording locations (MG6 - MG9 and MG2A-MG3A), it was also considered useful to record wind speed and direction. 9.1 Calibration of the Wave Pressure Measuring Equipment Calibration certificates were supplied with each of the transducers FIGURE 9.Q.1 Location of Wave PP«SSUP® RaeordiNG Sitaa and Equipment at Mavis Grind H VJ 72 in which the maximum output in millivolts was specified for full scale deflection. Assuming linearity, the recorder and signal conditioning module could be set up so that a direct interpretation of the wave traces in terms of PSI could be applied. In order to check the calibration throughout a range of pressures, each transducer was lowered into water in depth stages corresponding to each unit of pressure from 1 PSI to 30 PSI. According to the Handbook of Oceanographic Tables (1966), the pressure of seawater increases by 0.445 PSI per foot depth of water in the North Atlantic. Depths corresponding to each PSI were calculated, and it was realised that 20.57 m. of water were required to exert a pressure of 30 PSI, full scale for the transducers. In view of the large depth of water required, one of the Tanker Loading Jetties at the Oil Terminal seemed to be the most suitable place to conduct the calibration. Permission was granted for access to Jetty No. 3 which was under construction at the time of the study (May 1979). Each transducer was lowered off the end of the jetty to various depths through the pressure range 0-30 PSI. At each depth, the recorded pressure was exactly as expected, and the deflection response was indeed linear. With this increase in confidence, the equipment was ready for installation at Mavis Grind for the accurate measurement of wave pressures. 9.2 Recording at MG6 - MG9 All the equipment required for recording at MG6 - MG9 was trans- ported from the road at Mavis Grind to the site using a Zodiac inflatable boat borrowed from the oil terminal authorities. The largest item was a dismantled hut that had been built by the Botany Department workshops at Imperial College to a special design (see Figure 9.2.1). It was made as small as reasonably possible so that the battery, signal conditioning PLAN 1.50 m. ELEVATION Figure 9.2.1 Details of Hut 74 module and recorder would fit at one end while there was room at the other end for a person to squat in the hut and adjust the instruments protected from the rain. Two doors were provided in opposite walls at this end such that there was a good chance that one of the doors would be leeward to the wind at any time. The doors were provided with plenty of fastenings so that they would not be caught by the wind. Large, strong screw-eyes were attached to each corner so that guy ropes could be used to hold the whole structure down and prevent it from being dislodged during gales. An exit for the transducer cables was provided via an angled rubber pipe through a hole in one of the walls. The hut was made of exterior quality ply wood on a pine frame. The topside of the roof section and the underside of the floor section were covered with roofing felt, while the rest of the structure was protected with several coats of varnish. For ease of transport, the hut could be dismantled by simply undoing a number of coachbolts and breaking the structure down into wall sections, the roof and the floor. Once the hut was assembled, installation of the transducers could begin. The first transducers to be installed at the end of May 1979 had the following serial numbers: 2856, 2857, 2858, 1937. Their cal- ibration certificates appear in Appendix 7. Approximately the lowest 20 m. of cable to each transducer was protected from abrasion by inserting it into a split length of garden hose. Subsequent wear of the hose against barnacles and sharp edges showed this to be a wise decision. Each transducer was then attached to a stainless steel backing plate (250 X 100 X 10 mm.) which was also provided with a clamp for the end of the hosepipe containing the cable. The backing plate was initially attached to the shore by means of a single "climbing bolt" as described in section 8.3. On MG8 and MG9, stainless steel tabs were attached to the shore with "climbing bolts" at intervals above the transducers such that they 175 could be bent over the hose to provide anchorage. Transducers were attached to MG6, MG7, MG8, and MG9 at mid-tide level on selected open areas of rock having a constant slope of about 30°. The cables from the transducers were led up the shore into the hut and connected into the signal conditioning module. The battery and chart recorder wer also wired up in the hut. The battery was strapped into a rucksack - style carrying frame that had been specially made by modifying a crop spraying "rucksack" with pieces of Dexion "angle-iron". This was because it was necessary to carry the battery back to a power source for recharging after every other recording session. A cup anemometer was installed near to the hut on the top of the headland so that it would be open to winds from most directions. The location of the anemometer in relation to the hut and transducers is shown in Figure 9.2.2 and illustrated in Plate 9.2.1. Plate 8.2.5. shows the recording instruments installed in the hut, and Plate 9.2.2. shows the position of a transducer on its backing plate on MG8. Wave height was estimated at a fixed point between MG6 and MG7 using a ruler or the cross-staff held vertically in the water. Because of the larger wave heights at MG8 and MG9, a variety of methods were used to estimate wave height on the St. Magnus Bay side of the minn. Originally, a wave staff that had been used by R. Dockworth of British Petroleum for measuring wave heights on reservoirs was modified for use in the sea. The wave staff consisted of a 6 m. vertical steel pole with a 0.5 m. diameter buoy located in a central position. One end of the pole was provided with links so that it could be anchored to the bottom of the lake so that the buoy was submerged but holding the pole vertically upwards through the water surface. For ease of transport to Shetland, the pole was cut in to 2 m. sections, and further sections 176 m. above C.D. Scales 2 cm. - 10 m. \ \ 21 r N X y II* ANEMOMETER V X y \ / ROPE TO WAVE STAFF ATLANTIC OCEAN Figure 9.2.2 Location of Wave Pressure Measuring Equipment at WG6-9 Plate 9,2.2 Transducer and Hosepipe containing Cable on MG8 ——————————— t 178 were obtained to allow for the larger wave heights that would be expected in the sea. The top sections were graduated at 0.1 m. intervals. To counteract the extra weight of the added sections, an additional buoy was used in the central section. In order to be able to compensate for the tides, a long length of rope was attached to the bottom end of the wave staff so that it would go through an eye-piece in the anchor and thense to an attachment point on the shore. This would provide the facility for raising or lowering the wave staff to suit conditions. The final form of the wave staff is shown in Figure 9.2.3. Initially, the wave staff was located approximately 20 m. offshore from MG9 in about 12 m. of water. A section of 'I' beam estimated to weigh about 100 Kg. was used as an anchor and transported to the site using the Zodiac. Over the recording period, wave height was estimated from the wave staff using binoculars. When estimation was difficult, the waves were filmed against the staff using a zoom lens on a cine camera. The wave staff appeared to function well until the wave height exceeded about 0.8 m. when it would tend to ride up and down with the waves, leading to underestimates of the actual wave height. When this was realised, a graduated scale was painted on a vertical piece of rock on the opposite shore to MG8 and MG9 during the next period of calm conditions at low tide. Estimates against this scale tended to overestimate wave height because the water in the wave would surge up the rock. With experience, the recorded wave height was taken as a rough mean of the estimates from the wave staff and the rock scale. The first period for wave pressure recording at MG6 - MG9 was from 30 May 79 to 27 June 79 when traces numbered from 1 to 28 were obtained. Usually one set of measurements were taken per day on either a rising or falling tide, depending on which was more convenient. Anemometer Figure 9.2.3 The Wave Staff 180 readings were taken before and after wave pressure recording so that wind speed could be calculated for during the recording period as well as for the 24 hours before recording. Wave heights were usually estimated immediately after wave pressure recording on each day. A summary of events over the recording period is given in Table 9.2.1. Wave conditions for the first part were generally very calm. After two recording sessions of gaining experience in using the equipment, reliable wave pressure traces began to emerge. However, at intervals throughout June, the response of transducers No. 2856 (MG7) and No. 2858 (MG9) became rather spikey and this was thought to be due to the ingress of water into the transducers. At first, No. 2856 showed this erratic response, but later recovered. In the second part of the month, No. 2858 became progressively more spikey and then went dead for the final day of recording. Two days before the end of the recording period, No. 1937 (MG6) developed a break in the seal between the cable and the transducer, and seawater leaked into the body of the transducer. The result was a high frequency resonance producing a large amount of "noise" on the output signal. It was fortunate that these problems became acute only towards the end of the planned recording period. It was also fortunate that all four transducers were functioning perfectly over a period in the middle of the month when rougher wave conditions were experienced. It was in this period of rougher wave conditions that the wave staff came adrift from its anchor. The hawser on the anchor had been worn through, and the wave staff was found floating on the sea surface, still attached to the shore by the rope. A new anchor in the form of a reinforced concrete beam was found, and the role of the hawser was replaced by a stout chain. The wave staff was reinstalled six days after 181 Wed 30 May - Recording begins. Mild breeze from SW. Thur 31 May - Reliable traces. Fresh easterly wind. Wave heights small. Fri 1 Jun - Light southerly wind. Small waves. Transducer 2856 (MG7) has erratic trace. Sun 3 Jun - Transducers 1937 (MG6) and 2858 (MG9) also slightly erratic. Thur 7 Jun - Transducer 1937 (MG6) variable balance. Fresh, NE wind. Fri 8 Jun - Traces from all transducers improved. Sat 9 Jun - Light wind from west. Still very small swell. Sun 10 Jun - Swell wave height increasing. Transducer 2858 (MG9) becoming erratic. Fri 15 Jun - Fair wind from north. Reasonable swell. Sat 16 Jun - Wind shifts to westerly. Same swell. Wave staff detached. Mon 18 Jun - Same conditions. Silicon rubber ripped off exposed shore transducers. Tue 19 Jun - All transducers giving clear traces. Wind speed and wave height reduced. Thur 21 Jun - Light wind from south. Small waves. Wave staff reinstalled. Transducer 2858 (MG9) erratic again. Sat 23 Jun - Light breeze from south, but large swell from Atlantic. Sun 24 Jun - Decreased swell Mon 25 Jun -» Wind and swell increasing from SW. Rock scale in operation. Transducer 1937 (MG6) has break in cable and high frequency resonance Clarity of traces from other transducers poor, 2858 (MG9) particularly erratic. Tue 26 Jun - Very large swell. Transducer 2858 (MG9) dead. Wed 27 Jun - Recording ends. Table 9.2.1 Summary of Major Events at MG6 - MG9 in May / June 1979 182 it came adrift. At the end of the recording period, it was clear that rougher wave conditions needed to be recorded at MG6 - MG9. It was decided to return to the area later in the year after the transducers had been repaired. The wave staff was dismantled and the two ends of the rope were tied to a marker buoy so that the anchor could be reused. The hut was left in position, but the rest of the equipment was removed to a more secure location. On testing the instruments at Imperial College, all four of the transducers were found to be faulty. They were therefore returned to Kulite Sensors Ltd., for inspection and repair. Kulite Sensors confirmed that seawater had indeed seeped into the transducer bodies. In tracing the source of the fault, the waterproofing of the cable was checked by immersing a short section in seawater for one month. The resistance of the wires in the cable did not increase over this period indicating that the cable was watertight and that the water must have entered the transducers through the seals. Each transducer was dismantled and rebuilt using the original silicon semiconductors. New sealing com- pounds were used that were thought to be totally waterproof. The transducers were recalibrated and renumbered as shown in Table 9.2.2. below: Original Full Scale New Full Scale Transducer No. Output (mV) Transducer No. Output (mV) 1937 113.19 001 115.09 2857 79.63 2872 82.72 2856 81.47 2873 85.32 2858 88.74 2874 93.48 Table 9.2.2 Change in Transducer Calibrations after Repair It was noticed that the cable joint to the transducer was slightly proud of the flat underside which is bolted on to the backing plate. In order 183 to relieve any strain here, perspex discs were made to be inserted between the transducer and the backing plate for future recording periods. The complete recording system was reinstalled on MG6 - MG9 at the beginning of September 79. High winds prior to the first recording session produced a large swell on the St. Magnus Bay side of the minn that produced higher wave pressures than had previously been recorded. Unfortunately, however, one of the cable clips on MG9, which had been weakened during reinstallation, broke away from the shore. This allowed a length of cable to be pulled by the waves which subsequently lossened the backing plate. After the first day of recording, the transducer and backing plate on MG9 had become detached. Fortunately, it was quickly recovered and was not damaged. After the first day of recording, wave conditions became calmer and after two more days it was possible to reinstall the transducer and backing plate on MG9. In the meantime, good clear traces representing moderately rough conditions had been obtained from the other transducers. In the middle of September 79, the output from transducer no. 2874 (MG8) became very erratic. Seawater seepage into the transducer was suspected. Unlike the previous recording period, the erratic nature of the signal was not variable, but continued to deteriorate to such an extent as to make the trace unusable. At this time, wave conditions also began to become very rough again. By the evening of 18 Sept 79 the wind had increased to a very strong gale force from the west. On the next day, an extremely large swell was observed on the St. Magnus Bay side of the minn. The transducers on their backing plates had become detached from the shore at MG8 and MG9, and the rope from the shore to the wave staff had been broken. The rope must have been tangled around the anchor because the wave staff was still floating on the sea surface. Later recovery of the transducers from MG8 and MG9 indicated that they 184 had both been damaged by being thrown against the rock. The force collecting foil plate of transducer no. 2872 (MG9) had been punctured, and the cable had been pulled out of the transducer boty. Transducer no. 2874 (MG8) was in better condition but its output signal was still too erratic to be usable. Recording from the transducers on MG6 and MG7 continued for a few days before the whole system was packed up and removed from the area. Although many problems were encountered during the September 79 recording period, some very useful wave pressure traces had been obtained (Traces 31 to 42). Wave conditions were generally rougher than those in June 79 and seemed more representative of the long-term wave envir- onment of the area. With the exception of transducer no. 2874 (MG8), the transducers produced good, neat traces, showing that the new sealing compound was effective. It was clear, however, that a better method of attaching the backing plates to the shore was required. The climbing bolts were too easily dislodged in rough conditions. A new type of bolt which will be described in section 10.2 was used for subsequent recording periods. The two damaged transducers were taken to the manufacturers for inspection. They were confident that No. 2874 could be repaired whereas No. 2872, with its punctured diaphragm, was too damaged for repair. A replacement transducer (No. 3131; see Appendix 7) was purchased, whereas No. 2874 was renumbered as No. 2828 after it had been repaired. 9.3 Recording at MG2A - MG3A In order to measure wave pressures at the sheltered end of the range, the two undamaged transducers in September 79 were installed on sites adjacent to MG2 in Sullom Voe and MG3 in Culsetter Voe. The 185 positions of the two sites (MG2A and MG3A) depended mainly upon cable lengths from the proposed site for the recorder on the road at Mavis Grind. Since there was no suitable bedrock surface on the Culsetter Voe side within range, the transducer for MG3A had to be bolted on to a large boulder on a highly particulate section of shore. Although the physical characteristics of this shore were different from MG3, exposure grades for the two sites calculated from September 79 data were identical at Grade 7.75. Similarly, exposure grades for MG2 and MG2A were identical at Grade 7.00 (September 79 data). It must be appreciated, however, that for reasons already stated (section 5.1), this probably does not accurately reflect the wave exposure of this area which is likely to be more exposed. The recorder, signal conditioning module and battery were wired up on the back seat of a car. For recording sessions, the car was parked in the position shown in Figure 9.3.1, such that the cables from the transducers could be plugged into the signal conditioning module. The cable from transducer No. 001 (MG3A) was pulled across the road for each recording session. To avoid damage to the cable from passing vehicles, an alkathene water pipe covered the section that lay over the road. This was not totally effective since small spikes were observed whenever a heavy vehicle passed over the cable. The anemometer was installed close to the car position as shown in Figure 9.3.1. Wave height was estimated from fixed points at both sites using a ruler or cross-staff held vertically in the water. Recording at Mavis Grind began at the end of September 79 and continued until the end of October 79 (Traces 51 - 69). Over this period, the wind blew mainly from a south or south-easterly direction producing short period wind-driven waves at MG2A, and perfectly calm 186 Figure 9.3.1 Location of Wave Pressure Measuring Equipment at MG2A and MG3A 187 conditions at MG3A. In fact, simultaneous records for MG2A and MG3A were not obtained since waves were present at either MG2A or MG3A, but never at both sites at the same time. Winds from a westerly direction were only encountered on three days when very small wind driven waves were recorded at MG3A. Under these conditions, wind eddies would occasionally produce small ripples at MG2A, but these were not large enough to be recorded. Similarly, when the wind was from a northerly direction, small ripples were produced at MG3A, but again they were not large enough to record. It seemed that with wind blowing over the sector 220 - 340 , waves would be produced at MG3A, but if the wind blew from any other direction, waves would be produced at MG2A, with nothing but the occasional ripple at MG3A. Throughout the recording period, all the equipment operated sat- isfactorily. Because of the small waves being recorded, the amplifiers were usually set at full gain, and this was sufficient to measure the hydrostatic pressure caused by waves as small as 2 cm. in height. Incidently, raindrops landing on the transducers would also be recorded at this gain. The recording of such small waves meant that for representative recording, good timing was essential. With for example, a rising tide, there was often only a few minutes in which the waves were acting upon the trans- ducers before they were complete submerged. This period was of course shorter at spring tides than at neap tides. A large range of wave heights were observed at MG2A, and it was thought likely that representative conditions had been sampled at this site. Although only three days of records had been obtained from MG3A, much had been learnt about the wave exposure status of this site. The wind was blowing strongly from the west on the final recording day but only 3 cm waves were observed at the site. It was thought that waves in excess 188 of this size would rarely be encountered due to shallow water offshore allowing a large area of Ascophyllum nodosum to damp down any incoming waves. CHAPTER 10 The Wave Pressure Records Described 10.1 The Magnitude of Wave Pressures Recorded A typical set of wave pressure traces from MG6 - MG9 is from Trace 18 as shown in Figure 10.1.1. These were taken from a rising tide on Sunday 17th June 79 after the wind had been blowing steadily from the southwest over the previous two days. The mean wind speed over the 24 hours prior to recording was 15.79 mph (25.41 kph) while wind speed during the recording period was 19.20 mph (30.90 kph). The dominant wave height on the Atlantic side of the headland was estimated to be 1.00 m. and the Atlantic swell was penetrating through the minn in the form of secondary waves with an estimated height of 0.25 m on the sheltered side of the headland. It can be seen from the scales on the traces that the wave pressures were very low and could almost be totally accounted for by the hydrostatic head of water above the trans- ducers as the waves passed over them. Dynamic pressures from the waves appeared to be very slight and probably explain only small short duration irregularities in the wave form, particularly on the rising limb of the wave. On the time scale shown in Fig. 10.1.1, shock pressures are represented by a vertical spike on the wave form. In this section of trace, only one or two spikes are visible, and these are also of low magnitude. The trace from MG7 shows a small shock pressure on the rising limb of one of the waves, but the trace from MG8 shows that shock pressures may also occur after the wave impact. These shock pressures appear to be negative almost at the same instant as they are positive, and this is a typical phenomenon which will be discussed later. For much of the recording period at MG6-MG9, wave conditions were calmer than those described above. Overall wave pressures were also Trace 18. Sunday 17 June 79. Wind Speed during recording s 19.20 aph. Atlantic Wave Heights 1.00 m. to.I PSI AAAA^/UVAyvjwvyv rapor Speed i 5 mm/o 10 seconds vo Fimre >10.1.1 Trace of Section of Trace 18 O 191 lower, presumably because of smaller static pressures from smaller waves. Waves from these low swell conditions rise and fall against the shore in a confused mass of swirling water and foam. They would rarely fold over and break against the shore in a regular manner. However, on a few days conditions were such that a very large swell of up to 3.50 m. in height would come in from the Atlantic Ocean. Occasionally waves of this size would roll over and crash against the shore in the classic way as described in many textbooks. Under these conditions, the dynamic component of the wave impulse was increased as shown by the erratic form of the trace, particularly on the rising limb of the wave. The number of shock pressures and their magnitudes were also increased, particularly at the beginning of the wave impulse. A section of trace illustrating these features is shown in Plate 10.1.1, taken from Trace 31 on 11th September 79 when the estimated wave height on the Atlantic side of the headland was 3.00 m, and on the Culsetter Voe side of the headland, 0.55 m. The maximum shock pressure obtained from the work in Shetland was 4.55 PSI from the transducer on MG9 on 12th March 1980 when the estimated wave height on the exposed side of the headland was 3.20 m. (Figure 10.1.2). From the section of Trace 18 (Figure 10.1.1) or Trace 31 (Plate 10.1.1), it is possible to see the progression of a particular wave from MG9 to MG8. Once the wave passes through the minn, secondary waves develop so that the individual source wave cannot be identified' at MG7 or MG6. Indeed the mean wave period for the sites on the sheltered side of the headland is approximately half that for the sites on the exposed side of the headland. The mean wave periods for Trace 18 were as follows:- MG9: 4.011 sees; MG8: 3.957 sees; MG7: 2.959 sees; MG6: 2.741 sees. 192 MAVIS GRIM.,, SHETLAND. TIIACJ 31 11 SEP 79 Wint- Speed 28.CO rcpli direction 2C0' St. Magnus Day ave Height 3.00 ra. Culsetter Voe ,/ave Height 0.55 Paper Gpeed 5 ir.ni/s 0. GO Plat© 10.1.1 Section of Trace 31 10 seconds 4.55 PSI Figure 10.1.2 Trace of Section of Trace 78 193 The swell from the Atlantic ocean is most definitely the dominant influence on the wave climate in the area, with some amount of swell always progressing round the headland from MG9 to MG6. However, on days with a strong easterly wind, small wind driven waves develop in Culsetter Voe and are detected at sites MG7 and MG6 in the form of smaller waves superimposed on the swell wave. When these wind driven waves become larger than about 5 cm., small shock pressures become more frequent as the waves slap onto the transducers. Again, the magnitude of the shock pressure is very small, being generally of the same order of magnitude as the hydrostatic head of water in the wave. Waves at MG2A and MG3A are more simple because there is never any swell at these sites. They only develop when the wind is in a suitable direction, and they are characteristically steep with a short wave period of about 1 second. Over most of the recording period at MG2A - MG3A, the wind was blowing strongly from a south easterly direction over a fetch of one or two kilometres, producing waves as high as 0.40 m. A section of Trade 57 is shown photographed in Plate 10.1.2. The mean wind speed was 20.24 mph (48.67 kph) and wave height was estimated at 0.35 m. The mean wave period was 1.399 sees. It can be seen that shock pressures feature prominently on the trace, and are often up to twice the magnitude of the rest of the wave impulse which appears to be due to the hydrostatic head of water in the wave. Shock pressures are more common with wind-driven waves because they readily curl over and slap down onto the shore. The maximum shock pressure obtained from this site 0.760 PSI from a dominant wave height of 0.22m and a mean wind speed of 26.24 mph over the recording period. Shock pressures of this magnitude were never obtained at MG8 and MG9 where the wave heights were much larger. 194 5 OCT 79 iIG 2A MAVIS GRIND, SHETLAND. TRACE 57 C Y/ind Speed 30.24 mph direction 120 Paper Speed 5 mm/s Sullom Voe Wave Height 0.35 m. PSI 1.20 1.05 0.90 0.75 Plate 10.1.2 Section of Trace 57 - MG2A 0.1 PSI /VAAAAatWIAAaaaaa 10 seconds t i Figure 10.1.3 Trace of Section of Trace 67- MG3A 195 Wave heights no larger than a few centimetres were produced at MG3A even when the wind was blowing strongly from the west. This was due to the small available fetch and the occurence of large Asoophyllum nodosum plants having a damping effect on the waves offshore. With a mean wind speed as high as 21.68 mph (34.89 kph) during the recording period, only small ripples of 3 cm in height were observed at MG3A. These were re- corded on Trade 67, as illustrated in Figure 10.1.3. No shock pressures were observed, and it appears that the wave impulse was caused entirely by the hydrostatic head of water in the ripple. For the sites that were studied, it is clear that MG3A is at the sheltered end of the wave exposure spectrum, while MG8 and MG9 are at the exposed end. From biological evidence, MG6 and MG7 appear to be more exposed than MG2A, although greater shock pressures were encountered at the latter site when the wind was blowing with sufficient speed from the « optimum direction. The main physical difference between the two locations is that the influence of swell at MG6 and MG7 causes continuous wave action of low magnitude compared to the occasional wave action with greater shock pressures at MG2A. From studying other locations in Shetland, it seems that wherever the smallest amount of continuous swell penetrates, the shores are biologically more exposed than the sites open to local wind driven waves only. This indicates that continuous wave action is a more important influence on the littoral flora and fauna than the occasional maximum wave impact. In comparing the wave pressure records from sites dominated by wind-driven waves with those from sites dominated by swell, it is clear that the wave environment must be con- sidered over a suitable period of time. Methods of more precise com- parison are considered in the next chapter. A notable feature of the wave pressure measurements from all the sites was the low magnitude of the impact pressures that were recorded. In most cases, the main impulse from the wave could be attributed almost entirely to the pressure caused by the hydrostatic weight of water in the wave. Dynamic pressures were minimal, and any shock pressures that occurred were rarely much greater than the hydrostatic pressure. This supports the hypothesis that wave action influences the littoral flora and fauna mainly through water movement, for example caused by swell, rather than the actual wave impact. If this hypothesis is correct, it is still valid to use the wave pressure records as a measurement of wave exposure, since the water movement on the shore will be related to the various components of wave pressure measured by the instruments. a. 10.2 Variation in Wave Pressure at One Site. The routine measurement of wave pressures occurred with the transducers located on similar, flat, open surfaces of rock having slopes of about 30°. In order to see whether larger or different wave impact pressures would be recorded from different situations on the same site, all four transducers were mounted for a short time on MG9, and later on 0P70. MG9 was chosen because it was the most exposed site that had been recorded, and 0P70 was chosen because it was a site that appeared biologically similar to MG6 and MG7 in a different wave environment. 0P70 (South of Swarta Taing) is situated on Calback Ness facing Orka Voe at the southern end of Yell Sound. It is a site that is influenced both by swell and wind driven waves (Hydraulics Research Station, 1976) , although the latter are probably more important here than they were at MG6 and MG7. In addition to studying the variation in wave pressure at one site, it was thought that by recording wave pressures at OP70, the hypothesis concerning the relative biological importance of swell and local wind-driven waves could be developed. 19 7 The study at MG9 and 0P70 was carried out in March 1980, after it had become clear that a better method of attaching the transducers and cables to the shore was required. The new method of attachment involved using at least two "Rawbolts" (Figure 10.2.1) for each backing plate. These use the same principle as the "climbing bolt", although the gripping action against the sides of the bolt is maintained by the cone which is pulled through the middle of the expanding section by tightening the backing plate against the bolt. Unlike the "climbing bolt", it needed to have suitable holes drilled for it, using a conventional drill. A Skill percussion drill was used that was powered by a portable generator. Fortunately, this heavy equipment could be transported to MG9 by boat and to 0P70 by landrover. For attaching the cables to the shore, special cable clips (Figure 10.2.1) were made so that up to four hose pipes (containing, cable) could be clamped between two sections of aluminium alloy channel. The clips were then attached to the shore using two "Rawbolts". The layout of the transducers on MG9 is illustrated in Figure 10.2.2. One transducer (VER) was mounted on a vertical surface at the back of a rock step on the same tidal level and within one metre of the normal position for the transducer (NOR) at this site. Another transducer (FLA) was mounted on a horizontal surface of rock on the other side of the normal position, but also within one metre of the transducer coded NOR. These three transducers were all on a slab of rock facing the wave approach from the Atlantic Ocean. The final transducer (GUL) was located in the bottom of a shallow gulley near to the transducer coded FLA, but sheltered from the dominant wave approach. Over the recording period from 5 March 1980 to 14 March 1980, (Traces 71 - 80) wave conditions were generally rougher than normal at MG9. On the roughest day, the dominant wave height offshore was estimated 198 a A Rawbolt U Cable Clip (Slevation) 11SS11 r i3i I Cable Clip (Side Cross-section) Rawbolt Figure 10.2.1 Details of Rawbolt and Cable Clip 199 3 m. 3 m. c=» Cable clips ** Transducers Plan of Lower Shore Area of MG9 Figure 10.2.2 Positions of Transducers and Cable Clips on MG9 200 to be 3.20 m, and clear traces (Trace 78) were obtained from all the transducers. A typical wave form from each transducer was plotted on to microfilm from a digitized record of the trace. The technique will be described more fully in the next chapter, although a print from the microfilm is shown here (Figure 10.2.3) produced by program FORCE 3A (Fiche 1)). It was characteristic that most of the shock pressures, and indeed the largest shock pressures, were recorded from the transducer mounted vertically (VER) . This was to be expected since each wave would have a high chance of enclosing a pocket of air as it crashed against the back of the rock step. The confining nature of the rock step would also favour shock pressures since there could be little shedding of the wave impact away from its vertical rock surface. The typical wave form from the normally mounted transducer is similar to the one from the transducer coded VER, but the shock pressure component is not shown because it occured less frequently. The in- fluence of the dynamic pressure of the wave against the transducer is suggested by the rapid fluctuations in wave pressure on the rising limb of this trace. The actual contribution of the dynamic pressure to the total wave impulse is perhaps shown by comparing the typical trace from the normally mounted transducer (NOR) with the trace from the horizontally mounted transducer (FLA) . The wave would typically pass across the latter transducer without actually impacting on it. In this case, most of the wave impulse would presumably be caused by the hydrostatic pressure of water above the transducer. A suction effect as the wave pulls away from the normally mounted and horizontally mounted transducers can be seen at the end of the wave pressure impulse. The effect of turbulence as the wave passes over the horizontal trans- ducer can also be seen at the beginning of the wave form. The suction effect is particularly noticeable at the beginning of the wave form from the transducer mounted in the gulley (GUL) . A typical wave here r- >r Or e oi-j 0«-| OS-I 02-1 os-o 09-0 OS'O OO'tf" (ISd I 3»nSS3Md JA«M CE _J LL. oo r- X If I 0I"» MM OVO 0»-0 3S-0 Cof ItSd: 3»nSS3l»«i jAHl Figure 10.2.3 Typical War© Forma from Four Transducers Mounted on MG9 - Trace 78 Zot 202 would push up from under the transducer. Most of the rest of the wave form would be due to the head of water above the transducer. An exception to this often occured when the wave would fall onto the transducer after passing across the first slab of rock and into the gulley. The transducers were mounted in similar positions on 0P70, although the topography of the shore was somewhat different to that at MG9. It consisted of small sandy beaches alternating with flat outcrops of rock backed by 10 m. high cliffs of loose material and peat. (Figure 10.2.4). The topshore of 0P7O was steep and separated from the flat lower shore by a deep gtilley. One transducer (GUL) was located about 20 cm. down the landward facing vertical wall of the gulley in a very sheltered position. The other three transducers were mounted at the same tidal level, but on the seaward side of the flat lower shore slab of rock. These transducers faced the dominant wave approach and were mounted at angles of 0° (FLA), 20° (NOR), and 70° (VER). The recording in- struments were housed in a landrover at the top of the cliff, and recording took place from 16 March 1980 to 27 March 1980 (Traces 81 - 92). A section of Trace 82 is illustrated in Plate 10.2.1. Over much of the recording period, the wind was blowing strongly from the south east, producing local wind driven waves up to 0.37 m. in height. Shock pressures featured prominently on the records from the seaward facing transducers, but the transducer in the gulley (GUL) merely recorded the pressure caused by the rise and fall of the waves. For a short period, the wind was blowing from the north, and refracted waves from Yell Sound produced a small amplitude of up to 0.45 m. Fewer shock pressures occurred with these waves. From Hydraulics Research Station (1976) predictions, it seems that waves of up to 1.00 m. in height may be expected in Orka Voe with greater wind speeds from this PLAN OF 0P7Q NOR 20° Figure 10.2.4 Location of 0P70 and Positions of Transducers and Cable Clips 204 CALDACi: NiiSS, SII3TLAX1*. TitACE 81 17 i.'AH 80 Orka Voe .avo lici'tlit 0.22 r.. l'a:ier Speed 25 nni/s I Plate 10.2.1 A Section of Trace 82 - 0P70 205 direction. They also state that a continuous groundswell of a few centimetres may be expected in the voe. Typical wave forms (Trace 91) from the three seaward facing transducers during a strong south easterly wind are given in Figure 10.2.5 (produced by program FORCE 3A (Fiche 1)). With these locally produced wind-driven waves, similar but more exaggerated features to those recorded at MG9 may be recognised. Shock pressures are much more common and of greater magnitude on the vertical rock surface (VER), although the rest of the wave impulse is similar to the normally mounted transducer (NOR). The trace from the transducer mounted flat (FLA) 'is of smaller magnitude but the passage of water across its diaphragm causes much turbulence, sufficient even to cause the occasional shock pressure due to air entrapment. The trace from gulley (GUL) is not illustrated because it was not possible to identify particular waves which had first impacted against the other side of the rock slab. The general form of the trace from the gulley was of smooth oscillations related to the rise and fall of the waves, with no shock pressures. Although wave impacts did not occur in the gulley, its flora and fauna was similar to other locations on the same transect. This supports the hypothesis that perhaps water movement is a more important influence on littoral ecology than actual wave impact pressures. It must be pointed out that the wave forms shown in Figures 10.2.3 and 10.2.5 were selected as being typical. Frequently the wave patterns were different, and for example, shock pressures were at different times recorded from all the transducers. However, at all times the overall magnitude of the wave impulse was similar at the various locations. This is presumably due to the large component of wave pressure provided by the static weight of water in the wave. The dynamic and shock pressure components merely produce variations in this overall wave form. Figure 10.2.5 Typical Wave Forms from Three Transducers Mounted on 0P70 - Trace 91 lO 6 207 10.3 Shock Pressures Shock pressures occurred infrequently in the wave pressure traces with the transducers located in any position. At recording paper speeds of up to 25 mm/s, they appeared as vertical spikes in the trace that sometimes became negative at almost the same instant that they were positive. They were most common with local wind-driven waves, when the waves would curl over and slap on to the shore. In this case, they would usually occur at the beginning of the wave form, and would be up to twice the magnitude of the rest of the wave impulse. The actual magnitude of the shock pressures was not predictable, but they were never very large in comparison to previously recorded shock pressures, (for example by de Rouville et al., 1938). The maximum shock pressure recorded from Shetland was 4.55 PSI, from a swell of 3.20 m. on MG9. On records from these larger swell waves, shock pressures would often occur through- out the wave impulse due presumably to their very turbulent nature. Shock pressures occurred most frequently from transducers mounted on vertical surfaces of rock. Shock pressures are formed by an air pocket becoming entrapped against the shore as the wave hits it (Bagnold, 1939). Optimum conditions for their formation are rarely achieved, since the size of the air pocket and the configuration of the receiving structure are of critical import- ance. This explains why the magnitude of shock pressures cannot be predicted from wave height alone. It was consequently very difficult to decide when to record for shock pressures at fast paper speeds, since the paper could never be run at very fast speeds for more than a few seconds at a time. However, very good definition of a shock pressure was obtained with a paper speed of 1000 mm/s from Trace 82 when a strong south-easterly wind was producing waves estimated at 0.22 m. at 0P70. Plate 10.3.1 shows parts of shock pressures from several transducers simultaneously. It can be seen that much of the shock pressure consists 208 Erratic- Plate 10.3,1 Shock Pressures from Trace 82 - 0P70 i of a rapid irregular fluctuation, part of which does indeed become negative. This phenonemum is confirmed by Kamel (1971) to be a real effect due to rapid compression and expansion of the air pocket. Also noticeable on the trace is a smaller amplitude regular oscillation. This is most likely due to resonance within the body of the transducer. The fact that shock pressures are events of such short duration makes them difficult to study. However, it is likely that they will provide the maximum wave pressure likely to be encountered on a particul site. By the nature of their formation, they must occur over a very small area, and as such their biological significance is far from clear. It has been shown that they are more likely to occur in certain location such as on vertical rock surfaces at the back of a rock step. Species requiring sheltered conditions are rarely present in these locations, but they are often to be found in small hollows where shock pressures might also be expected. The fact that they tend not to occur on the vertical rock surfaces may be due to problems of attachment for spores and larvae in areas of rapid water movement. 10.4 Instrument Testing The low magnitude of wave pressures encountered gave some cause for concern since much larger wave pressures were expected. A possible explanation for the low magnitude of shock pressures was that the transducers were unable to respond fast enough to a rapid impulse. The frequency response of the Soil Pressure Cell was not specified, although it was estimated to be fairly high. To test this, the output from a Soil Pressure Cell was compared to that from a transducer with an inherently faster response in a test rig (Figure 10.4.1). The reference transducer was supplied by Kulite Sensors Ltd., and was in the form of a small flush diaphragm (diameter 5 mm.) threaded 2lO Perspex Piston o.SS<«- Water Perspex Cylinder Brass Chart Block r Amplifiers Recorder Cables from Transducers Sketch Diagram of Test Rig Reference Soil Transducer Pressure Cell I Reference mm Transducer Bolt Brass Block Soil Pressure Cell Section through Brass Block Plan of Top of Block Figure 10.4.1 Transducer Testing Rig 211 cylinder - Kulite Model No. XTM-1-190-50G. The sensing element was directly behind the diaphragm, giving the instrument the capability of responding to frequencies of at least several KHz. The reference transducer was mounted next to the Soil Pressure Cell in a brass block such that both diaphragms were flush with its top surface. A perspex cylinder was secured to the top "of the block, and this was filled with water so that it could be vibrated with a loosely fitting piston. The vibrator was actuated by a Muirhead D-880-A oscillator. The same input (10 V) was supplied to both transducers, and their output was adjusted through the signal conditioning module such that each transducer gave a deflection representing 0.3 PSI per centimetre on the chart recorder. The water column above the transducers was vibrated at frequencies ranging from 1 Hz to 2000 Hz, the upper limit for the writing capability of the chart recorder. The output from the transducers was recorded at paper speeds up to 1000 mm/s, depending on the definition required. At all frequencies and paper speeds, the output from the two transducers appeared to be the same. At higher frequencies, there was/no loss of amplitude from the Soil Pressure Cell as might have been expected if the frequency response was suspect. At 2000 Hz and 1000 mm/s paper speed, every cycle from both transducers could be detected from the trace, although the trace was very faint. At low frequencies (1 - 10 Hz), the piston would travel jerkily up and down the cylinder causing spikes on the trace similar to those produced by natural waves. In all cases, the response of the two trans- ducers was the same, although the peaks from the Soil Pressure Cell were perhaps more rounded. Over the complete frequency range, no resonance was detected from either transducer, thereby indicating that the natural resonance frequency of the instruments was in excess of 2 KHz. 212 The overall conclusion was that the Soil Pressure Cell performed satisfactorily and could accurately respond to frequencies of up to at least 2 KHz. Removing the silicon rubber from the Soil Pressure Cell had no effect on the output. The cup anemometer that was used for recording wind speeds was of a large, robust design whereby the turning of the cups mechanically moved a guage registering in miles. It was thought that at low wind speeds, the inertia of the various components may cause an underestimate of actual wind speed. In order to test the accuracy of the anemometer, it was inserted into a 3 X 3 ft. wind tunnel (Figure 10.4.2). Actual wind speed in the tunnel was measured with a Betz guage. This is a water-filled manometer which is acted on by air pressure in the wind tunnel. Height of water in the manometer may be converted to wind speed by: , 2 Bernoullis Equation* uI. —= pr •»>• 3i rt> vv r>jc — ulcooulc o s ^ a Total Static Dynamic P = density of air 2 a P - P = | P V P = density of wate o s * a w Barometer Equation: P-P=Pgh V = velocity ° 2 S Thus: | P V = P gh g = acceleration a w due to gravity 2P gh V = — h = height of water T a column. V = 13.13 h ft./sec. or V = 8.95 h m.p.h. Wind speed in the tunnel was increased in stages (with a turbulence grid in position) to a maximum of about 40 mph (65 kph) . At each wind speed level, five minutes was allowed for the anemometer to reach the speed, and then wind speed was recorded over a further five minutes. Readings were also taken while the speed in the tunnel was reduced. A low and a high speed were then recorded without the turbulence grid 213 I Bet 2 Guage 0.6 m t PT I f-Po Cup Anemometer 0.9 m o (3 ft) a o f 0.3 m 1 i Figure 10.4.2 Sketch of Long Section of Wind Tunnel 214 • Turbulent air O "Smooth" air Anemometer m.p.h. 52 \ / % // // / Ll i 16 24 32 40 48 52 m.p.h, Beta Guage ("Real") Figure 10.4.3 Wind Speed Recorded by Cup Anemometer vs. "Real" Wind Speed Measured by Betz Guage 215 in position. The relationship between "real" wind speed as measured by the Betz guage and the wind speed recorded on the anemometer is given in Figure 10.4.3. As predicted, the cup anemometer underestimated low wind speeds, and appeared to be rather innaccurate with a "real" wind speed of less than 12 mph (20 kph) . The lowest wind speed that would turn the cups was about 7 mph (11 kph). In Shetland, or in the field, lower wind speeds would probably turn the cups due to gusts being able to come from different directions. The wind tunnel could obviously not approximate field conditions, and it is likely that the true performance of the anemometer at low wind speeds is closer to the anemometer = real line in Figure 10.4.3. 216 CHAPTER 11. Processing the Wave Pressure Records 11.1 Digitising and Data Reduction For a precise comparison of wave pressures between sites, it was necessary to extract certain statistics from the traces. Since this could most easily be done with the aid of a computer, the first stage of the data reduction process was to digitise sections of each trace into a series of coordinates in terms of time (seconds) and wave pressure (PSI). From the digitised traces, the following statistics were extracted: Maximum wave pressure Significant wave pressures at 33%, 10%, 1% of peaks Integrated wave pressure 50% exceedence wave pressure Wave period A Cetec digitiser connected to a Texas time-sharing terminal was used to input coordinates to a series of files in the computer that were labelled RAWIN. The digitiser consisted of a hand-held cursor with siting cross-wires and a button that was laid on top of the trace which was on a special board. Each time the button was pressed a pair of coordinates in relation to the dimensions of the board were sent to the terminal. The most representative portion of each trace was selected. This was taken as a period immediately before (on a rising tide) or immediately after (on a falling tide) the transducers were completely submerged between waves. A 5 mm/s section of trace was usually chosen, although enough detail was sometimes present on a 1 mm/s section for MG8 and MG9. The trace was digitised at points where there was a rapid change in wave pressure. Sampling in a less subjective manner was considered, but ruled out since it was thought that regular or random sampling would be unlikely to adequately represent shock pressures. About 300 seconds of each trace were digitised, although for a 5 mm/s trace, 217 the width of the Cetec board would only allow the input of about 100 seconds at a time. Thus the headings within the file called RAWIN for Trace 18, for example, would be: T18AMG6, T18BMG6, T18CMG6, T18AMG7, T18BMG7 etc. Under each heading, the first three pairs of coordinates were the reference points on the board relating to the origin, the end of the X axis, and the end of the Y axis. These were necessary for the trans- formation of the following coordinates into figures in terms of seconds and PSI. Trace numbers 3-69 were digitised in this way. Traces 1 and 2 were too incomplete for data processing. The transformation of the data file RAWIN, was carried out by program WAVES (Fiche 1) that was usually run from the terminal. Program WAVES calls upon library sub- routines CETEC, FACTORS and TRANSFM which have been written by A. Ludlow, Imperial College, for this type of application. The input to program WAVES was RAWIN, together with the values of the reference coordinates in terms of seconds and PSI provided from the terminal. The output from the program was a series of files called RAWOUT which consisted of the headings followed immediately by the transformed data. Storage of the digitised traces was on magnetic tape using the system known as UPDATE. Each line of the data is identified by the name from the heading and a number sequence. This allows sections of the file to be easily handled using special UPDATE directives. By preceeding each heading with * DECK in the initial digitising process, the heading was automatically removed and used as the identifier in the UPDATE system. This then allowed for the insertion of headings at only the most appropriate places. For example, the sequence of headings for Trace 18 was: T18,MG6; T18,MG7; T18,MG8; and T18,MG9. Once the data was in the UPDATE system, files could easily be merged for the occasional addition of digitised traces to the magnetic tape. The complete contents 218 of the magnetic tape containing digitised traces without identifiers are given in Fiche 4. A small section is printed as Table 11.1.1. The form of the digitised traces may be seen in Figures 11.1.1 to 11.1.6 in which the first 72 seconds of digitised traces from Trace 31, Trace 57, and Trace 67 are displayed as prints from microfilm plots (program FORCE 3B (Fiche 1)). They give a representative trace from each of the sites at which wave pressure measurements were taken at Mavis Grind. The similarity between digitised and actual trace may be observed in some places where the actual traces have been drawn on to the figures. The main difference between the actual and digitised trace is that the latter is more angular. In addition, shock pressures are also not often well represented by the digitised trace. Shock pressures were extracted from the digitised traces by a process which will be described later. Program FORCE (Fiche 1) was written to extract and compute various statistics from each wave pressure trace. In subroutine SIG, the wave pressure peaks were identified and stored as an array so that the max- imum wave pressure could be extracted and the significant wave pressures could be calculated. The significant wave pressure (SIG) was calculated as the mean of the highest one-third of the peaks in the trace. This is exactly analogous to the calculation of significant wave height (Tann, 1976). In a similar way, the significant wave pressure was also calculated as the mean of 10% -of the peaks (SIG10) and the mean of 1% of the peaks (SIG1). This latter figure was often the same as the maximum wave pressure. In subroutine TOTAL, the frequency of digitised wave pressures other than zero was expressed as percentage exceedence over twenty intervals throughout the range of wave pressures encountered. The percentage exceedence curve was plotted (subroutine GRAPH) and the wave pressure for 50% exceedence (P50) was extracted. The integrated wave pressure (INT) was calculated by summing the areas under each of 219 SECS PSI SECS PSI SEGS PSI SECS PSI 293.32 .00 295.81 .35 296.27 .34 297.57 .00 300.61 . 00 301.73 .25 302.82 . 00 306.20 .00 306.62 .20 308.58 .29 309.45 .00 310.89 .00 312.00 .24 313.13 . 05 313.41 .10 313.84 .00 314.23 . 06 314.62 .00 316.84 . 00 317.26 .06 317.64 . 03 318.50 . 14 318.82 .10 319.16 .15 320. 05 . 02 320.68 . 12 321.55 .05 323.40 .35 325.48 . 00 326.08 . 00 327.25 . 16 328.45 .20 329.34 . 00 331.81 . 00 331.80 .13 331.93 .05 333.62 .29 334.95 . 00 336.88 .00 338.58 .45 339.60 . 00 340.02 . 00 340.24 .06 340.88 .00 341.93 . 00 342.26 . 07 342.64 .04 343.44 .21 343.92 .20 344.33 .11 345.65 . 00 347.80 .00 349.14 .35 350.44 . 00 350.59 .24 350.66 .04 350.80 . 06 351.16 . 02 351.56 .08 352.22 .00 354.13 .32 354.50 .28 355.08 .33 356.25 .00 356.59 .00 356.93 . 06 357.49 .00 353.85 .00 359.11 . 04 359.28 .00 359.76 . 00 361.61 .35 363.26 .00 363.52 .01 363-72: .05 364.06 .01 366.77 • . 00 366.81 . 09- 367.31 .05 368.01 .14 368.57 .07 369. 27" .10 369.57 .07 370.15 .19 370.47 .14 370.85 .21 371.31 .14 373.25 .24 374.42 . 00 378.61 . 00 379.14 .18 380.78 .36 382.48 . 00 383.40 . 00 383.72 . 04 333.98 .00 T31*MG7 .88 . 00 1.88 .11 2.50 .05 3.43 .41 5.00 . 00 5.88 . 00 6.20 .10 6.96 .00 . 8.93 . 00 9.39 .22 10.57 .00 11.16 .00 11.67 .11 12.22 . 08 12.89 .13 13.62 .01 13.93 . 07 14.40 . 00 15. 17 .10 15. 67 .00 ' 17.90 . 00 18.17 .31 18.71 .35 20. 04 .04 20.66 .11 21. 05 . 00 21.77 .00 21. 76 .16 21.86 . 04 22.44 . 16 23.09 .00 28.75 .00 29.48 .15 30. 19 . 00 31.42 .00 31.76 .19 32.54 .00 32.83 . 06 33.30 .00 34.79 .00 34.89 .38 34-. 89 .30 35. 04 .35 35. 67 .29 36. 00 .06 36. 91 . 13 37.96 .00 40.41 .00 41.22 .23 42.39 . 09- 43. 05 .14 44. 18 .00 45.38 . 19 46.61 . 00 48.79 .00 49. 25 .23 50-30 .00 51.70 .00 51.93 .05 52.20 .00 54. 05 .00 54.61 . 12 56.06 . 00 57.38 .00 58.11 .25 58.98 . 00 61.75 .00 62.06 .27 62.55 .33 64. 06 . 09 64.80 .20 66.19 .00 68.71 .00 69.40 .18 70.68^ . 02 71.46 .13 72.18 .04 73.30 . 34 75.86 .00 77. 12 .00 77.67 . 15 78.44 .00 79.91 .00 80.33 .22 81.65 .00 82.34 .00 83. 09- .14 83.68 .09 84. 08 .13 84.88 . 00 85. 67 .00 86.27 .21 87.89 . 00 88.35 .06 88.81 .03 89. 47 .25 90.28 .00 . _ 90-98 . .00 , 91.65 .19- 92.35 .10 Table 11.1.1 Print from Magnetic Tape Storage of Section of Trace 31 I·1J' 6 ...."-l ~ tot ~ ~ •~ •~ ~ > Ol CD n ....~ 0 ::s 0 a "" a \:! t:1 ,Jl, 0 .... 9J .oo gq...... ,.~ m CD ~ t-i tot pa n CD tot ""0 a !§ 0\ t-i s-tot n CD w ~ r • i T31 MG7 I ....~ .I ~ '1 ca a ID ..... •..... • J N ~"'(./).:. a... lJ.J en O:::a ca ::JCI> 0 l/).,; l/) ~ UJ .... 0::: 0 a... :s 0 ~ ~ ....'=' ~ OQ...... ~ CD p. ~ '1 SD n ca Me a '1 ID 0 El liC: c;) ~ ~ '1 SD 0 ca w ...... ( ' / "· ./ ~I ~ - - . ..- '---,----LT- - --,----.,..- - --r-..._..·- - -, ,_./-, ~6 .oo 3 ~ .oo ~. 56 .oc St!. J J 60.00 62.00 64. 00 6 6.00 68 . 00 7Q . ~ ;;, '/'l . 0•.1 f -· - - ---· ------[ . T31 MG8 r 0 U) - a::o~ :J \ 22 .oo . z• .oo 26 .oo 26 .oo 30 .oo 32 .oo 3• .oo 36 .oo •. 0 U) , , • 1 / ' . ·,. A I \ I ( \ ,. \ I I ·. '! .o 4 .oo _ _ "=,.~~- --;~-..-----.---,- ....::::,..__ r- _ 56 .oo 5tl. oo ss . .;o ~ ·70 . 0 l 1 11E • SEC S t 6o.o s2.oo s'coo s's.oo -} . QQ T31 9MG9 I~ I l w Q:: o i ::J OO I (/)~ (/) w I. 0:: (L ! 0 0 ~·~.-o-o--~.------.·.o-o-----,--~,------.-~- --.------.---~"Js-.-oo----JTB-.o-o~--2'o-.o-o ---.2 2-. -oo----.--~===r====~~-=~.------.--~-r.-~ TIME lSECSl Mv\ \ I I \ \ · ~ '* \ I~ I / . I \ I I I - · I I I I I II I .. , •uO .-: · . ~ ,) 52 .oo 54 .oo 56 .oo 58 .o o 6 0 .OG 62 .oo s• .oo 6 .oc ! ME ( SEr S I '.; .: T57 MG 2 .....~ ~ •"1 ~ .· •....~ • tl' en CD Q ~ 0 ..... UJ ... :s0 ~ ~ 0 N ..... ~ 3: g4-L----'---'r---'---'r--->--L-r--~ '---'r- - - ~), 6 (\ 1"'0, C\ !{\ 6 .I\ 6 /_ ·s.oo fl.oo !O- Do 12.ou !4.00 1s.oo 18-00 2o.oo 22.00 24. 00 2s.oo b28.oo (),3o.oo 32 .oo 34.00 t:1 2 .oo 4 .oo 4: TIME !SECSI oq...... c+ CD CD ~ ~ s-'1 n f· 0 •.... "' '1 s0 IC 0 N UJ > a::o :=J ill \1) ~ \1) t-3 UJ a:: . -~ '1 a... s- 0 Q UJ ... • a:>~ 3: U1 ~ ,- ~i/\ 6 !~: . J :_ • • . 1 ~s.oo 38 . o n .oo · ~ .o n 44. 0~ . ~ .. ...... .. T6 7- MG3 ...tal ~ '1 ca ~ ...... • -o .... -"'(/)..: •~ ~ UJ cro .· =>"'? til U"lo ca U') () w a:: ~ Q...... 0 0 w• ::s a:o>" ~ 0 Ma .... 0 C? ...... , c. ... / "-a OQ 14 . 00 1 6 . 00 1~ • 00 2o.oo 2'.oo 24-0o zs.oo · · "e .oo 30.oo 34.00 T IME l SECS l 1~ - uo 3S.oo ~ ....c+ ...ca ca ~ ~ '1 SD () ca ~ '1 1 " 0 • I a !§ w > w a::o :JCD • U')~ ~ U1 UJ "1 a:: I» Q... () ca 0\ ~ - ,- -I ~ ..... ·' ~ - -,2 . ·a" ...., s'4 ;-~u--~5 s~.o r,-~ ----cr=~-.-.u-tl=:::...... -b~f: .:."'"o o-c:::,..E.... ~ -..::.;;:.:o-... ::-...:::::G::;;· ·:· ~~ . - - "'";; ~ ofo'~to , ·- · l t. ~a I "1 £" I ~ E CS; ---'-"-"--- ·- ~ ------226 the waves in the trace. Area was calculated using Simpson's Rule in the form of: Area = E[(Y + Y ,, ) (X .--X )/2l where Y = PSI and X = L n n+1 n+1 n 1 seconds. The integrated wave pressure was expressed as the total area under the curve per minute of trace. Finally, the mean wave period (T) between peaks was calculated. Before the digitised wave trace data were transferred to magnetic tape, it was copied without identifiers to a file called TRACE. This was used as the input to program FORCE. A typical output from the program was obtained from'Trace 31, which is displayed in Fiche 5. For each site, the total number of data points and the position and magnitude of peaks in the trace were given. Then followed a listing of the ten highest peaks in the trace, the mean wave period between peaks, and the significant wave pressures. The numbers of peaks used in the computation of these figures were also given. The integrated wave pressure value was then followed by the percentage exceedence graph and the coordinates of points on the graph. Finally, the total number of points with wave pressure not equal to zero was given, together with the length of the digitised trace in seconds. As more traces were digitised and processed in this way, certain patterns began to emerge. For example, the percentage exceedence curve was roughly linear until higher wave pressures were reached when it would flatten out. Sometimes the linear portion would be more like a hyperbola, or sometimes the whole curve would be slightly sigmoidal. For the more exposed sites, a large number of points were sometimes digitised slightly below the baseline representing the negative pressure of the backwash of the waves. On the percentage ex- ceedence curve, this would produce a large drop in percentage exceedence near the wave pressure = 0 line. This illustrates the fact that the form of the percentage exceedence curve depends upon the subjective selection of points on the trace to be digitised, and demonstrates that integrating statistics should be viewed with caution. Nevertheless, a useful statistic to extract from the curve appeared to be the wave pressure value that was exceeded at a frequency of 50% (P50). This, together with other useful statistics, was written to a file called RIPPLE, which is reproduced as Table 11.1.2. From RIPPLE, it can be seen that all the selected statistics appeared to vary together. For example, a high maximum pressure was reflected by high significant wave pressures and integrated wave pressures expressed as INT and P50. Indeed, the wave period (T) was also usually greater with a higher wave pressure. Because of the subjective sampling procedure in the digitising of the traces, more confidence was placed in maximum and significant wave pressure values. Since maximum wave pressures were usually provided by infrequent shock pressures, the most reliable estimates of wave exposure were thought to be provided by the significant wave pressures. In order to investigate the frequency of occurrence of shock pressures on the digitised traces, subroutine SHOCK (Fiche 1) was written for use with FORCE. It was recognised that the digitising process only included the major shock pressures, and that often only one was digitised when many occurred together. Nevertheless, the position and magnitude of shock pressures were extracted from the digitised traces on magnetic tape. For the analysis, shock pressures were arbitrarily defined as those having a rising and falling limb over a duration of 0.2 second or less. As expected, very few shock pressures were found from traces from MG6 - MG9, and often no shock pressures were registered. Most shock pressures occurred under rough conditions, but even then;it was rare for more than about twenty shock pressures to be digitised. Shock 228 Columnss e.g. T03,MG6 - Trace Number MAX - Maximum Ware Pressure S1G - Significant Wave Pressure (33$ SIG10 - Significant Wave Pressure (1$) INT - Integrated Wave Pressure (area under cur/e) P50 - 50^ exceedence Wave Pressure T - Wave Period MftX SIS SIG10 INT P50 T T03 MG6 .23 . 099 . 132 1.456 .051 1. 153 T03 MG7 -20 .118 . 141 2.160 .061 1. 045 T03 MG8 .21 .167 .190 2.006 .082 4.268 T03 MG9 .37 .335 .370 7.219 .132 7.63 B T04 MG6 . 17 .044 .072 .278 .021 1.113 T04 MG 7 .22 .100 .129 1.318 .062 1.101 T04 MGS . 12 .090 .110 1.495 .050 3.628 T04 MG9 .21 .210 .210 4.696 .142 8.665 T05 MG6 . 13 .073 .087 1. 029 .040 1.301 T05 MG7 .13 .102 .116 1.710 .061 2.799 T05 MGS .53 .373 .439 6.753 . 144 3.065 T05 MG9 .46 .273 .355 3.054 .090 2.399 T06 MG6 .13 . 071 .099- .998 .040 2.106 T06 MG7 • 17 .091 .125 1.421 .041 2.074 T06 MG8 .44 .326 .393 3.250 .113 4.670 T06 MG9 .53 .362 .467 6.101 .064 3.832 TO 7 MG6 .11 .052 .072 . 986 .031 1. 076 TO 7 MG7 .14 . 067 .091 1.228 .031 1.813 T07 MGS .33 .234 .289 3.551 .112 4. 4&6 T07 MG9 .53 .388 .448 6.379 .114 . 7.271 T08 MG6 . 12 . 048 . 060 .892 . 031 1. 04-3 T03 MG7 . 06 . 038 . 048 1.1 09 . 020 1.751 T08 MGS .20 - 126 . 169 1.756 . 060 5.287 T08 MG9 .51 .304 .376 6.320 . 153 9.244 T09 MG6 . 07 . 048 . 061 .889 .030 2. 150 T09 MG7 .10 . 093 .100 1.752 .040 4.478 T09 MGS .39 .292 . 334 5.190 .122 3.682 T09 MG9 .52 .422 .478 7.393 .170 6. 157 T10 MG6 .13 .063 .093 .865 .031 2. 076 T10 MG7 .16 . 030 .106 1.508 . 040 1.892 T10 MGS .58 .417 .504 7.619 .146 3.870 tio MG9 .55 .383 .494 6. Oil .141 5.100 Til MG6 .07 . 047 . 057 .661 . 030 1.541 Til MG7 .09 .056 . 068 1. 008 .031 1. 003 T11 MGS .27 .177 .215 2.746 .082 3.794- Til MG9 . 45 .336 . 374 6.252 .173 4.535 1 TI2 MG6 .09 .060 .076 1.060 .031 1.824 T12 MG7 .11 . 072 . 085 1.459 041 2.259 1 T12 MGS . 2 7 .198 .234 3.274 .110 2.179 ; T12 MG9 .36 .280 .330 5.883 .113 3.907 \ TI3 MG6 .12 .071 .093 .866 .041 1.951. { TI3 MG7" .15 .091 .113 1.391 .051 2.406 1 T13 MG9 .89 .397 .525r 4.922 .161 3.237 T13 MG9 w 73T .471 .591 7.670 .205 3.534 TI4 MGfr . 09 .060 . 077 .680 .031 2. 064 TI4 MGZ .11 .078 . 096 1.210 .041 2.46& T14 MG8 .45 .271 .344 4.776 .142 2.859 T14 MG9 .64 . 556 .613 10.302 .296 7.52& i Table 11.1.2 Print from Permanent File RIPPLE 229 T15 MG6 .15 . 096 .125" 1.604 .041 3. 005 T15 MG7 . 14 . 080 .107 1.495 . 031 2. 435 T15 MG8 .61 .447 .521 5.622 . 151 4. 437 T15 MG9 .85 .703 .820 11.947 .351 6. 352 T16 MG 6 .22 . 140 . 190 2.213 . 062 1. 871 T16 M67 .25 .143 . 185 2.592 . 062 2. 128 T16 MG8 1.31 .781 .973 14.203 .330 4. 404 T16 MG9 1.30 1.100 1.243 18.979 .442 4. 961 T17 MG6 .30 .205 .258 3.439 .102 3. 007 117 MG7 .36 .229 . 277 3.666 .101 3. 651 117 MG8 .89 .680 .798 12.247 .314 3. 879 117 MG9 1.40 1.032 1.233 16.096 .441 5. 669 11Q MG6 .29 .207 .254 3.257 . 082 2. 741 119 MG7 .34 .206 .255 2.943 . 081 2. 959 118 MG8 1. 09 .857 .994 12.801 .348 3. 951 11Q MG9 1.52 1. 063 1.261 17.707 .271 4. Oil 119 MG6 .22 .129 . 159 1.633 .061 2. 636 119 MG7 . 19 . 141 . 175 2. 073 . 061 3. 196 119 MG8 .84 .678 .788 13.840 .318 4. 158 T19 MG9 1. 07 .732 .890 12.360 .325 4. 766 T20 MG6 .29 . 139 . 192 2. 175 . 061 3. 141 T20 NG7 .24 . 138 . 180 2.236 .062 3. 458 T20 MG8 .93 .618 .733 10. 007 .291 5. 271 120 MG9 1. 02 .752 .917 12.696 .402 6. 514 121 MG6 .15 . 071 . 097 .865 .041 1. 2 06 121 MG7 .11 . 068 . 085 1. 174 . 041 1. 104 121 MG8 .39 .305 .344 5. 347 .133 3. 749 121 MG9 .67 .551 .624 8.351 .282 7. 548 122 hG6 . 12 . 059 . 080 .895 . 031 1. 771 122 MG7 .10 . 060 . 082 1.284 . 030 2. 354 122 MG8 .55 .391 .473 5.907 . 180 5. 009 122 MG9 .72 .511 . 636 7.876 . 253" 7. 681 123 MG6 .23 .118 .169 1.728 .051 2. 005 123 MG7 .22 .152 . 192 2.565 .070 3. 421 123 MG8 .85 .652 .764 13.391 .337 4. 361 123 MG9 .99 .805 .953 15.139 .350 6. 045 124 MG6 .56 .424 .527 6.382 . 174 8. 568 124 MG7 .52 .343 .434 6.320 .125 6. 465 124 MG8 1.55 1. 089 1.346 18.835 .403 5. 783 124 MG9 1.75 1.250 1.512 19.159 .483 7. 356 T25 MG6 .12 . 060 .087 1.073 .031 1. 673 T25 MG7 .13 . 073 .099 1.270 . 031 2. 481 T25 MG8 .58 .406 .486 6.704 .244 5. 507 T25 MG9 .84 .642 .736 10.387 .412 8. 141 T26 MG6 . 17 .137 .160 1.806 . 082 6. 144 126 MG7 .18 .109 . 144 1.322 . 061 3. 313 126 MG8 .66 . 482 .583 6.486 .290 5. 532 126 MG9 1. 06 .772 .920 10.791 . 477 7. 543 127 MG6 .34 .256 .307 3.598 .091 3. 704 127 MG7 .39 .260 .332 3.878 .102 3. 708 127 MG8 1.59 .884 1. 056 14.427 .345 5. 497 127 MG9 2. 03 1.629 1.795 25.599 .571 6. 615 12Q MG6 . 15 .094 .118 1.229 . 051 1. 832 T28 MG7 .17 . 124 .151 1.874 .071 1. 903 T28 MG8 .76 .576 .664 10.415 .313 2. 917 T31 MG6 .49 . 322 .415 4.696 .113 3. 538 131 WG7 .50 .322 .408 4.396 . 135 3. 924 131 M68 1.78 1.218 1.403 .24.650 .604 5. 009 131 MG9 1.89 1.477 1.733 27.016 .550 4. 085 Table 11.1.2 (cont) Print from PermanentFil e RIPPLE 230 T32 MG6 ~ .44 .258 .334 51325 .114 3.396 1 T32 MG 7 .33 .226 .277 4. 004 .112 3.96 0 1 T32 MG8 .97 .727 .857 12.929 .297 5.940 . T33 MG6 .29 . 179 .233 3. 058 .093 2.595 T33 MG7 .41 .211 .270 3.445 .090 3.257 : T 33 MG8 .94 .623 .731 10.848 .354 4.757 : T 34 MG6 .13 .083 .106 1.073 .040 3.263 T34 M67 . 13 . 089 .105 1.493 . 040 3.305 T34 MG8 .68 .449 .557 9.413 .211 4. 174 T34 MG9 .87 .638 .770 10.785 .244 5.669 T35 MG6 . 17 .116 . 147 1.728 .061 3.84C T35 MG 7 . 19 . 125 . 155 1.950 .061 3.37* T35 MGS .70 .562 .640 9.879 .287 5. 06* T35 MG9 .67 .532 .600 9. 178 .277 5.79* T36 MG6 .23 . 173 .233 3.150 . 081 2.349 T36 MG7 .30 . 191 .234 3.132 .090 3.482 T36 MGS .95 .806 .895 16.338 .427 6.282 T36 MG9 1. 08 .806 .973 15.666 .410 5.593 T 37 MG6 .41 .221 .290 4. 077 .103 3.66* T37 MG7 .35 .233 .284 4.187 .122 3.987 T37 MG9 1. 02 .751 .908 15.550 .449 6.575 . T38 MG6 .36 .265 .309 4.207 .112 3. 194 T38 MG7 .43 .282 . 344 4.505 .142 3.752 T38 MG9 1.14 . 879- 1. 028 13.645 .410 6.42S T39 MG6 .67 .412 .582 4. 048 .194 5.39* T39 MG7 .72 .400 .535 4.394 .180 5. 03 0 T40 MG6 . 12 . 062 . 088 1.369 . 031 1.614 T40 MG7 . 13 . 066 . 098 1.303 .031 1.62 0 T41 MG6 .32 .205 .265 2.868 .080 3.634 T41 MG7 .26 .206 .239 3.227 .112 3.657 T42 MG6 .30 . 197 .250 2.907 .090 3.52* T42 MG7 .32 .230 .287 3.653 .122 3.84-9 T51 MG2 .21 . 084 .113 1.094 . 042 1. 090 T52 MG2 .36 . 132 . 177 1.705 .072 1. 047 T53 MG2 .23 .117 . 152 1.446 .062 1.200 T54 MG2 . 18 . 137 . 159 2.269 . 070 1.26*3 T55 MG2 .50 .237 .340 3. 252 . 125 1.367 T56 MG2 .76 .220 .303 2.365 .114 1.563 T57 MG2 .35 .243 .294 4. 001 .133 1.39-9 T58 MG2 . 07 . 037 . 045 .636 .020 .913 T59 MG2 . 16 . 046 . 071 .584 .021 .850 T60 MG2 .19 . 136 . 167 2.248 .082 1.231 ret MG3 .04 .026 . 031 .401 .020 1. 077 T62 MG2 .07 . 043 .055 . 696 .030 .98* T63 MG2 .54 .284 .367 4.612 .173 1.950 T64 MG2 .50 .279 .330 6.138 .185 2.331 T65 MG2 .10 - 054 . 066 .961 .040 1.245 T66 MG2 .20 . 063 . 087 .904 .030 1.002 T67 MG3 . 08 . 065 .072 tm 182 .041 1.233 : T68 MG3 .04 .026 .034 .405 .020 .823 .030 1.167 T69 MG3 . 06 .047 .053 .SIS i Table IX.1.2 (cont) Print from Permanent File RIPPLE pressures were recorded most frequently from traces from MG2 when up to seventy might be digitised from a 300 second section of trace. From all traces, it was noticed that the digitised shock pressures were not always close to the maximum pressures and were often of relatively low magnitude. 11.2 Wave Pressure Related to Wind Speed and Wave Height It was clear that the magnitude of the recorded wave pressures was related to wave height, although the form of the relationship was not known. It was also thought that wave pressures and wave height might be related to wind speed, but it was recognised that swell waves would probably be unrelated to local winds. However, Darbyshire and Draper (1963) and Shellard and Draper (1975) have related coastal and oceanic measurements of wave height to local wind speed, duration and fetch, thereby showing that useful correlations can be found. Wind speed was computed from the anemometer readings by program BREEZE (Fiche 1). This program also wrote the results, together with measurements of wave height to a permanent file called WIND, which is reproduced in Table 11.2.1. The wave pressure statistics from permanent file RIPPLE and the wind speed and wave height data from WIND were then used as the input to a program called PREP (Fiche 1) which prepared the data for plotting. This involved matching columns of the wave pressure statistics with the wind speed and wave height statistics for each site. The prepared data was then used as input to a short program (GRAPH 5 (Fiche 1)) which used library subroutines to produce microfilm plots of wind speed and wave height against wave pressure statistics for each, site. Prints of these plots are shown in Figures 11.2.1 to 11.2.6. For all the sites, it can be seen that there is a good linear 232 Col. 1 Date Col. 2 Trace No. Col. 3 Wind Speed (m.p.h.) over 24 hrs previous to recording Col. 4 Wind Speed (m.p.h.) during recording Col. 5 Wind Direction Col. 6 Wave height (m) offshore MG8, MG9 (Atlantic) Col. 7 Wave height (m) offshore UG6, MG7 (Culsetter Voe) Col. 8 Wave height (m) offshore MG2A (Sullora Voe) Col. 9 Wave height (m) offshore MG3A (Culsetter Voe) -1 or -1.00 refers to "no measurement taken". WED 30 MftY 1 2.40 3. 52 260 .30 . 05 -1. 00 — . 0 0 WED 30 MftY 2 2.49 1. 06 260 .30 . 05 -1. 00 - . DO THU 31 MftY 3 7. 09 20. 54 90 .20 . 15 -1. 00 - .00 THU 31 MftY 4 10.72 19. 98 70 . 15 .10 -1. 00 - . DO FRI 1 JUN 5 12. 08 19. 85 240 .50 . 05 -1. 00 - . DO SftT 2 JUN 6 10. 05 5. 32 120 .40 . 05 -1. 00 - • DO SUN 3 JUN 7 9.91 5. 68 120 .30 . 05 -1. 00 — .DO MDN 4 JUN 8 14.75 14. 79^ 170 .20 . 08 -1. 00 — • DO TUE JUN -1 8.40 -1. 00 140 .20 . 06 -1. 00 — .DO WED e JUN 9 4.74 5. 09 270 .20 . 08 -1. 00 — .DO THU 7 JUN 10 2.27 6. 82 30 .40 .09 00 - .00 FRI 8 JUN 11 8.14 13. 84 60 .20 . 05 -1. 00 - .DO SftT 9 JUN 12 3.65 8. 22 260 .30 . 06 -1. 00 — .DO SUN 10 JUN 13 12. 00 11. 56 260 .60 .10 -1. 00 - .DO TUE 12 JUN 14 3. 19 4. 23 270 .40 . 05 -1. 00 - .DO THU 14 JUN 15 3.66 7. 27 180 .60 . 15 -1. 00 — .DO FPI 15 JUN 16 3.71 12. 38 10 1 . 00 . 18 -1. 00 - .DO SRT 16 JUN 17 10. 19 15. 41 260 1 . 00 .28 -1. 00 - .DO SUN 17 JUN 18 15.79 19. 20 250 1 .00 .25 -1. 00 - .DO MDN 18 JUN 19 18. 15 17. 10 240 .80 .22 -1. 00 - .DO TUE 19 JUN 20 13. 06 9. 03 240 .70 . 14 -1. 00 — .DO WED 20 JUN 21 5. 19 16. 43 150 .30 .10 -1. 0 0 - .DO THU 21 JIJN 22 9.32 9. 94 170 .40 . 08 -1. 00 - .DO FPI 22 JUN 23 14.59 15. 98 210 .70 .22 -1. 00 — .00 SftT 23 JUN 24 7.24 3. 48 180 1 .60 .40 -1. 00 — .00 SUN 24 JUN 25 6.96 6. 33 130 .70 .10 -1. 00 - .00 MDN 25 JUN 26 5.93 9. 62 230 .70 . 14 -1. 00 - .00 TUE 26 JUN 27 16.83 14. 84 280 1 .80 .45 -1. 00 - .00 WED 27 JUN 28 9.37 10. 20 270 .80 . 16 -1. 00 — .00 TUE 11 SEP 31 16. 06 28. 90 290 3 .00 .55 -1. 00 — .00 WED 12 SEP 32 17.31 6. 34 220 1 .60 .25 -1. 00 - .00 THU 13 SEP 33 9.88 14. 31 310 1 .20 .28 -1. 00 — .00 FRI 14 SEP 34 7.23 5. 00 0 .60 . 13 -1. 00 — .00 SftT 15 SEP 35 9.63 6. 69 290 .60 . 16 -1. 00 — .00 SUN 16 SEP 36 12.51 28. 80 250 1 .00 .38 -1. 00 — .00 MdN 17 SEP 37 22.48 19. 10 240 1 .20 .42 -1. 00 - .00 TUE 18 SEP 38 25.53 34. 10 260 I -40 .38 -1. 00 - .00 WED 19 SEP 39 30.76 33. 26 270 3 .50 .65 -1. 00 — .00 THU 20 SEP 40 15.55 10. 11 80 .50 . 03 -1. 00 — .00 FRI 21 SEP 41 13.67 12. 10 320 .30 .24- -1. 00 — .00 SftT 22 SEP -1 4.71 -1. 00 220 .30 .08 -1. 00 —. .00 SUN 23 SEP 42 11.95 15. 44 280 .70 .26 -1. 00 — .oo ; FRI 28 SEP 17.48 -I. 00 280 1 .60 .32 -1. bo — .00 j SftT 29 SEP -1 2 •87 -1. 00 190 .80 . 10 -1. 00 — .00 J Table 11.2.1 Wind Speeds and Wave Heights at Mavis Grind Print from Permanent File WIND 2 33 SUM 30 SEP 51 2.28 12. 73 160 .50 . 05 .10 CI MDN 1 OCT 52 14. 12 19. 46 160 .40 . 12 .14 TUE 2 OCT 53 16.13 20. 14 150 .30 . 05 . 15 » WED 3 •CT 54 20.49 23. 71 150 .30 . 06 .18 0 THU 4 OCT 55 18.65 ; 31. 17 100 -1 .00 -1.00 .32 THU 4 •CT 56 20.62 26. 24 no . 15 . 10 .22 0 FRT 5 OCT 57 30.23 30. 24 120 .30 . 17 .35 0 SftT 6 OCT 58 19.28 4. 69 150 .30 . 06 .05 0 SUN 7 OCT 59 8.01 9. 21 150 .40 . 08 . 05 D MDN 8 OCT -1 3.87 -1. 00 555 . 15 . 03 0 0 TUE 9 OCT 60 4.85 18. 88 120 .30 . 07 .22 1) WED 10 OCT 61 4.87 17. 33 250 .40 . 14 0 . 02 THU 11 OCT 62 5.74 3. 27 80 .30 . 05 . 06 0 FRI 12 OCT -1 5.39 -1. 00 160 .30 . 06 . 07 0 SOT 13 •CT -1 .52 -1. 00 555 .30 . 05 0 0 SUN 14 •CT -1 .60 -1. 00 80 .30 . 05 .IS 1) MON 15 •CT 63 13.36 20. 25 40 -1 . 00 -1. 00 .40 1) MDN 15 •CT 64 14. 10 14. 95 30 .20 . 10 .40 0 TUE 16 •CT 65 6.96 3. 09 320 .50 . 12 . 04 0 WED 17 OCT 66 2.30 6. 48 200 .50 . 08 . 09 0 THU 18 •CT 67 19.89 21. 68 290 1 .70 .44 0 . 03 THU 13 •CT 68 20. 13 14. 80 260 2 . 00 .43 0 . 02 FRT 19 •CT 69 16.41 29. 16 250 2 .50 .52 0 . 03 Table 11.2.1 (cont) Wind Speeds and Wave Heights at Mavis Grind Print from Permanent File WIND " ' "imilw >«•« >N " * ' "junssTil l«o« "« ' lanssSA lAen "« Figure 11.2.1 Wind Speed and Wave Height vs. Wave Pressure for MG2A )" Jsim'V'B" oli" )«"{« >«<' V osi* ,-01" lifijsxj oii" i 5 '-f 1 'iwssl/t JA0M " 1! ' ')»n55°l«° No" 'iHI ' 'jJnstTA ')>•)«* ">it mnisim I«OK oiois 1»«« 0I3IS 'WMp ' "jnftss"?*^ JAd'JSn "innss'W in" JlS S 'lMllsSu MJ IN Figure 11.2.2 Wind Speed and Wave Height vs. Wave Pressure for MG2A I j»nss>m )»oh 3«nSC]ll4 3A0N I0U JWSSJUJ 1A«« Figure 11.2.3 Wind Speed and Wave Height vs. Wave Pressure for MG2A r-* I * I»nss'}»j nv'i Sn " • " Figure 11.2.4 Wind Speed and Wave Height vs. Wave Pressure for MG7 227 " JunssJiili 3»wt in " ' * 'j»nss°?»j J»<$ Sis Figure 11,2.5 Wind Speed and Wave Height vs. Wave Pressure for UG3 11 li* r?i2 i« iUnJ I'BS ISJ " ' '(•flttatl )«»» iu " ' " ' lnOltlu )><> 1*5 ""i i3! ' linsslli'j 3»o" r jri » )nntS?M W«M IM " ' IMlftSlM IMM >SU "'* UM IM Figure 11.2.6 Wind Speed and Wave Height vs. Wave Pressure for MG9 23 relationship between wave height and wave pressure, particularly if the significant pressure is used. Maximum wave pressures produce a similar relationship except for site MG2A where the relationship is blurred by a wider scatter of points. This is probably because this site is dominated by local wind-driven waves where the maximum pressures are usually provided by the chance occurrence of shock pressures. No relationships can be identified for MG3A due to insufficient data. The wind speed during the recording period is related to wave pressure only at site MG2A which is influenced by local wind-driven waves. The wave pressure at other sites appears to bear no relation to wind speed during or previous to the recording period. It was thought that the mean wind speed over the 24 hours previous to recording may provide an indication of the swell conditions at MG6 - MG9, but this does not appear to be the case. As expected, the wind speed previous to recording does not influence wave pressure at MG2A. It seems that when wind speed or wave height produce good correlations with wave pressure, similar relationships are produced by all the various wave pressure statistics with perhaps the exception of significant wave pressures. These produce slightly better relationships. It should also be noted that a weaker correlation is provided by maximum wave pressures for MG2A. In order to prevent undue repitition, it was decided that significant wave pressure would be selected as the main wave pressure measurement to be used for future data processing. 11.3 A Comparison of Wave Pressures Between Sites Since simultaneous measurements of wave pressures were taken from MG6 - MG9, it was possible to compare significant wave pressures from each of the sites for a particular recording session. Figure 11.3.1 shows the exposure grade of the sites related to the significant wave I Figure 11.3.1 Significant Wave Pressure va. Expoaure Grade 2,4/ 242 pressure obtained from each recording session. As can be seen from the graph (produced from a microfilm plot using program PREP 2 (Fiche 1)), a family of curves was produced which showed the relationship between exposure grade and wave pressure to be approximately inverse. On some occasions, the graphs did not follow this pattern, but in general, the difference in wave pressure between sites was greater in rougher wave conditions. Also the difference in wave pressure between sites at the exposed end of the exposure scale was greater than at the sheltered end. The very small difference between sites MG7 (Grade 3.50) and MG6 (Grade 4.50) is noteworthy. The inverse form of the relationship is clarified in Figure 11.3.2 which shows mean significant wave pressure plotted against the exposure grades of the sites. Mean significant wave pressures were also calculated for MG2A (Grade 7.00) and MG3A (Grade 7.75). Maximum wave pressures were also selected for each of the sites. They are shown in Table 11.3.1 below together with the maximum wave pressures and mean significant wave pressures for MG6 - MG9. Exposure Mean Sig Max Site Grade Pressure Pressure MG9 1.75 0.676 2.03 MG8 2.00 0.509 1.78 MG7 3.50 0.150 0.72 MG6 4.50 0.141 0.67 MG2A (7.00) 0.141 0.76 MG3A 7.75 0.041 0.06 Table 11.3.1 Maximum and Mean Significant Wave Pressures It must be pointed out that the means for MG2A and MG3A are not cora- patable to the means from MG6 - MG9 because they were not obtained sim- ultaneously. Also, they represent a biased sample because recording only took place when the wind was blowing to produce waves. A comparison between sites dominated by wind-driven waves (MG2A, MG3A) and sites pressure in PSI Figure 11.3.2 Maximum wave pressure and mean significant wave pressure vs. exposure grade The upper curve is for maximum recorded wave pressures, and the lower for mean significant wave pressures, based on simultaneous recordings made at the four sites MG6 to MG9. It is not possible to extrapolate reliably beyond the observed values into conditions of extreme wave exposure from this figure, but it is obvious that pressure values for a grade 0 shore would be very much in excess of those actually recorded. There would appear to be an inverse and possibly exponential relationship between the two variables. 244 dominated by swell (MG6 - MG9) would only be possible by extrapolating the records over at least a year and then reducing the data through an integrating medium such as the percentage exceedence curve. This approach is considered in section 11.4. As an attempt to compare wave forms between sites, the mean wave form from a number of traces was computed using subroutine FORM within a version of program FORCE. The technique was to scan the data once and extract the maximum duration of a wave. This was then divided into a number of intervals (INC) in which the mean wave form was plotted on microfilm by subroutine GRAPH (see program FORCE 3, Fiche 1). Traces 31, 57, 67, 78 and 91 were averaged in this way. Initially, eight intervals (INC) were used in the computation, but slightly better results were obtained with ten intervals. With either eight or ten intervals, the results of the analysis were not very satisfactory because the wave forms were too spikey and tended to have a double peak over a wave duration that appeared to be too long. This was thought to be due to the excessive influence of the few unusual waves. To overcome this, the wave form was terminated where the intervals contained less than 15 points, and the mean wave form was recalculated over this new wave duration. This seemed to solve the problem of unrealistic double peaks, and produced more representative wave forms (Figures 11.3.3. - 11.3.6). Figure 11.3.3 shows the mean wave forms from MG6 - MG9 during rough conditions, and Figure 11.3.4 shows the mean wave forms from MG2A and MG3A under similarly rough conditions. They are all plotted on the same axes for comparability. As is typical with longer wavelength swell, the wave forms from MG6 - MG9 occur over a longer duration than those from MG2A and MG3A which are produced from shorter wavelength wind-driven waves. The overall magnitude of the wave forms from MG9 and MG8 are 249 much larger than those from MG7 and MG6, while the overall magnitude of the latter are not very different from the wave form from MG2A. The main difference between the wave forms from MG2A compared to MG7 and MG6 is that the latter have longer durations. The wave form from MG3A is very small over a short duration. Figure 11.3.5 shows the mean wave forms from the four transducers located in different positions on MG9. The normally mounted transducer (NOR) has an unrealistic double peak, but if the second peak is considered to be a repitition of the first, the wave form is similar to that for the transducer in the gulley (GUL). The transducer mounted flat (FLA) produces a characteristically smaller magnitude wave form, whereas the transducer mounted vertically (VER) has a more spikey wave form due presumably to the influence of shock pressures. Figure 11.3.6 shows the mean wave forms from the four transducers located in similar positions on 0P70. The wave form from VER has a greater magnitude than that from NOR whereas the wave form from FLA is of smaller magnitude over a longer duration. The wave form from GUL has the longest duration because the waves in this gulley were in the form of long wavelength oscillations in water level. 11.4 Extrapolation of the Wave Pressure Records In order to have reliable estimates of the relative wave exposure status of the various sites, an attempt was made to extrapolate the short term wave pressure records over a suitably long time period such that representative wave pressures for each of the sites might be extracted and compared. Saetre (1974), in considering extreme wave heights, adopted the probability approach used by Weibull (1951) and others whereby the probability of the measured wave heights occurring is cal- culated, plotted against wave height, and extrapolated. Since it seems likely 250 that the ecology of the shore responds more to the continuity of wave action rather than the maximum wave pressure, the percentage exceedence approach used by Draper (1967) and Draper and Squite (1967) seemed to be a simpler and clearer way of expressing the long-term distribution of wave pressures at the various sites. The first stage, however, was to relate wave pressure to a suitable variable which had been measured over a longer time scale. In the case of a site dominated purely by local wind-driven waves, a suitable variable would appear to be wind speed, whereas in the case of a site dominated by swell, that variable would have to be wave height (c.f. section 11.2). As test cases, an extrapolation technique was applied to MG2A to represent a site dominated by local wind-driven waves, and to MG8 to represent a site dominated by swell. It has already been shown in Section 11.2 that wave pressure at MG2A is closely related to wave height (the correlation coefficient is 0.977 for fifteen points) and also to wind speed measured during the recording period. Since long-term wind data was available from Lerwick Observatory, an attempt was made to relate wave pressure and wind speed recorded at Mavis Grind to wind speed recorded at Lerwick, 30 km. away. The relevant data is shown in Table 11.4.1, and plots relating wind speed to wave pressure are given in Figures 11.4,1 to 11.4.3. It can be seen from Figure 11.4.1 that there is a good correlation (r = 0.772, significant at p - 0.005 for fifteen points) between sig- nificant wave pressure and wind speed recorded at Mavis Grind. The regression line (Y = 0.0230 + 0.0073 X) has not been forced through the origin since it is likely that very small wind speeds might not be recorded on the anemometer (c.f. section 10.4) although they might produce small waves at MG2A. The T ratio for the slope of the regression is 10.37 Mavis Significant Grind Lerwick Wave Wind Wind Pressure Speed Speed PSI m.p.h. knots 0.084 12.73 14.00 0.132 19.46 15.00 0.117 20.14 19.00 0.137 23.71 20.00 0.237 31.17 23.00 0.220 26.24 24.00 0.243 30.24 26.00 0.037 4.69 11.00 0.046 8.21 13.00 0.136 18.88 14.00 0.043 3.27 5.00 0.284 20.25 20.00 0.278 14.95 20.00 0.054 3.09 10.00 0.063 6.48 22.00 Table 11.4,1 Wave Pressure and Wind Speed at MG2A with Wind Speed at Lerwick Figure 11.4.1 Significant Wave Pressure vs. Mavis Grind Wind Speed - MG2A 2?Z Figure 11,4.2 Mavia Grind Wind Speed at MG2A vs. Lerwick Wind Speed Figure 11.4.3 Significant Wave Pressure vs, Lerwick Wind Speed - MG2A 255 which is significant at p = 0.00001. Figure 11.4.2 shows that there is a fairly wide scatter of points when Mavis Grind wind speed is compared to Lerwick wind speed. Nevertheless, Lerwick wind speed was related to significant wave pressure at MG2A as shown in Figure 11.4.3. As expected, there was a similarly wide scatter of points, although the two variables were significantly correlated (r = 0.733, significant at p = 0.005 for fifteen points). In this case the regression line (Y = 0.0085 X) was forced through the origin since more confidence could be attributed to the accuracy of the anemometer at Lerwick. The slope of the regression line was significantly different from zero, as shown by the T ratio of 9.45 which is significant at p = 0.00001. Nevertheless, the wide scatter of points in this regression gave cause for concern, and a different relationship was sought. From Figure 11.4.1, the two points that appear to be anomalous were produced when the wind was blowing strongly over the maximum fetch to MG2A. It must be remembered that for most of the recording period, the wind was blowing from the south-east over a limited fetch to MG2A and consequently the significant wave pressures were lower. In order to incorporate the influence of fetch into the regressions, multiple regressions were produced using wind speed (X^) and fetch as follows: i) Mavis Grind Wind Speed Y = 0.798 X + 4.149 2 R' 0.637 F 22.788 NDF1 = 1, NDF2 = 13 Significant at 1% ii) Mavis Grind Wind Speed and Fetch Y 0.381 Xx - 0.292 X2 + 0.491 2 R' 0.053 F 0.334 NDF1 = 2, NDF2 = 12 Insignificant at 5%. 256 iii) Lerwick Wind Speed Y = 0.733X + 10.251 R2 = 0.538 F = 15.132 NDF1 = 1, NDF2 = 13 Significant at 1% iv) Lerwick Wind Speed and Fetch Y = -0.324X1 + 0.524X2 + 0.133 R2 = 0.130 F =0.901 NDF1 = 2, NDF2 = 12 Insignificant at 5% 2 It can be seen that the proportion of the variance (R ) in significant wave pressure accounted for by wind speed alone was 63.7% in the case of Mavis Grind wind speed and 53.8% in the case of Lerwick wind speed. The addition of fetch to the regressions surprisingly caused a dramatic 2 drop in R . This may be due to the fact that a single estimate of fetch was inappropriate because of small shifts in wind direction and refraction allowing larger waves than might be expected. As an attempt to counteract this, the effective fetch (U.S. Army, 1966) for each wind direction for MG2A was calculated as follows: For each wind direction, lines were drawn on a map at 6° intervals over an arc of 45° to either side of the wind direction. The fetch on each line was measured and multiplied by the cosine of the angle from the wind direction. The sum of these products was then divided by the sums of the cosines of the angles to produce the effective fetch for that wind direction. Values of the effective fetch (X2), wind speed (X^)and significant wave pressure (Y) were then used for the calculation of the following multiple regressions: i) Mavis Grind Wind Speed and Effective Fetch Y = 0.875XX - 0.359X2 + 0.183 R2 = 0.409 F =4.153 NDF1 = 2, NDF2 = 12 Significant at 5% 257 ii) Lerwick Wind Speed and Effective Fetch Y = -0.073X1 + 0.551X2 - 0.147 R2 = 0.250 F =1.995 NDF1 = 2, NDF2 = 12 Insignificant at 5% 2 From the values of R , it can be seen that by replacing fetch with the effective fetch, the proportion of the variance in significant wave pressure accounted for by the regression was increased. However, the 2 variance-ratio test (F) indicated that these values of R were not very significant, even at the 5% probability level. This showed that the multiple regression approach could not be confidently applied to this data. It seemed that the relationship between wind speed at Lerwick and significant wave pressure at MG2A could not be reliably used to extra- polate wave pressures. However, some idea of the representativeness of the wave pressures at MG2A could be estimated from long term wind speed records available from Lerwick over the period 1957 to 1978 (Table 11.4.2). Bearing in mind that the wind only produced waves at MG2A from the direction 011°-220°, a percentage exceedence curve for effective wind speeds was constructed (Figure 11.4.4). Wave pressures at MG2A were recorded during Lerwick wind speeds ranging from 5 to 26 knots, thereby indicating that wave pressures from all but the top 3.7% of wind speeds had been recorded. MG8 is a site that is dominated by a mixture of swell waves and locally generated waves. Consequently the significant wave pressure bears little or no relation to the local wind speed, although as with all sites there is a good relationship with local wave height (Figure 11.4.5, plotted by program GRAPH 7 (Fiche 1)). Long term records of wave height have been taken from two locations near to Shetland. The U.K. Offshore Operators Association (UK00A) set up a station named 258 DIR 341 Oil 041 071 101 131 161 191 221 251 231 311 WINDV SPEED \ 010 040 070 100 130 160 190 220 250 280 310 340 TOTAL CALM 4.2 '4.2 1- 3 0.3 0.3 0.2 0.2 0.2 0.3 0.4 0.5 0.3 0.3 0.3 0.5 3.8 4- 6 0.8 0.7 0.6 0.5 0.5 1.1 1.2 1.1 0.8 1.0 1.0 1.2 10.5 7-10 2.1 1.5 1.0 0.9 1.2 2.2 2.9 1.6 1.8 2.1 2.0 2.1 21.4 11-16 2.5 2.1 1.2 0.9 1.7 2.7 4.0 2.4 3.4 2.7 2.2 2.5 28.3 17-21 1.2 1.1 0.5 0.4 0.9 1.6 2.0 1.7 2.5 1.7 1.0 1.1 15.7 22-27 0.6 0.6 0.2 0.2 0.6 1.1 1.4 1.4 2.1 1.3 0.5 0.5 10.5 28-33 0.2 0.2 0.1 0.1 0.3 0.5 0.6 0.6 0.9 0.6 0.2 0.2 4.5 34-40 0.1 0.1 0.0 0.0 0.0 0.2 0.2 0.2 0.3 0.3 0.1 0.1 1.6 41-47 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.0 0.0 0.2 TOTAL 7.8 6.6 3.8 3.2 5.4 9.7 12.7 9.5 12.2 10.1 7.3 8.2 100.7 Table 11,4.2 Annual Hourly y£ Frequency Wind Speeds Lerwick 1957 - 1978 259 Percentage Exceedence 60 w \ 10 20 30 40 Wind Speed (knots) Figure 11.4.4 Percentage Exceedence Curve of Wind Speed Effective for Producing Waves at MG2A (Lerwick Data) 260 Fitzroy to the west of Shetland at a point about 30 km. south-west of Foula (60 10' N, 2 20*W) . Wave height was recorded at frequent in- tervals using a shipborne wave recorder and later a waverider buoy over the period December 1973 - November 1978. The Shetland Islands Council (SIC) have been recording wave heights from three waverider buoys in Yell Sound since September 1976. The most northerly waverider buoy is situated near to Ramna Stacks (60° 20fN, 1° 20'W) and consequently records swell from a northerly and westerly direction. Wave height data from Fitzroy, Yell Sound, and MG8 are given in Table 11.4.3. Plots relating Yell wave height to MG8 wave height, and Yell wave height to MG8 significant wave pressure are given in Figures 11.4.6 and 11.4.7 respectively (plotted by GRAPH 7 (Fiche 1)). As expected from Figure 11.4.5, the plots are similar and would show a good linear re- lationship but for three anomalous points. These were produced by easterly winds which allowed a relatively higher wave height at the Yell station than at Mavis Grind. Consequently the significant wave pressure at MG8 appears low compared to the Yell wave height. The correlation coefficient between the two variables is 0.346 which is insignificant, with 21 data points, at a probability of less than 10%. Plots relating Fitzroy (Foula) wave height to MG8 wave height, and Foula wave height to MG8 significant wave pressure are given in Figures 11.4.8 and 11.4.9 (plotted by program GRAPH 7 (Fiche 1)). With correlation coefficients of 0.545 and 0.695 respectively, the variables are significantly correlated (p = 0.001), although the wide scatter of points on the Fitzroy (Foula) wave height vs. MG8 wave height plot does not inspire confidence in the relationship. The apparently better relationship on the Fitzroy (Foula) wave height vs. MG8 significant wave pressure plot is deceiving because fewer wave pressure records were taken during a period of south-easterly winds which provide a 261 Mavis Fitzroy Yell Significant Grind (Foula) Sound Wave Wave Wave Wave Pressure Height Height Height 0.167 0.20 1,75 1.07 0.090 0.15 1.81 1.07 0.373 0.50 1.44 0.79 0.326 0.40 0.88 0.53 0.234 0.30 1.11 0.59 0.126 0.20 1.52 0.70 - 0.20 1.34 0.40 0.292 0.20 1.10 0.40 0.417 0.40 1.06 0.69 0.177 0.20 2.03 1.58 0.198 0.30 0.83 0.76 0.397 0.60 0.96 0.86 0.271 0.40 0.82 0.50 0.447 0.60 1.38 0.50 0.781 1.00 2.87 1.18 0.680 1.00 1.90 1.21 0.857 1.00 2.28 1.39 0.678 0.80 1.96 0.99 0.618 0.70 1.99 0.83 0.305 0.30 1.53 0.60 0.391 0.40 1.42 0.54 0.652 0.70 2.68 1.02 1.089 1.60 3.99 0.406 0.70 2.03 0.482 0.70 2.14 0.884 1.80 5.29 0.576 0.80 2.11 1.218 3.00 3.04 0.727 1.60 2.85 0.623 1.20 4.32 0.449 0.60 2.45 0.562 0.60 3.68 0.806 1.00 2.98 1.20 4.13 1.40 3.76 3.50 5.19 0.50 2.70 0.80 3.98 0.30 3.76 0.70 2.76 1.60 2.82 0.80 2.45 0.50 2.40 0.40 3.35 0.30 3.01 0.30 3.52 0.15 3.11 0.30 4.91 0.30 3.87 0.40 2.25 0.15 1.74 Table 11.4.3 Significant 0.30 1.67 Wave Pressures at MG8 0.40 1.91 and Simultaneous r 0.30 2.01 Wave Heights 0.30 3.14 0.30 1.93 0.20 3.01 0.5*0 1.41 2. 6o CO z: I lc o o e o e a e 6 8 09-1 or. or i 02-1 or i oo-1 °3 ^SS3^ "3°AbM ^ ^ 5F5 ^o ^ oo-^cP Figure 11.4.5 Significant Wave Pressure - UG8 - vs. MG8 Wave Height Ul I CO CD XI o o ! 00" I >6"0 08-0 •i.-O 09'0 >9"0 0 OrO C£"0 02'0 ECO LO'O OO'cP L9-0 L9-0 1H0I3H 3Ab M LfQW LZ'O Figure 11,4.6 MG8 Wave Height vs. Yell Wave Height 2Ci i CO 2 ;^^^ ^ ^ 5775 570 ^ ^—^—^— i Figure 11.4.7 Significant Ware Pressure - UGQ - vs. Yell Wave Height CO r h, o r- 8 o i.' f 9* e 82-e l S- Figure 11.4.8 MG8 Wave Height vs. Foula (Fitgroy) Wave Height Oft OEM 02M 01 - I 00"! 06*0 08"0 Oi'O 3ynss3yd 3AOM OIS Figure 11.4.9 Significant Wave Pressure - MG8 - vs. Foula (Fitzroy) Wave Height 267 series of points on the bottom right corner of the Foula wave height vs. MG8 wave height plot. The lack of a good relationship between the three estimates of wave height is illustrated by reference to Figure 11.4.10 which shows a time-series of wave heights from MG8, Yell Sound, and Fitzroy (Foula)- This is particularly noticeable during a period of south-easterly winds in October 79 when Fitzroy (Foula) wave heights were large in comparison to wave heights from the Yell Sound and MG8 stations which were sheltered by the Shetland Islands. The poor correlation between the three estimates of wave height must be becuase coastal configuration and the sheltering effect of the islands considerably modifies the wave environment from open sea conditions. Neither the Fitzroy (Foula) wave height nor the Yell wave height relationship with significant wave pressure at MG8 seemed strong enough for the extrapolation of wave pressure records. However, some idea of the representativeness of the traces from MG8 may be obtained from the percentage exceedence wave height graph for Fitzroy (Foula) (Figure 11.4.11). During the recording period at MG8, wave heights at Foula ranged from 0.75 m. to 5.25 m. From the percentage exceedence graph, it can be seen that this covered all but the top 9.5% of significant wave heights at Fitzroy which sometimes rise up to 10.5 m. It therefore seemed likely that larger wave heights and consequently wave pressures than were measured might occasionally occur at MG6 - MG9 during storms. At MG2A, wave pressure measurements were taken from all but the top 3.7% of wind speeds, whereas at MG6 - MG9, pressure measurements were taken from all but the top 9.5% wave heights. Therefore, it seemed likely that the maximum wave pressure at MG2A was more nearly attained than at MG6 - MG9. / / -I Xo to ir*4) Significant Wave Height Foula (Fitzroy) Significant Wave Height Yell Figure 11.4.10 Time Series of Estimated Wave Height Mavis Grind Wave Heights WAV£ wgiqu-r t* 4 r x II st? TO S€? SO I ^ oc- mi s£?r oar Significant Wave Height Foula (Fitzroy) Significant Wavo Height Yell figure 11.4.10 {cont) The Series of Estimated Wave Height Mavis Grind K3 Wave Heights o\ VO 270 Percentage Exceedence Hs m. Significant Wave Height Figure 11.4.11 Percentage Exceedence Curve of Wave Height for Fitzroy (Foula)* Dec 1973 - Nov 1978 271 CHAPTER 12 Measurement of Wave Action - Discussion and Conclusions From the outset, it was assumed that an ecologically relevant estimate of wave action would be provided by the measurement of wave impact pressures. Wave impact pressures had been measured in the past mainly for engineering purposes, and de Rouville et al (1938) had developed suitable equipment for measuring various components of the wave impact. The main requirement of wave pressure measuring equipment is that it can record the short duration, high intensity shock pressures that are known to occur usually at the beginning of the wave form. Because of this, the instruments that were selected for the present study were remarkably similar in principle to those used by de Rouville et al. Recent technology accounted for certain differences such as the use of a silicon semiconductor instead of a quartz piezoelectric crystal as the basic sensing element in the transducer. For the recording part of the instruments used in this study, manufactured equipment was available which combined and streamlined many components used by de Rouville et al. The various transformers and amplifiers were available in a compact and smaller unit. Similarly, the principle of reflecting a light beam on to photographic paper had been developed into a compact and portable recording instrument in the form of the BHL Minigraph. Furthermore, the output from this was on direct print paper rather than on photographic film used by de Rouville et al. Another advance was that the whole system could be powered by a 12 V battery, resulting in a light, compact and easily transportable system for measuring wave pressures. During the simultaneous measurement of wave pressures in Shetland, the method of attaching the transducers to the shore was improved after the backing plates had become detached during rough conditions. Initial problems of seawater seepage into the transducers were also solved, 272 and the equipment appeared to function satisfactorily. Wave impact pressures measured from MG6 - MG9 were much smaller than those that had been obtained from similar sized waves by de Rouville et al in 1938, the main difference being in the magnitude of the shock pressures. Shock pressures of up to 100 PSI were recorded by de Rouville et al from waves of 3.50 m. in height breaking against the base of a harbour wall at Dieppe. On the rocky shore in Shetland, the maximum shock pressure obtained was 4.55 PSI from a similar sized wave. As mentioned by Bagnold (1939) and Denny (1951), it seems that the occurrence of extreme shock pressures depends upon the type of wave and the nature of the receiving shoreline or obstruction. Ideal conditions for the entrapment of an air pocket and production of extreme shock pressures occur when waves begin to break slightly before they hit the even surface of a vertical or steeply sloping harbour wall. The irregularities of the natural shoreline make the chance of extreme shock pressures very rare, even if the sensor is placed in a likely place for their occurrence. Locating the transducer on a vertical surface at the back of a rock step did produce more shock pressures than a transducer mounted on an open surface of rock, but the magnitude of the shock pressures were rarely greater than the hydrostatic pressure of water in the wave. Fuhrboten (1970) points out that foaming and air entrainment generally causes a large reduction in wave energy from breakers. This may explain differences in wave impacts on a breakwater and natural shoreline, since- foaming is more prominent on the latter. Miller et al (1974) recorded wave impact pressures in the field with their pressure sensors mounted on a vertical pole. They also did not record extreme shock pressures presumably because the supporting structure of the pole was not conducive to their formation. 273 Wave pressures were also measured at a more sheltered location in Shetland (MG2A) where there was no swell and waves only occurred when the wind was blowing from a suitable direction. The wind-driven waves ware more regular and had a shorter wave period than swell waves. They also appeared to curl over and slap down on to the shore in contrast to small swell waves which would merely rise up and down against the shore. Consequently more and greater shock pressures were recorded at MG2A than at MG6 or MG7, although their overall magnitude was never more than about twice the impulse due to the hydrostatic pressure of water in the wave. Instrument testing has shown that there appears to be no reason to doubt that the wave pressure measuring equipment has accurately recorded wave impacts on the shoreline. Although it is likely that extreme shock pressures do not occur on rocky shores, they must be extremely rare for any particular spot because only relatively small shock pressures were in fact encountered over many hours of recording. These smaller shock pressures do appear to be caused by air entrapment in the same way as extreme shock pressures because the characteristic oscillations described by Kamel (1971) were found. Kamel relates these fluctuations to the repeated expansion and compression of the air pocket in the form of a damped oscillation. A notable difference between conditions at MG2A and MG6 - MG9 is that at the former location waves were only produced infrequently when the wind was blowing from a suitable direction. On these occasions, a large number of shock pressures occurred. At MG6 - MG9, there were fewer shock pressures but there was constant water movement due to swell. Since the magnitude of wave impact pressures were rather low, it has been hypothesised that perhaps the water movement due to swell is a more important ecological factor than actual wave impact. If this 274 is the case, the wave pressure measurements have not been invalidated 'j since the rate of water movement is likely to depend on the wave impact .< forces, however small they might be. The wave pressure traces were digitised, and significant wave i ; pressure was chosen as the most useful statistic to be extracted. A 1 i comparison of the simultaneous significant wave pressures from MG6 - MG9 V -i , - ] revealed that there was an approximately inverse relationship between pressure and exposure grade. In relating wave pressure records from i MG2A and MG3A to those from MG6 - MG9, the maximum significant wave i pressures from the various sites were compared, bearing in mind the : !j representativeness of the records. Wave pressure records had been ; taken from MG6 - MG9 over all but the highest 9.5% wave heights from ,"> Fitzroy, and from MG2A over all but the highest 3.7% wind speeds from Lerwick. If the maximum significant wave pressure could be used as !j an estimate of the wave exposure stat us of a site, it follows from } the percentages given above, that this value for MG2A would have to ; I be decreased for comparable conditions to the maximum recorded for MG6 - MG9. In this case, the maximum significant wave pressure for site » MG2A would fall into the approximately inverse relationship between | significant wave pressure and exposure grade, and consequently reinforces ! the validity of the relationship. j Finally, it should be emphasised that unexpected responses of the * equipment have been checked and there is no reason to doubt their valid- s'; ity, that placing the transducers at different angles to the incoming ^ waves (including placing on a vertical face) led to very little differ- ence in the pressure traces, and that the much lower-than-expected values obtained may be attributed to energy loss on an irregular rocky shore (as ' ! o discussed on p. 372). Results from placing the transducers at approx. 30 to the horizontal, whatever is actually measured, are nevertheless compar- able from site to site. \ PART IV SPECIES CHARACTERISTICS IN RELATION TO WAVE ACTION 275 CHAPTER 13 13.1 Introduction Over the range of rocky shore environments from exposed shores to ones sheltered from wave action, the morphology of some species is clearly adapted to allow them to be more universal or to capitalise on certain situations. For both the flora and fauna, sheltered con- ditions usually provide an opportunity for individuals to grow to a large size and to take maximum advantage of the favourable environment. In extending their distribution to more exposed shores, most species have evolved smaller forms or more streamlined shapes to withstand the damaging effects of wave action. Barnacles and mussels have developed adequate attachment methods so that they are ubiquitous over the exposure range, and very large individuals of MytHus edulis may be found in sheltered conditions. The littorinids and Gibbula cCnevavia are generally restricted to sheltered conditions because of their feeding habits and morphology, although small forms of the Littorina saxataHs aggregate occur on exposed shores in suitably sheltered barnacle shells or crevices. NuceHa lap'CVius is an example of a gastropod that has developed distinct populations different in morphology depending on location. In sheltered areas, individuals grow fairly large, and are elongated in form with a pronounced spire and a narrow aperture. In exposed areas, greater powers of adherence to the rock are required, and consequently they are smaller, with a more squat shell and a wider aperture (Crothers, 1973). J.H. Crother's work on the shell shape of Nueella lapilhis will be considered in more detail in section 13.2. Similarly, observations on limpets in Shetland indicate that large, tall limpets with a circular base are typically found in sheltered locations, whereas they are usually 276 smaller and more squat in more exposed locations. In addition, the base of the shell appears to be more elliptical and usually orientated to provide least resistance to the normal flow of water over the rock. It seems that a more objective study of the shell shape of limpets in relation to exposure would be worthwhile. The only large alga to be found in very exposed areas is Alaria esoutenta. Its morphology is ideally suited to its environment in that it is streamlined and bends easily with the direction of water movement. It has a long flexible stipe with a reduced frond area flanking it. Laminaria digitata is a species which occurs over a wide range of exposure conditions. In very sheltered areas, the broad, laminar frond spreads out over a wide area to take maximum advantage of the available illumination. At sites with greater wave exposure, the shape of L. digitata becomes more similar to that of Alaria esculenta in order to provide the least resistance to wave action. The frond becomes longer and thinner so that in very exposed locations a separate form of the species may be recognised - L. digitata f. stenaphylla. This change in morphology over the exposure range is considered in Section 13.3. Many algal species that grow in exposed locations are short and tufty as is demonstrated by species such as Corallina officinalis and Gigartina stellata. These species are also found in the same form in more sheltered conditions. Various algae such as the fucoids grow to a large size in sheltered conditions in response to the favourable conditions for growth. In more exposed areas, these larger algae develop into smaller forms as a response to being damaged by wave action. In fact, a distinct dwarf version of Fucus spiralis known as F. spiralis f. nanus has been recognised from exposed shores although it was only 277 recorded from one site in Shetland (Sandness, SH30). The larger forms of Fuaus vesiculosus in sheltered areas are covered by a great many vesicles giving buoyancy and allowing the plant greater access to nutrients and light. In more exposed areas, vesicles are a disadvantage because they give greater resistance to water movement and so lead to fronds being damaged. Thus plants in more exposed locations have fewer vesicles and are also much smaller. Burrows and Lodge (1951) described three forms of F. vesiculosus relating principally to the density of vesicles on the fronds. In order of decreasing vesicles and size, these are: var vadorum3 var vesiculosus and var evisiculosus (now f. linearis). The most extreme form is F. vesiculosus f. linearis which has no vesicles and exists on moderately exposed shores. The relationship between vesiculation of F. vesiculosus and exposure grade will be examined in Section 13.4. Some algae have changes in morphology in sheltered conditions which are less easily explained in terms of wave action. Kain (1976) has described hollow-stiped Laminaria sp. which were found only in the most sheltered locations in Shetland. Stipe length increased with increasing shelter and the hollow in the stipe only occurred in those individuals with the longest stipes. A possible explanation of this development might be that air in the stipe adds to the buoyancy of the larger plants, thus allowing them to capitalise on the sheltered conditions. Another phenonemum in very sheltered situations is the occurrence of "free-living" forms of Asoophyllum nodosum and Fucus servatus, As already mentioned in Section 2.2, the development of these forms may be due more to a reduction in salinity than shelter from wave action. Whereas variation in the shell shape of some gastropods can be easily explained in terms of wave exposure, Berry (1974) has discovered a mysterious correlation between the colour banding of dog-whelk shells 278 and exposure to wave action in Shetland. It seems that more coloured and banded forms exist in more exposed locations, and that the change in frequency of banded whelks can occur over a short distance in accordance with a rapid change in wave exposure. The reason for this change in morphology with wave exposure has yet to be discovered. 13.2 Nuoetla lapillus Crothers (1973) first documented variation in the shell shape of Nuoetla lapiHus from populat ions in Dyfed, South Wales. He found that short squat dog-whelks were commonly found on exposed shores while larger specimens with a more pronounced spire were found in sheltered areas. He reasoned that the large variation in shell shape between the sites was possible because the dog-whelk lacks a planktonic dispersal stage and therefore exists in discrete breeding units which evolve to suit the surrounding environment. Whereas the dog-whelk may grow to a large size in sheltered areas, short squat shells are obviously an advantage on exposed shores since the wider mouth would provide greater adherence to the rock surface. Crothers (1973) quantified the shape of the dog-whelk shell by measuring the total length of the shell (L) and expressing it as a ratio of the aperture length (Ap). At each site, samples of 100 shells were taken for measurement, while the wave exposure status of the site was estimated on Ballantinefs (1961) exposure scale. From sixty samples, he found that the relationship between exposure grade and shell shape (L/Ap) was best described by a linear regression as reproduced in Figure 13.2.1. A similar relationship was found to exist from studies on dog-whelks from other areas in western Europe (Crothers, 1974; 1975a; 1975b; 1977) including the Mongstad area of Norway (Dalby et al, 1978). It seemed likely that a similar relationship would be found for Shetland. 279 L/Ap 1.5 1.4 1.3 1.2 5 6 7 Exposure Grade Figure 13.2.1 Variation in the shape of Pembrokeshire (Dyfed) Populations of Nucella lapillus with exposure. Drawn after Crothers (1973) l/Ap 1.5 • .* »» 1.4 1.3 12 345678 Exposure Grade Figure 13.2.2 Variation in the Shape of Shetland Populations of Nucella lapillus. Drawn after Crothers (1979) 280 Dog-whelk samples were taken from 102 sites over a wide exposure range in Shetland (Crothers, 1979). They included sites that had been established by OPRU and myself, and consequently exposure grades computed from the Shetland exposure scale were available. Crothers (1979) plotted Shetland exposure grade against the shell shape ratio (L/Ap) as re- produced in Figure 13.2.2. He found that there was a weaker relationship between exposure grade and shell shape for Shetland compared to other areas in western Europe. It seemed that whereas very exposed sites supported only the short squat form of dog-whelk, the more elongated form was present over a wider range of exposure than elsewhere. The reason for the existance of elongated forms in areas of moderate exposure is far from clear, although the following hypothesis might be applicable. It has already been mentioned that shores of moderate exposure (Grades 3-5) in Shetland appear to be dominated by a continuous residual swell of small wave height. Shores biologically graded as being moderately exposed must be in a situation to allow the penetration of swell, but may not have a large fetch (c.f. MG6, MG7). The biological importance of continuous water movement provided by swell may be that the planktonic larvae and spores of the majority of rocky shore species do not easily attach to the shore under these conditions. In contrast, the egg capsules of the dog-whelk would be easily attached, and thus any forms of the dog-whelk would be able to become established. Survival would be assured as long as there were no freak waves in these areas of continuous small swell, classified by other species to be moderately exposed in Shetland. If moderately exposed shores in other geographical locations are caused more by the occasional occurrence of larger wind-driven waves over a larger fetch, the elongated form of the dog-whelk would be more easily knocked off the shore on these occasions, and would have less chance of surviving. More research into the way in which wave action influences different species is clearly required. It would also be worthwhile to 281 investigate the wave climate of different geographical areas that have been given the same biological exposure grade. 13.3 Laminaria digitata Laminaria digitata is a lower shore alga that occurs over a wide range of exposure conditions in Shetland. Reference to its abundance curve in Ficue 2 shows that its abundance is "occasional" (or abundance score 2) or more over the exposure range Grade 1.00 to Grade 6.75. In sheltered conditions it is a large plant with a wide rubber-like lamina on the end of a usually short stipe. In increasingly exposed situations, the frond becomes narrower on a longer stipe. In very exposed situations, the frond is so long and thin that it justifies separate classification as L. digitata f. stenaphylla (Figure 13.3.1). A means of measuring this change in morphology was provided by the angle subtended by the base of the lamina from the point where it emerges from the stipe. The large L. digitata frond is the sporophyte generation in the life-cycle of the plant. The gametophyte is microscopic and filamentous (Boney, 1966). Growth of the sporophyte is seasonal, being fast from January to June, and slower for the rest of the year. The lamina grows from the stipe end, while the distal end becomes battered and worn away by wave action. During the second half of the year, the lamina thus appears to be much more battered than at the beginning of the year when faster growth pushes the old battered lamina further towards the distal end of the plant. The angle subtended by the lamina base varies depending on the speed of growth and therefore upon season. For comparability purposes, it was therefore important that all the plants were measured at a similar time of year - March 1980 was chosen for this study. Samples of Laminaria digitata were taken from fourteen sites in Shetland. Accurate measurement in the field was impossible because 282 Laminaria digitat~ r. stenaphylle. Exposed Shore Form Form T-.;pically Found on 1loderately Exposed Shores Sheltered Shore Form Figure 13.3.1 Variation in Morphology or Laminaria digitata with Exposure to ~ave Action 283 SH22 ill 1.50 MG9 1.75 Ji MG3 2.00 1L 0P67 2.50 1_1_L 'III.II MG7 3.50 II 0P68 3.50 1_L 0P70 3.75 I I 1 OP69 4.25 > 1 t mill 111 MG6 4.50 in J LUL SH24 4.50 I f I 1 I I I I 1 f I I L-l MGX 4.75 J L I I 1 1 I « > i } SH21 6.00 j L I 1 I I I 1 t SH23 5.25 J_l 1 1 1 I 1 I SH41 6.50 SITE i i i i i i i i i i i i i i l i i , \ , • 11 , . \ 1 I , , ,. 1 0 40ho- HO* W GRADE Figure 13.2.2 Histograms of Laminar Base Angles (Vert Scales : 1 individual = 2 mm.) 284 EXPOSURE MEAN LAMINA STANDARD SITE GRADE BASE ANGLE * ERROR MCI 4.75 165.78 1.75 MG6 4.50 140.04 8.09 MG7 3.50 92.94 3.53 MG8 2.00 58.40 2.83 MG9 1.75 52.88 2.21 SH21 6.00 264.20 3.44 SH22 1.50 44.62 2.16 SH23 5.25 226.60 9.73 SH24 4.50 212.39 8.72 SH41 6.50 222.75 11.73 OP 67 2.50 110.21 5.39 0P68 3.50 120.45 4.38 0P69 4.25 144.55 4.87 0P70 3.75 139.17 5.81 Table 13.3.1 Exposure Grades and Mean Laralnaria digitata Lamina Base Angles for Selected Sites 285 Mean Lamina Base Angle 250 200 150 100 50 Limit of occurrence of Laminaria digitata at abundance of "occasional" or more. 2 3 4 5 6 7 8 Exposure Grade Figure 13»3»3 Mean Lamina Base Angle vs. Exposure Grade 286 any small amount of wave action at low water would make the researcher or the plants move. About 30 adult plants were taken from each site in a random manner. Young plants were not selected because they always had a small lamina base angle. In the laboratory, each plant was flattened on to a table, and the angle of the lamina base was measured at a radius of 10 cm. from the stipe end using a large protractor. The flattening process meant that angles in excess of 360° were possible with overlapping of the two sides of the lamina. Histograms of the lamina base angles at the various sites are shown in Figure 13.3.2, while the means and standard errors are given in Table 13.3.1. Mean lamina base angle and exposure grade are plotted in Figure 13.3.3. The two variables are highly correlated (r = 0.937 which is highly significant or p < 0.001 with 12 degrees of freedom), and the relationship may be described by the following linear regression: Y = -20.9 + 42.2 X where Y is the lamina base angle and X is exposure grade. Since the lamina base angle in this case must be related to the amount of wave action, the linearity of the relationship between lamina base angle and exposure grade is further proof of the reliability of the exposure scale. Assuming that the biological exposure scale is approximately inverse in relation to wave action, it follows that the morphological response of L. digitata occurs in a similar inverse manner. 13.4 Fucus vesiculosus Burrows and Lodge (1951) commented on the variation in vesiculation of Fuous Vesioulosus depending on the location of the site in relation to exposure to wave action. As shown in Figure 2.3.6 and Fiche 2, 287 F, vesiculosus occurs in Shetland in reasonable quantities at sites in the exposure range Grade 4.00 to Grade 9.00. As the location becomes more exposed, fewer vesicles are observed on smaller plants. At locations more exposed than Grade 4.00, vesicles are absent from F. vesiculosus and the plant is known as F. vesiculosus f. linearis. This form occurs over a narrow range of exposure from Grade 1.50 to Grade 3.75. Boney (1966) points out that vesiculation is a seasonal process and appears to depend upon photosynthetic activity. Most vesicles are formed over the months of March and April, but occasional vesicles may be added as late as June or July (Knight and Parke, 1950). From the juvenile stages, Knight and Parke found that vesiculation starts in the following spring after the plant has reached a length of 10 - 14 cm. As the plant continues to increase in size, more vesicles are added particularly in each spring over the typical life span of 3 - 5 years. It is clear that the number of vesicles is related to plant size, and that a study of vesiculation in relation to wave exposure must include a measure of plant size as well as a count of vesicles. The fresh weight of the plant was chosen as the easiest measure of size. Ten plants were sampled from three shoreline sites in Shetland. These were: Clubb of Mulla (SH40, Grade 4.75), Aith Voe (SH37, Grade 7.00) and Clousta (SH34, Grade 8.25). Plants were selected at random from the middle of the zone of maximum abundance since Knight and Parke (1950) state that there are usually less vesicles on similar sized plants further up the zone. In the laboratory, the plants were shaken to remove surface water and littorinids before being weighed. The vesicles on each plant were then counted (Table 13.4.1). 288 Clubb of Mulla - E. G. 4.75 Fucus vesiculosus Fresh Weight No. Vesicles (g) 79.26 124 24.53 30 113.24 187 25.75 65 140.75 203 6.58 9 27.62 51 78.58 134 33.92 21 113.33 183 Aith Voe - E.G. 7.00 Fucus vesiculosus Fresh Weight No. Vesicles (s) 164.28 381 20.05 46 69.70 315 75.07 178 73.15 167 38.09 93 54.75 131 44.12 64 48.28 93 69.99 156 Clousta - E.G. 8.25 Fucus vesiculosus Fresh Weight No. Vesicles (g) 115.18 545 14.43 47 48.82 182 160.22 479 26.85 125 78.74 311 200.60 582 206.62 464 31.30 113 40.56 120 Table 13.4.1 Fresh Weight and No. Vesicles on Fucus vesiculosus Plants from Selected Locations 289 Figure 13.4.1 shows the number of vesicles on each plant plotted against its fresh weight, with linear regressions put through the points. With normal linear regressions, the value of the intercept was very small for the samples from Clubb of Mulla and Aith Voe (0.840 and 2.170 respectively), while the intercept was a high positive value (62.1) for the sample from Clousta. Since there was no possibility of 62 bladders with no fresh weight, the regression lines of samples from all the sites were forced through the origin for comparison. The regressions were as follows : Clubb of Mulla Y = 1.56 X Aith Voe Y = 2.46 X Clousta Y = 2.97 X where Y is the number of vesicles and X is fresh weight of the plant. In order to test whether the regressions were significantly different from each other, a t test as described by Bailey (1959) was used as follows: bl - b2 = I 1 1 z S Jzi(x-x1)^ + Z2(x-x2) I S 2 + S where S = / 1 2 2 Clubb of Mulla/Aith Voe : t = 19.438 n = 10 d.f. = 8 Aith Voe/Clousta : t = 8.333 n = 10 d.f. = 8 From tables, for d.f. = 8, t = 5.041 at p = 0.001. It can be seen that the regression lines are significantly different at a probability of 0.1%, As an insect to Figure 13.4.1, the slopes of the regression lines have been plotted against exposure grade. For the three sites from which samples were taken, it seems that the relationship between exposure grade and this morphological change in Fuous vesioutosus is linear. This follows the pattern set by the lamina base angle of Laminavia dzgi-tata^ and further demonstrates the fact that the exposure scale and changes in species morphology are related to wave action in a similar way. 100 200 g. Fresh Weight of Plant Clousta Aith Voe Clubb of Mu11a Figure 13.4.1 No. Vesicles vs. Fresh Weight of Fucus vesiculosus in Relation to Exposure Grade. 291 CHAPTER 12 Height of Zones The zonation of animals and plants on rocky shores is mainly a result of varying degrees of tolerance to desiccation (Colman, 1933) . Species growing in the topshore region are more able to withstand desiccation than those growing further down the shore. On exposed shores, swash and spray from waves reach further up the shore, and consequently the zonation of species is extended and uplifted in comparison to more sheltered areas. Burrows et al (1954) have studied this process in the comparison of an exposed and sheltered shore in Fair Isle. The top height of certain plant and animal zones above a fixed datum has been used by Jones (1959) and Jones and Demetropoulos (1968) as a measure of the relative wave exposure of shore. Dalby et al (1978) concentrated on the top height of the "black lichen zone" as an indicator of the relative exposure of shores in the Fensfjord area of Norway. This was a useful group of species to use because it was ubiquitous throughout the exposure range and it was also readily visible. The reciprocal of the exposure grade of the shore was related to the top height of the "black lichen zone" and a linear relation was found. A similar relationship was sought for the Shetland Islands. The top height of the "black lichen zone" above chart datum was recorded from sites MG1 - SH43. Where possible, this parameter was extracted from the data sheets supplied by OPRU for sites OP44 - 0P83. The values from 67 sites were obtained (Table 14.0.1) and used in finding the relationship shown in Figure 14.0.1. Where exposure grade is plotted against black lichen height it can be seen that the latter stays at a value of under 4.00 m. until shores become more exposed (smaller grades) than about Grade 2.50. Presumably this is the point where the waves 292 BUCK LICHEN HEIGHT BLACK LICHEN SITE GRADE m. above C.D. SITE GRADE HEIGHT m« a We CI MG1 4.75 3.6 SH35 7.75 2.4 MG2 5.75 3.0 SH36 5.25 3.0 MG3 7.50 2.7 SH37 7.00 2.9 MG4 7.50 2.9 SH38 7.75 2.8 MG5 7.50 2.5 SH39 7.75 2.8 MG6 4.50 3.8 SH40 4.75 3.0 MG7 3.50 ? SH41 6.50 2.6 MG8 2.00 5.0 SH42 2.50 5.2 MG9 1.75 10.9 SH43 1.75 7.9 MG10 0.50 15.4 0P44 4.50 3.9 MG11 0.00 27.5 0P45 2.50 3.6 SH12 5.75 2.7 0P47 3.75 3.4 SH13 2.00 5.0 OP 49 1.50 6.6 SH14 0.00 25.5 OP52 3.00 4.1 SH15 0.50 10.5 OP56 7.75 2.0 SHI 6 1.75 8.3 0P57 6.75 2.8 SH17 6.00 3.2 0P59 5.75 2.5 SH18 7.75 2.5 0P60 7.50 2.9 SH19 1.00 6.5 0P61 7.00 2.5 SH20 2.75 3.2 0P62 5.00 4.1 SH21 6.00 3.1 OP 63 4.50 3.5 SH22 1.50 7.4 0P64 4.25 3.7 SH23 5.25 3.4 0P66 4.50 4.2 SH24 4.50 4.5 0P68 3.50 4.0 SH25 8.50 2.0 OP69 4.25 3.4 SH26 5.00 2.4 0P71 3.00 4.1 SH27 2.75 3.9 0P72 3.25 4.1 SH28 0.00 32.4 0P73 1.75 5.3 SH29 3.00 2.9 0P74 3.00 3.7 SH30 0.00 18.4 0P75 5.75 3.1 SH31 9.00 2.6 0P76 3.75 2.9 SH32 9.00 2.4 0P77 2.50 3.8 SH33 8.25 2.4 0P79 3.00 5.0 SH34 8.25 2.8 0P82 2.50 3.7 ? - top of transect influenced by splash zone of more exposed site Table 14.0.1 Exposure Grades and Slack Lichen Heights • a aa £KX3 D rot o a a —r« V.OO 12.00 16.00 20.00 24.00 32.00 BLACK LICHEN HIEGHT 12.00 18.00 20.00 24.00 28.00 32.00 3S.0Q BLACK LICHEN HrEGHt Figure 14.0.1 Black Lichen Height y8. Expoaure Grade HI 294 are usually large enough to produce a significant amount of spray on breaking. The top height of the black lichen zone becomes much higher on shores more exposed than Grade 2.50 as the spray reaches further up the cliff. Figure 14.0.1 also shows that a linear regression can be fitted through the points if the reciprocal of the exposure grade is plotted against black lichen height. The regression equation formed in this way is different to that produced by Dalby et al (1978) for the Fensfjord area of Norway because unity had to be added to the Shetland exposure grades to allow Grade 0 shores to be included. The regression equations are: Norway : 1/E = -0.0123 + 0.0911 H Shetland : 1/(E+1) = 0.0733 + 0.0357 H where E is exposure grade and H is black lichen height. However, the relationship between black lichen height and exposure grade is remarkably similar for the two areas as demonstrated by calculating expected black lichen heights from the regression equations. For example, a Grade 1 shore in Norway should have a black lichen height of 11.11 m. whereas a shore of the same grade in Shetland should have a black lichen height of 11.94 m. This indicates that the exposure scales for Norway and Shetland are directly compatable in terms of wave exposure, and that the inclusion of Grade 0 shores for Shetland was justified as shown by the black lichen heights for these shores. It appears that the relationship between black lichen height and exposure grade is of the inverse type. This might be expected since black lichen height is the same as the dominant spray height from wave action. Other physical measurements of wave action (Part III) have also indicated that the relationship between wave action and exposure grade is approximately inverse. Morphological characteristics of species are, however, related to exposure grade in a linear fashion since they both represent a biological response to wave action. PART V SUMMARY 295 The Usefulness of the Biological Exposure Scale As a quick method of estimating wave exposure, the biological exposure scale concept has some unique advantages. Assuming wave action to be the primary influence on rocky shore ecology, the use of species abundances to indicate wave exposure means that the exposure status of the shore has been categorised over the life-time of the plants and animals present. In the case of natural shorelines, the wave climate over at least the preceeding three years has been accounted for. The estimate of wave exposure using the biological scale can also be produced instantly, without the time-consuming installation of costly equipment. However, the use of biological indicators has an obvious disadvantage in that the distribution and abundance of species changes, with geographical location. Thus it was not possible to apply a scale that had been developed in Norway to the Shetland Islands, and a new scale had to be formed for the latter lpcation. The formation of a biological exposure scale initially has a subjective component when shoreline sites are put in to whole unit grades of exposure. The subjectivity of this process was reduced by a number of aids, par- ticularly ordination methods in which the primary axis of variation was clearly related to wave exposure. It was appreciated that the grades of exposure were not necessarily regularly placed along the scale, although subsequent measurements of wave action and morphological characteristics of species indicated that the grades are indeed regularly placed on an inverse scale. Any gross error in the placing of a particular site on the scale was removed by an averaging and smoothing process that was applied to all the sites in the formation of the final scale. Two cycles of the process were used in the preparation of the exposure scale to obtain a "precision" of J exposure grade unit. Sucsequently the effect of using more cycles was investigated. The exposure grade estimates were not 2 96 improved, and it was decided that two cycles were sufficient. Use of the exposure scale involves a completely objective technique whereby the species maximum abundance scores from any new sites are compared with the standard abundance scores comprising the scale. The exposure grades of new sites in Shetland are in accordance with what would be expected, and indeed, the exposure scale has been shown to respond sensitively to changes in wave exposure over short distances. It was also shown to be a very robust technique because a change in the abundance measurement method and the selection of different vertical intervals on the shore did not greatly influence the exposure grade that was assigned to a shore. The biological exposure scale is based on the assumption that differences in ecology between sites over a limited geographical area are related primarily to wave action. It was appreciated that some species show greater changes in abundance over the exposure gradient than others, and initially 31 species were used in the assessment of exposure grade. The omission of all the animals or all the plants led to a deterioration in the exposure grade estimates, but a balanced reduction in the number of species used actually seemed to produce a better estimate of wave exposure for many sites as the influence of species responding to other environmental variables was removed. It was found that reliable exposure grade estimates could be produced using only 19 "strong species". The influence of environmental variables other than wave action on exposure grade was tested using a variety of statistical techniques. Measured or estimated environmental variables were divided into exposure factors and secondary physical factors. Three of the former were used to calculate expected exposure grade using a multiple regression. By plotting the difference between observed and expected exposure grade against the secondary physical factors, the variables relating to the particularity of the substrate were found to have a considerable influenc on the observed exposure grade. It was concluded that shores with a highly particulate substrate could not be assigned reliably to exposure grades because the mobility of the substrate caused a reduction in species1 abundances. The slope of the shore was also found to exert an influence on exposure grade in that a steep shore seemed more exposed than expected from the likely wave environment of the area. It seemed that the exposure scale could be confidently applied to a wide range of rocky shore situations in Shetland. Exposure grades assigned to these sites were not found to change greatly with season or from year to year, and this further supported the reliability of the exposure grading technique. The Exposure Scale Related to Wave Action More information was required on the physical basis of the scale such that it could be "calibrated" in terms of a measurement of wave action. This would give an idea of the spacing of grades on the scale, and would also allow scales formed for different geographical areas to be compared. Wave impact pressures were measured at a number of shoreLine sites in Shetland covering the exposure grade range from Grade 1.75 to Grade 7.75. The sensors were flush diaphragm silicon semiconductor strain guages mounted parallel to the rock surface at mid-tide level. They were connected to the recording instruments which consisted of a signal conditioning module and a light beam chart recorder. Wave pressure measurements were taken as the waves impacted against the transducer at mid-tide. Although a wide range of wave conditions were experienced, 298 it was noted that the impact pressures were never very large, and usually not much greater than the hydrostatic pressure due to the weight of water in the wave. Short duration shock pressures were frequently encountered, usually at the beginning of the wave impulse, but these were also of a similar order of magnitude. At two of the sites on two separate occasions, four sensors were located in different positions at the same tidal level. Differences in the wave forms were explicable, but again, the overall magnitude of the wave pressures were similar. For example, slightly larger shock pressures were more frequently encountered from sensors mounted on a vertical rock face, but no very large shock pressures were encountered. It was concluded that these must be very rare on natural rocky shores. The largest- shock pressure measured was 4.55 PSI from a dominant wave height of 3.20 m. Much information was obtained from four sensors located around an exposed headland where the exposure grades ranged from Grade 1.75 to Grade 4.50. The area was dominated by swell from the Atlantic Ocean, and there was continuous water movement at the sites. Since simultaneous measurements of wave pressures had been obtained, it was possible to compare the significant wave pressures on each day of recording. In this way, a family of curves was obtained relating significant wave pressure to the exposure grade of each of the sites. The curves were inverse in form, thereby indicating that the grades on the exposure scale are approximately inversely spaced in relation to wave action. Wave pressure measurements were also taken from sites influenced only by locally wind-driven waves. Waves were only produced when the wind was from the appropriate direction, and for long periods the sea at these sites was calm. When waves were produced, more shock pressures were encountered than at sites dominated by swell, but the magnitude of these pressures was still similar to the hydrostatic wave pressure. 299 In order to compare wave pressures from these sites with those from the sites dominated by swell, extrapolation of the wave pressure data was attempted by relating measured wave pressures to longer term records of wind speed and wave height. Unfortunately, the relationships between the variables were not significant enough for predicting wave pressures, and extrapolation was not possible. However, it was possible to state that representative wave pressures had been measured from the various sites. The low magnitude of the wave pressures recorded, and the different types of wave action observed at sites dominated by swell and local wind-driven waves, led to the formation of a hypothesis about the way in which wave action influences the ecology of the shore. The most vulnerable stage in the life-cycle of littoral species must be in their planktonic stage when the plant spores and the animal larvae become attached to the shore. At this time, drag forces caused by water movement are likely to be more important than actual impact pressures in preventing the attachment of the juvenile forms. Sites dominated by swell have continuous water movement which must make the attachment of spores and larvae very difficult in comparison to their ease of establishment in calm periods on shores dominated by the occasional wind-driven waves. In this way, the frequency of wave action would be important. The relative magnitude of drag forces between sites would probably contribute to the selective reduction of different species throughout their life- span to produce the characteristic communities on exposed and sheltered shores. Species such as Nuoella lapiHus, which do not have a planktonic dispersal phase, would be less influenced by continuous water movement in their juvenile stages. This may explain the occurrence of a diversity of shell shape forms in Shetland on all sites except the most exposed where the magnitude rather than the frequency of drag forces would be sufficient to exert a selection pressure. Further support for the hypothesis comes from vertical rock surfaces which biologically appear to be very exposed although they rarely receive large impacts because they produce standing waves or claposis. However, these vertical rock surfaces do cause much water movement and difficulty for the attach- ment of spores and larvae. In order to prove the general hypothesis, research into the relative ease of settlement of different species under different laboratory conditions would be required. If the hypothesis is true, and drag forces are found to be of major importance in determining species distribution and abundance, the wave impact pressures described in this theses would still be valid since the drag forces would be related to the impact pressures. Measurements were taken of the top height of the "black lichen zone" from 67 of the sites that were studied in Shetland. The relation- ship between black lichen height and exposure grade was found to be inverse in form. In accordance with the significant wave pressure and exposure grade relationship, this was to be expected since the black lichen height was a direct measure of the height of spray caused by the intensity of wave action. Comparison with a similar relationship for Norway showed that the same grades on the scales developed for the two regions represented similar conditions. Finally, measurements of various morphological characteristics of species over the exposure range showed that the morphology of these species is related to exposure grade in a linear fashion. This is to be expected, since both variables are express- ions of a biological response to wave action. In conclusion, it must be stressed that although the biological exposure scale has been shown to be a reliable means of estimating a com- ponent of wave exposure, the conclusions drawn in the present study may not 301 be equally valid if extended beyond the study area. Biologically more exposed shores are known from Shetland than those examined at Mavis Grind, and published records of wave action in Shetland and elsewhere amply confirm that in conditions of high sea and swell, wave impact pressures may attain exceedingly high values. Such extreme wave press- ure environments are probably not reflected differentially in species composition, so the biological exposure grade 0 must cover a great range of wave impact pressures, far beyond those encountered at Mavis Grind. On shores of low to moderate wave height the wave impact pressure as measured here, appears to be mainly a combination of frequency and overall magnitude of the drag forces, and it is likely that it is this component of wave action which is assessed by the biological exposure scale. By relating species characteristics to exposure grade, it seems that the exposure scale of Norway is numerically comparable to that for Shetland, and the exposure grades are regularly spaced on a wave exposure scale. Measurements of wave pressures indicate that the biological scale (numbered from 0 for exposure, to 9 for shelter) is an inverse expression of wave exposure and is probably related in some exponential manner. 302 ACKNOWLEDGEMENTS I would like to thank Dr. D.H. Dalby of the Botany Department, Imperial College, for his advice and guidance throughout his supervision of the project. It was most generaously funded by the Environmental Control Centre of British Petroleum, and my thanks are also due to Dr. W.J. Syratt and Dr. D.C. Monk of BP who assisted me in the field in Shetland. I would al so like to thank the staff of the Oil Pollution Research Unit of the Field Studies Council who have provided me with a large amount of biological data from shoreline sites. The data was collected for the Shetland Oil Terminal Environmental Advisory Group, and I gratefully acknowledge their permission to use it. Other people also provided very useful data for which I am grateful: J.A. Fowler and his team from the School of Life Sciences, Leicester Polytechnic, who provided biological data from sites on Yell, Shetland; the staff of the Lerwick Observatory for meteorological data; Mr. S. Milligan of Weisdale together with the Shetland Islands Council for wave height data from Yell Sound; Mr. M. Birkinshaw of BP and Mr. T. Pitt of the Institute of Oceanographic Sciences for wave height data from Fitzroy. I am also grateful for the considerable advice given by Mr. J. Neale of the Civil Engineering Department, Imperial College, in the selection and operation of the wave pressure measuring equipment. Thanks are also due to Dr. M. Baker of the same department, who lent equipment and pro- vided testing facilities at the college. Similarly, thanks are due to Dr. P. Bearman of the Aeronautics Department, Imperial College, who provided testing facilities for the anemometer. I would also- like to express my gratitude to Mr. T. Cottam of Kulite Sensors Ltd., Basingstoke, and Mr. F. Williamson of Bell and Howell Ltd., Basingstoke. Thanks are also due to Dr. R. Dockworth of BP for providing the wave staff, and 303 Mr. J. Whittick of the Botany Department, Imperial College, for building the hut and making other components used in the study. I am also grateful for computing assistance given by Dr. P. Mueller (Botany Department), Dr. A. Morton (Botany Department) and Dr. A. Ludlow (Zoology Department) of Imperial College. Extensive use was made of the computing facilities offered by the Imperial College Computing Centre. Finally, I would like to thank the staff of the Pollution Control Centre at the Oil Terminal in Shetland who helped me a great deal in transporting equipment to the study area. I would also like to express my gratitude to Mr. A. Doull of Isleburgh, Brae, Shetland who allowed me to have access to his land and install equipment on it. 304 REFERENCES ADMIRALTY HYDROGRAPHIC DEPARTMENT (1980). Tide Tables. Vol. 1. European Waters. ALLEN, S.E. et al (1974). Chemical Analysis of Ecological Materials. Blackwell, Oxford. 565 pp. BAGNOLD, R.A. (1939). Interim report on wave pressure research. J. Inst. Civ. Eng. 12,: 202-226. BAILEY, N.T.J. (1959). Statistical Methods in Biology. English Universities Press. 198 pp. BAKER, J.M. (1976a). Biological monitoring - principles, methods, difficulties. In Marine Ecology and Oil Pollution, (ed. Baker, J.M.) Applied Science Publishers, Barking, Essex. 566 pp. BAKER, J.M. (1976b). Ecological changes in Milford Haven during its history as an oil port. In Marine Ecology and Oil Pollution. (ed. Baker, J.M.) Applied Science, Barking, Essex. 566 pp. BAKER, J.M. et al (1976). Biological surveys of rocky shores in the region of Sullom Voe, Shetland. May 1976. Field Studies Council, Oil Pollution Research Unit. BAKER, J.M. et al (1977). A resurvey of rocky shore transects in the region of Sullom Voe, Shetland. May 1977. Field Studies Council, Oil Pollution Research Unit. BALLANTINE, W.J. (1961). A biologically defined exposure scale for the comparative description of rocky shores. Field Studies 1(3): 1-19. BELL & HOWELL LTD. (n.d.). BHL 5000 Minigraph Operation and Maintenance Manual. BELL & HOWELL LTD. (n.d.). BHL 5107 Manual. BERRY, R.J. (1974). The Shetland fauna, its significance or lack thereof. In The Natural Environment of Shetland. (ed. Goodier, R.) Nature Conservancy Council, Edinburgh. 178 pp. BOALCH, G.T. (1957). Marine algal zonation and substratum in Beer Bay, South East Devon. J. Mar. Biol. U.K. 36: 519-528. BONEY, A.D. (1966). A Biology of Marine Algae. Hutchinson Educational, London. 216 pp. BORGESEN, F. (1903). The marine algae of the Shetlands. J. Bot. Lond. 41_: 300-306. BURROWS, E.M. & LODGE, S. (1951) . Autecology and the species problem in Fucus. JMBA 30i: 161-176. BURROWS, E.M., CONWAY, E., LODGE, S.M. & POWELL, H.T. (1954). The raising of intertidal algal zones on Fair Isle. J. Eool. kly 283-288. COASTAL ENGINEERING (1960). Proceedings of 7th Conference on Coastal Engineering. The Hague, August 1960. 2 vols. Council on Wave Research, The Engineering Foundation. 1001 pp. COASTAL ENGINEERING (1974). Proceedings of 14th Conference on Coastal Engineering. Copenhagen, June 1974. 4 vols. American Society of Civil Engineers. 2650 pp. COLMAN, J. (1933). Nature of intertidal zonation of plants and animals. J. Mar. Biol. Ass. U.K. 18_i 435-476. CRISP, D.J. & SOUTHWARD, A.J. (1958). The distribution of intertidal organisms along the coasts of the English Channel. J. Mar. Biol. Ass. U.K. 37_: 157-208. CROTHERS, J.H. (1973). On variation in Nucella lapillus: shell shape in populations from Pembrokeshire, South Wales. Proc. Malach Soc. Lond. 40: 319-327. CROTHERS, J.H. (1974). On variation in Nucella lapillusi shell shape in populations from the Bristol Channel. Proc. Malach Soc, Lond. 41_: 157-170. CROTHERS, J.H. (1975a). On variation in Nucella lapillusi shell shape in populations from the Bristol Channel. Proc. Malach Soc. Lond. 41: 489-498. CROTHERS, J.H. (1975b). On variation in Nucella lapillusi shell shape in populations from the Channel Islands and North-West France. Proc. Malach Soc. Lond. 4U 499-502. CROTHERS, J.H. (1977). On variation in Nucella lapillusi shell shape in populations towards the Southern limit of its European Range. J. Molluscan Studies 43_: 181-188. CROTHERS, J.H. (1979). Variation in the shell of the dog-welck, Nuoella lapillus from Sullom Voe and other parts of the Shetland Islands Marine Environ. Res. 311-327. DALBY, D.H., COWELL, E.B. & SYRATT, W.J. (1978). Biological monitoring around an oil refinery. In Monitoring the Marine Environment. Sept. 1978. Institute of Biology, London DALBY, D.H., COWELL, E.B., SYRATT, W.J. & CROTHERS, J.H. (1978). An exposure scale for marine shores in Western Norway. J. Mar. Biol. Ass. U.K. 58: 975-996. DARBYSHIRE, M. & DRAPER, L. (1963). Forecasting wind generated sea waves. Engineering 195: 482-484. DAVIES, (1971). Computer Programming in Quantitative Biology. Academic Press, London. 492 pp. DEFANT, A. (1961). Physical Oceanography Vol. II. Pergamon Press, Oxford. 598 pp. DENNY, D.F. (1951). Further experiments on wave pressures. J. Inst. Civ. Eng. 35: 330-345. DIXON, P.S. (1963). Marine algae of Shetland. Br. Phycol. Bull, ly 236-244. DRAPER, L. (1967). The analysis and presentation of wave data - a plea for uniformity. Proc. 10th Conf. on Coastal Engineering Vol. I. pp. 1-11. DRAPER, L. & SQUIRE, E. (1967). Waves at ocean weather ship station India 59N 19W. Roy. Inst. Naval Architects Trans. 109: 85-93. EVANS, R.G. (1947a). The intertidal ecology of selected localities in the Plymouth neighbourhood. J. Mar. Biol. Ass. U.K. 27: 173-218. EVANS, R.G. (1947b). The intertidal ecology of Cardigan Bay. J. Ecol. 34: 273-309. FLINN, D. (1974). The coastline of Shetland. In The Natural Environment of Shetland. (ed. Goodier, R.) The Nature Conservancy Council Edinburgh. FOWLER, J.A. (1978). Ecological studies in the maritime approaches to the Shetland oil terminal. Leicester Polytechnic School of Life Sciences. FUHRBOTEN, A. (1970). Air entrainment and energy dissipation in breakers In Proc. 12th Coastal Engineering Conf. Vol. 1. Sept. 1970. Washington D.C. GAILLARD, D.D. (1904). Wave action in relation to engineering structures U.S. Army Corps of Engineers. GIBB, D.C. (1957). The free living forms of Ascophyllum nodosum. J. Ecol. 45: 49-83. GOLDSMITH, 0. (1859). A History of the Earth and Animated Nature. Vol. 1. Blackie, London. 564 pp. GUILER, E.R. (1949). The intertidal ecology of Tasmania. Pap. & Proc. Roy. Soc. Tasm. 1949 135-200. HANDBOOK OF OCEANOGRAPHIC TABLES (1966). Instruments. U.S. Naval Ocean- ographic Office, Washington D.C. HELLER, J. (1975). The taxonomy of some British Littorina species, with notes on their reproduction. Zool. J. Linn. Soc. 56: 131-151. HILL, M.O. (1973). Reciprocal averaging: an eigen vector method of ordination. J. Eaol. 61^: 237-249. HIROI, I. (1920). The force and power of waves. Engineer 184-185. HISCOCK, K. et al (1978). A resurvey of rocky shore transects in the region of Sullom Voe, Shetland. May 1978. Field Studies Council, Oil Pollution Research Unit. HISCOCK, K. et al (1979). A resurvey of rocky shore transects in the region of Sullom Voe, Shetland. May 1979. Field Studies Council, Oil Pollution Research Unit. HORNE, R.A. (1969). Marine Chemistry. Wiley-Interscience, London. 568 pp. HYDRAULICS RESEARCH STATION (1976). Orka Voe, Shetland Isles. Wave Refraction Studies. Report No. EX 724. INSTITUTE OF TERRESTRIAL ECOLOGY (1977). Report to NCC on some aspects of the ecology of Shetland. IRVINE, D.E.G. (1974). The marine vegetation of the Shetland Isles. In The Natural Environment of Shetland. (ed. Goodier, R.) Nature Conservancy Council, Edinburgh. 178 pp. JAMES, B.L. (1968). The distribution and keys of species in the family Littorinidae and of their digenean parasites, in the region of Dale, Pembrokeshire. Field Studies 2(5)i 615-649. JAMES, P.W. (1965). A new check-list of British lichens. Liohenologist 3: 95-135. JOHNSON, D.W. (1919). Shore Processes and Shoreline Development. Hafner, London, pp. 55-86. JONES, W.E. (1959). The effects of exposure on the zonation of algae on Bardsey Island. Rep. Bardsey Bird Fid. Obs. 7j 41-46. JONES, W.E. (1974). Changes in the seaweed flora of the British Isles. In The Changing Flora and Fauna of Britain, (ed. Hawksworth, D.L.) Academic Press, London. 97-113. JONES, W.E. & DEMETROPOULOS, A. (1968). Exposure to wave action: measure- ment of an important ecological parameter on rocky shores in Anglesey. J. Exp. Mar. Biol. Eaol. 2_: 46-63. JONES, W.E. et al (1978). Intertidal surveillance. In Monitoring the Marine Environment. Sept. 1978. Institute of Biology, London. JONES, W.E., BENNELL, S.J., McCONNELL, B.J. & SMITH, S. (1980). The sixth report of the coastal surveillance unit. Department of Marine Biology, University College of North Wales. 43 pp. KAIN, J.M. (1976). New and interesting marine algae from the Shetland Isles. II. Hollow and solid stiped Laminaria. Br. Phyool. J. U: 1-11. KAMEL, A. (1971). Wave pressure on seawalls and breakwaters. Bull, of the Permanent Int. 4ss. of Navigation Congresses _2(8): 63-83. KITCHING, J.A. (1934) . An introduction to the ecology of intertidal rock surfaces on the coast of Argyll. Trans. Roy. Soo. Edin. 58(2): 351-374. 311 KNIGHT, M. & PARKE, M. (1950). A biological study of Fuous Vesiculosis and Fuous serratus. J. Mar. Biol. Ass. U.K. 29_: 439-514. KULITE SEMICONDUCTOR INC. (n.d.). Strain Gauges. Bulletin KSG-SC. 19 pp. LEWIS, J.R. (1964). The Ecology of Rocky Shores. Hodder and Stoughton, London. 323 pp. LEWIS, J.R. (1976). Long-term ecological surveillance: practical realities in the rocky littoral. Oceanogr. Mar. Biol. Ann. Rev. 14: 371-390. LYSAGHT, A.M. (1941). The biology and trematode parasites of the Gastropod Littorina neritoides on the Plymouth breakwater. J. Mar. Biol. Ass. U.K. 25: 41-80. MARINE BIOLOGICAL ASSOCIATION (1957). Plymouth Marine Fauna. 3rd ed. Plymouth. 457 pp. MARSHALL, E. (1978). Shetland*s Oil Era. Phase 2. Shetland Islands Council. 107 pp. MILLER, R.L. et al (1974a). Field measurements of impact pressures in surf. Proceedings of 14th Coastal Engineering Conference3 Copenhagen. June 1974. Vol. III. 1761-1777. MILLER, R.L. et al (1974b). The effect of breaker shape on impact pressures in surf. Tech. Rep. No. 14. Fluid Dynamics & Sediment Transport Lab., University of Chicago. September 1974. MOLITOR, D.A. (1935). Wave pressures on sea walls and breakwaters. Trans. Am. Soc. Civ. Eng. 100: 984-1002. MONK, D.C., COWELL, E.B. & SYRATT, W.J. (1978). The littoral ecology of the area around Mongstad Refinery, Fensfjorden, during the three years after refinery commissioning, 1975-1977. B.P., London. MOORE, H.B. (1935). The biology of Balanus balanoides. IV. Relation to environmental factors. J. Mar. Biol. dss. U.K. 20: 279-307. MOYSE, J. & NELSON-SMITH, A. (1963). Zonation of animals and plants on rocky shores around Dale, Pembrokeshire. Field Studies Ij 1-31. MYERS, A.A., CROSS, T.F. & SOUTHGATE, T. (1978). Bantry Bay survey. First Annual Report, Dept. of Zoology, University College.; Cork. NELSON-SMITH, A. (1970). Techniques: surveying rocky shores. Fieldworker I: 50-52. ORLOV, L. (1966). Geometric models in ecology. I. The theory and application of some ordination methods. J. Eool. 54: 193-215. PARKE, M. & DIXON, P.S. (1976). Check-list of British marine algae. J. Mar. Biol. Ass. U.K. 56: 527-594. POWELL, H.T. (1963a). Speciation in the genus Fuous L. and related genera. In Speciation in the Sea. (ed. Harding, J.P. & Tebble, N.) Systematics Assoc. Pub. No. 5, London. 199 pp. POWELL, H.T. (1963b). new records of Fucus distichus subspecies for the Shetland and Orkney Islands. Br. Phycol. Bull. 2i 247.254. REES, T.K. (1935). Marine algae of Lough Ine. J. Ecol. 23: 69-133. de ROUVILLE, A., BESSON, P. & PETRY, P. (1938). Etat actuel des etudes Internationales sur les efforts dus aux lames. Ann. Fonts et Chaussees 108(2): 4-113. RUSSELL, R.C.H. & MACMILLAN, D.H. (1952). Waves and Tides. Hutchinson, London. 348 pp. SAETRE, H.J. (1974). On high wave conditions in the northern North sea. IOS Report No. 3. SHELLARD, H.C. & DRAPER, L. (1975). Wind and wave relationships in U.K. coastal waters. Est. & Coastal Mar. Soi. _3: 219-228. SHETLAND ISLANDS COUNCIL (1978). Shetland in statistics No. 7. May 1978. SOUTHWARD, A.J. (1953). The ecology of some rocky shores in the south of the Isle of Man. Proc. Trans. L'pool Biol. Soc. 59_i 1-50. SOUTHWARD, A.J. & ORTON, J.H. (1954). Effects of wave action on the distribution and numbers of the commoner plants and animals living on the Plymouth breakwater. J. Mar. Biol. Ass. U.K. 33: 1-19. SOUTHWARD, A.J. & CRISP, D.J. (1956). Fluctuations in the distribution and abundance of intertidal barnacles. J. Mar. Biol. Ass. U.K. 35: 211-229. STEVENSON, T. (1849). Account of experiments upon the force of waves of the Atlantic and German Oceans. Trans. Roy. Soc. Edin. 16: 22-32. SYRATT, W.J. & COWELL, E.B. (1975). The littoral ecology of the area around Mongstad Refinery, Fensfjorden. Rafinor A/S & Co., Mongstad. SYRATT, W.J., MONK, D.C. & WRIGHT, R.A.D. (1980). The littoral ecology of the area around Mongstad Refinery, Fensfjorden. Routine Operational Survey 1979. British Petroleum for Rafinor A/S & Co., Mongstad. TANN, H.M. (1976). The estimation of wave parameters for the design of offshore structures. IOS Report No. 23. U.S. ARMY (1966). Shore protection, planning and design. U.S. Army Coastal Engineering Research Centre. Technical Report No. 4. WEIBULL, W. (1951). A statistical distribution of wide applicability. J. Applied Mech. 18,: 293-297. WIEGEL, R.L. (1956). Proa. 1st Conf. on Coastal Engineering Instruments3 Berkeley, California. Nov. 1955. Council on Wave Research, The Engineering Foundation. 302 pp. WINDOW, A.L. (1971). An Introduction to Strain Gauges. Welwyn Electric Ltd. APPENDICES APPENDIX 1 ABUNDANCE CATEGORIES Lichens Ex More than 80^ cover S 50 - 80^ cover A 20 - 49^ cover C 1 - 19^ cover F Large scattered patches 0 Widely scattered patches, all small R Only one or two patches Seaweed8 Ex More than cover S 60 - 89^ cover A 30 - 59^ cover C 5 - 29% cover F Less than 5"J* cover, zone still apparant 0 Scattered patches, zone indistinct R Only one or two plants BarnacleSt small "L. saxatalis" Ex More than 5 per sq cm S 3*5 per sq cm A 1-2 per sq cm C 11 - 100 per sq decimetre F 1-10 per sq decimetre, not more than 10 cm apart 0 1-10 per sq decimetre, few less than 10 cm apart R Less than 1 per sq metre Limpets and Winkles (except Littorinids above) Ex More than 200 per sq metre S 100 - 199 per sq metre A 50-99 per sq metre C 10-49 per sq metre F 1-9 per sq metre 0 1-9 per sq decametre R Less than 1 per sq decametre Gastropods (excluding Limpets and Winkles) Ex More than 100 per sq metre S 50-99 per sq metre A 10-49 per sq metre C 1-9 per sq metre, sometimes locally more F Less than 1 per sq metre, sometimes locally more 0 Always less than 1 per sq metre R- Less than 1 per sq, decametre Mussels Ex More than 80jC cover S 50 - 8 Each column represents a species numbered from 1 - 60 as follows: 1 Grimmia maritima 31 Codium fragile 2 Ramalina 32 Palmaria palmata 3 Grey green lichens 33 Corallina officinalis 4 Orange red lichens 34 Laurencia pinnatifida 5 Verrucaria maura 35 Laurencia hybrida 6 Verrucaria mucosa 36 Balanus balanoides 7 Lichina confinis 37 Littorina "saxatalis" 8 Hildenbrandia 38 Littorina littorea 9 Ulva lactuca 39 Littorina littoralis 10 Enteromorpha 40 Gibbula cineraria 11 Cladophora 41 Patella 12 Pelvetia canaliculata 42 Nucella lapillus 13 Fucus spiralis 43 Mytilus edulis 14 Fucus vesiculosus vesiculosus 44 Spirorbis 15 Fucus serratus 45 Pomatoceros 16 Himanthalia elongata 46 Halichondria 17 Ascophyllum nodosum 47 Actinia 18 Laminaria digitata 48 Fucus vesiculosus linearis 19 Laminaria saccharina 49 Fucus serratus free 20 Laminaria hyperborea 50 Bangia fuscopurpurea 21 Alaria esculenta 51 Scytosiphon lomentaria 22 Lithothamnia 52 Gelidium pusillum 23 Porphyra umbilicalis 53 Ectocarpus 24 Gigartina stellata 54 Spongomorpha 25 Chondrus crispus 55 Chorda filum 26 Catanella repens 56 Halydris siliquosa 27 Ceramiuin/Callithamnion 57 Porphyra linearis 28 Polysiphonia lanosa 58 Petalonia/Punctaria 29 Lomentaria articulata 59 Fucus distichus ancepa 30 Dumontia incrassata 60 Furcellaria fastigiata The maximum abundance scores are numerical equivalents of the abundance categories as followsi Ex 7; S 6; A 5; C 4; F 3; 0 2; R 1. Each row represents a transect, numbered as follows for each data sets MAXF78 - Max for MG sites in Feb 78 Row numbers correspond to MG site numbers MAXM78 - Max for 83 original sites in May 78 Row numbers correspond to MG, SH, and OP site numbers MAXA78 - Max for MG sites in Aug 78 Row numbers correspond to MG site numbers MAXN78 - Max for MG sites in Nov 78 Row numbers correspond to MG site numbers 3X8 MAXJ79 - Max for MG sites in June 79 1 MG1 11 MG7 CSU 21 MG9 CSU 2 MG2 12 MG7A OPRU 22 MG9 May 78 1m. 3 MG3 13 MG7A CSU 23 MG9 May 78 0.5 m. 4 MG4 14 MG7B OPRU 24 MG10 5 MG5 15 MG7B CSU 25 MG11 6 MG6 OPRU 16 MG8 OPRU 7 MG6 CSU 17 MG8 CSU 8 MG6A OPRU 18 MG8A OPRU 9 MG6A CSU 19 MG8A CSU 10 MG7 OPRU 20 MG9 OPRU MAXS79 - Max for MG sites and Leicester Polytechnic (LP) sites in Sep 79 1 MG1 11 MG7 2 MG2 12 MG8 3 MG2A 13 MG9 4 MG3 14 MG11 5 MG3A 15-29r Leicester Polytechnic 6 MG4 7 MG5 8 MG5A 9 MG5B 10 MG6 MAXM80 - Max for selected sites for March 1980 1 MG1 11 MG9 2 MG2 12 MG10 3 MG2A 13 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04447422223000240500264300300402340500006553000000100000010000000 3 0454751345500044070052350052030021350400722403000000000000000000 0 4 05557512243414440500453500303303453500547434030000000000000000000 5 00115502223213630500163420402300453402206343200 000300000020000000 6 01547501334411050500755400420400445401317433200000000000000000000 7 00246442262210440600053600202200532500307424040200000000000000000 8 0154652433353364040 0 0726 0 03 023 0 05322 0252752504 0000000000000000000 9 00015502254424550510053500343400553401507533030000003000000000000 10 01546440344101630105050610311300454304616334020000021000000000000 11 44547500142610200000032000200200220305106470000000000000000000000 12 01116523453324630520074500323200542205637303030000120000000000000 13 00001400052005702000000000020000000004503104000000000000000000000 14 06547604236423407400060300240000200403503023310000060000000000000 15 000023020202145050000402002o 0200200205633433220000004009000000000 16 to ON 327 APPENDIX 3 THE BIOLOGICAL EXPOSURE SCALE PRINT FROM PERMANENT FILE DATA 3 lst column is species no. as in Appendix 2. Then follows standard species abundance scores corresponding to ^ unit exposure grades from Grade 0 to Grade 9. CTi v0 OJ N v0 in COCO o o '•D O 00 N 00 CO N N VO rH VD CD VO COr H rH iH N in rH OJ •O N. CU rv CO h- OJ rt o N 0 V0 cr> IH m cu oj r—# fV 00 • a a a a • a a a a a a a a • • a a a a a a a a a a a . a a i—l rHt H OJ OJ ai -t Tf in CO CO '•Dv o m in rH rH TH rH rH OJ 01 0J 0J Ol tH O iH TH CO N vO 00 VO t—1 M) in 00 N iH OS * N CO IDNO OJ r-H tfi rv oj m m rH cu CO' 0 in OJ IS- 00 N CO CU CO CT\ CO vo in ch N CO CO f CO 1-1 OJ fV CO a a a a a a a • a a • • a a a a a a a a a a a a a a a • a a tH tH TH 01 cu CU tl- in 00 CO '•0 •-D *t in rH rH rH rH CO OJ 01 OJ OJ Ol tH •H f\. N o V0 OJ in "0 VO N CO OJ in rH N cu m Tf 0 N *h in oo rH 00 00 N OJ CO in Ol OJ CO vo CO OJ h- 00 h- ^ rH CO CO CO N m 00 00 m CO <3- CO V0 OS a a a a • a a a a a a a . . a a a a a a • a a a a • • a a a a TH rt iH OJ OJ cu rt in rt 00 CO VO W * rt m rH tH rH rH CO a\ oj ^ OJ OJ •h co oj m CO m in * OJ VD rH fj">C U ds VD CO K. CO o in OJ 0 in V0 cr. CO cr. OJ •0 O N 01 rt 0 v0 <0 as co t-l OJ CU rH V0 t-l OJ 00 Cfr vo m IT. o N OT 00 '•0 cr. iH V0 »H ON CO V0 in ^ a a a • a a a a a a a a a a a a a a a a a a a a a a a . a i—l rtrH 01 OJ OJ Tf in rf 00 CO 'D uo rt tf uo TH rH OJ rH CO it (\J i-l 01 CU cu ~ ^ <0 rH o rH 00 OJ rH O '•D ch 0 OJ CO & CO 0 N 0J 01 *h ^0 m rt Cn 0 N rt O CO OJ 0 v0 O 0J COCO VO V0 cr^ '•ON 0 V0 0 OJ V0 OS ru. v0 co cr> m oi • a a a a a a a a a a • a a a a a a a a a a a * .a a a a a 1-1 THr H 01 01 OJ Tf * in CO CO vO W in 01 in OJ iH rH 0J rH OJ rt OJ H 0J OJ OJ 1—t 0SO l OS rt o 00 o OJ CU o N y i CO CO ri- CO CU ^t in N OS m in »h n rH '.£1 0 N * O OJ CO CU os 1-1c h CO in 'D N OJ V0 0 rt in N N CO CO ^ Tf a a a a a a a a a a • a a a a • a • a a a a a a a a a a . a rH TH rH Ol Ol OJ CO * rt CO0 0 'D in CO in OJ rH rH 0J rH OJ rH OJ H CO CU OJ *H ^ rH * as CO V0 CT. 'D rH in in 0 OJ N 00 o N OJ rH rv 00 into oo oo crs n in O rH CO rH CO in CO O CO m N ch f in rt •0 rH N in m rH fS. OS (V- CO ^ a a a • • a a a a a a m . • a a a a a a a a a a a a a a a a •H i—(r H OJ OJ OJ CO •H CO rH * CO VjD * N o in o OJ rt in rH N N 0? 00 & 00 VO cu in -0 i—l V0 rH o O rH rH K a ian ® a (T-a. * a a N a ina 00a 00a a 00a * a a a a ina "Ta N a •0a a OSa ina a 00a N a OaS (0a CO• Ual i-l THr H rH cu OJ CO CO rf CO 'O 'O CO in OJ TH rH OJ 1—4 cu Ol tH + OJ OJ OJ aj CO o CD in Tf rH rt VO 00 in 0 cr. oo '•r» cu CO co in vo o:« V0 N 00 vo o CO VO 01 CO rH C". in oo N- vD.® VO vD rH rH '.£)i n N CD o "T CO N O CO N in TH vO in in CO o rf o 0 0 OJ -jO * a a a a ^ a a a a a a a '0a a 00a a a a a a a a COa OaJ a a OJa a oaj a a a a a a a a a . i—t i—rtH OJ »H OJ OJ OJ oo rt ^ vjo CO tf CO CO•0 vjD vO N CU in in co rH rH y-t CO rH oi in OJ OJ 01 10 Ol OJ rt Ul N OS CD OJ in CD <-DrH co ^ rv rH 00 *Hi n cr. CO 0J CO 0 N ^ OJ 01 CO0 D CO CD oo in o o o ** rH N '0 <=> CU COm rH *H ry in N rH CO rH k vo co rH O CO in OJ ^ •0 CO0 1 vu m rH (N- tH N CU V0 (tN^THtr. oin^ojrj^Ncr. vo I p ^ n ^ ^ OJ OJ OJ OJ 01 CO CO CO rt- rf- rf rf m \r in in Ifl v0 vO 'O N N N CO CD 00 01 OS cr. (JiOOoq PQ f H 1-t H H 11 1 2. 90 2. 91 2. 92 2. 94 2. 97 3. 01 3. 05 3. 10 3. 14 3. 19 3. 23 3. 28 11 2 3. 31 3. 35 3. 37 3. 40 3. 41 3. 42 3. 42 3. 41 3. 39 3. 37 3. 34 3. 30 11 3 , 3. 25 3- 20 3. 14 3. 08 3. 02 2. 96 2. 89 2. 83 2. 76 2- 70 2. 65 2. 61 11 4 2. 57 2. 55 2. 53 12 1 0 0 0 0 0 0 0 0 0 0 0 • 36 12 2 1. 09 1. 71 2. 21 2. 62 2. 94 3. 19 3. 37 3. 51 3. 59 3. 65 3. 67 3. 68 12 3 3. 67 3. 66 3. 65 3. 64 3. 64 3. 65 3. 68 3. 73 3. 79 3. 88 3. 99 4- 13 12 4 4. 28 4. 46 4. 63 13 1 0 0 0 0 0 0 0 • 05 • 27 • 49 • 70 • 90 13 2 1. 10 1. 28 1. 46 1. 63 1. 79 1. 94 2. 09 2. 22 2. 35 2. 46 2. 57 2. 67 13 3 2- 75 2. 82 2- 88 2. 93 2. 96 2. 97 2. 97 2. 95 2. 91 2. 85 2. 77 2. 66 13 4 2. 53 2. 38 2. 22 14 1 0 0 0 0 0 0 0 0 0 0 0 • 09 14 2 0 0 • 02 • 54 1. 19 1. 93 2. 69 3. 42 4. 08 4. 65 5. 10 5. 41 14 3 5. 58 5. 60 5. 48 5. 25 4. 91 4. 50 4. 07 3. 66 3. 33 3. 13 3. 14 3. 44 14 4 4. 11 5. 26 6. 41 15 1 0 0 0 0 0 0 0 0 0 0 • 58 1. 36 15 2 2. 12 2. 83 3. 48 4. 07 4. 59 5. 03 5. 40 5. 68 5. 88 6. 00 6. 05 6. 03 15 3 5. 95 5. 81 5. 63 5. 43 5. 21 5. 00 4. 81 4. 67 4. 59 4. 60 4. 72 4. 99 15 4 5. 44 6. 08 6. 73 16 1 0 0 » 73 1. 10 1. 42 1. 69 1. 91 2. 10 2. 26 2. 38 2. 48 2. 55 16 2 2. 59 2. 62 2. 63 2. 62 2. 59 2- 54 2. 47 2. 38 2» 27 2. 13 1. 97 1. 78 16 3 1. 55 1. 29 • 99 9 64 • 24 0 0 0 0 0 0 0 16 4 0 0 0 17 1 0 0 0 0 0 0 0 0 0 0 0 0 17 2 0 0 0 0 • 27 0 0 • 07 • 58 1. 25 2. 01 2- 81 17 3 3. 59 4. 33 4. 98 5. 53 5. 97 6. 28 6- 46 6. 55 6. 54 6. 47 6. 38 6. 32 17 4 6. 33 6. 49 6. 64 13 1 0 0 0 • 80 2- 04 3. 02 3. 80 4. 40 4. 86 5. 21 5. 46 5. 64 13 2 5- 77 5. 86 5. 92 5. 97 6. 00 6. 01 6. 01 6. 00 5- 95 5. 87 5. 73 5. 52 18 3 5. 22 4. 80 4. 24 3. 50 2. 55 1. 36 0 0 0 0 0 0 18 4 0 0 0 19 1 0 0 0 0 0 0 0 0 0 0 0 m2 5 19 2 m0 1 0 0 0 0 . 16 .3 8 .6 4 • 93 1. 24 1. 57 1- 89 19 3 2. 20 2. 50 2. 76 2. 99 3. 18 3. 30 3- 37 3. 36 3. 27 3. 09 2. 82 e. 43 19 4 1. 94 1- 32 • 70 20 1 0 0 0 0 0 0 0 0 0 0 0 1. 86 20 1. 67 m5 0 0 2 0 0 0 0 • 63 1. 12 0 0 0 20 3 0 0 0 0 0 0 0 0 0 0 0 0 20 4 J*. 0 0 .. 21 1 4» 53 5. 17 5. 81 6. 12 6. 15 5. 97 5. 63 5. 17 4. 62 4. 04 3- 44 2. 86 21 2 2. 31 1. 81 1. 38 1. 02 • 73 • 52 • 36 • 27 • 20 • 15 0 0 21 3 0 0 0 0 0 0 0 0 0 0 0 0 21 4 0 0 0 22 1 5. 78 5. 91 6- 05 6. 14 6. 19 6. 22 6. 23 6. 22 6. 21 6. 20 6. 18 6. 17 22 2 6. 16 6. 17 6. 18 6. 20 6. 23 6. 27 6. 32 6. 37 6. 43 6. 48 6. 52 6. 55 22 3 6. 56 6- 55 6. 50 6. 42 6. 28 6. 08 5. 81 5. 46 5. 02 4. 47 3. 30 3. 00 22 4 2. 05 9 94 0 23 1 6. 46 6. 04 5. 62 5. 18 4. 72 4. 27 3. 85 3. 45 3. 10 2. 79 2. 53 2. 33 23 2 2. 18 2. 08 2. 03 2. 01 2. 02 2. 04 2. 07 2. 08 2. 05 1. 98 82 1. 55 23 3 1. 15 .5 9 0 0 0 0 0 0 0 0 0 0 23 4 0 0 0 24 1 3. 11 3. 16 3. 20 3. 28 3. 40 3. 54 3. 70 3. 86 4. 04 4. 21 4. 38 4. 54 24 2 4. 68 4. 81 4. 91 4. 99 5. 04 5. 06 5. 05 5. 01 4. 94 4. 83 4. 69 4. 51 24 3 4. 31 4- 07 3. 81 3. 52 3. 20 2. 87 2. 52 2. 16 1. 79 1. 42 1. 05 • 69 24 4 » 35 0 0 25 1 0 0 0 0 0 0 • 28 • 63 • 89 1. 09 1. 23 1. 32 25 2 1- 39 1. 44 1. 48 1. 52 1. 56 1. 62 1. 69 1. 78 1- 89 2. 03 2. 18 2. 35 25 3 2. 53 2. 72 2. 92 3. 11 3. 28 3. 43 3. 55 3. 62 3. 62 3. 55 3. 38 3. 10 25 4 2. 68 2. 11 1. 55 26 1 0 0 0 0 0 0 0 0 0 0 0 0 26 2 m 11 V 25 40 • 55 • 70 • 84 • 95 1. 03 1. 07 1. 07 1. 00 87 26 3 • 67 9 38 0 0 0 0 0 0 0 0 0 0 26 4 0 0 0 27 1 3. 62 3. 56 3. 51 3. 45 3. 38 3. 30 3. 22 3. 14 3. 05 2. 97 2. 89 2. 82 27 2 2. 74 2. 67 2. 61 2. 55 2. 49 2. 44 2. 40 2. 36 2. 32 2. 28 2. 25 2. 21 27 3 2. 17 2. 13 2. 08 2. 03 1. 97 1. 89 1. 8p 1. 70 1. 57 1- 42 1. 25 1. 04 27 4 • 80 52 .2 5 28 1 0 0 0 0 0 0 i 0 0 • 12 • 72 1. 17 28 2 1. 49 1. 70 i. 84 1. 92 1. 97 2. 00 2. Gti 2. 05 2. 10 2. 17 2. 27 2. 39 28 3 2. 53 2. 70 88 3. 06 3. 24 3. 39 3. 50 3. 54 3. 50 3. 35 3. 05 2. 59 28 4 1. 92 1. 01 9 10 29 1 0 0 0 0 0 0 0 0 0 0 21 94 29 2 1. 50 1. 91 2. 19 2. 37 2. 47 2. 50 2. 47 2- 41 2. 32 2. 22 2^ 10 1. 98 0 29 3 1. 86 1. 74 1. 63 1. 51 1. 38 1. 24 1. 07 • 98 • 64 • 34 0 29 4 0 0 0 30 1 0 0 0 0 0 0 • 38 • 94 1. 38 1. 71 1. 95 2. 12 30 2 2. 23 2. 29 2. 31 2. 31 2. 23 2. 24 2. 20 2. 16 2. 11 2. 08 2. 04 2. 02 30 3 1. 99 1. 97 1. 94 1. 90 1. 85 1. 77 1. 65 l. 50 l. 28 l. 00 9 63 0 C3Q .4 0 0 0 31 1 0 0 0 0 0 0 0 0 0 0 0 0 31 2 0 0 0 0 0 0 0 .26 .6 8 1. 22 1. 79 2. 35 31 3 85 3. 26 3. 55 3. 70 3. 71 3. 56 3. 27 2.85 2. 33 1. 73 1. 11 • 51 31 4 0 0 0 32 1 0 0 0 1. 06 1. 90 2. 44 2. 72 2.81 2. 76 2. 60 2. 33 2. 13 32 2 1. 87 1. 62 1- 41 1. 24 1. 12 1. 06 1. 04 1.05 1. 09 1. 14 1. 16 1. 12 32 3 1. 00 • 75 .3 3 0 0 0 0 0 0 0 0 0 32 4 0 0 0 33 1 3. 06 3. 04 3. 01 3. 01 3. 02 3. 04 3. 08 3.13 3. 19 3. 25 3. 31 3. 37 33 2 3. 44 3. 50 3. 55 3. 60 3. 64 3. 66 3. 68 3.68 3. 66 3. 63 3. 57 3. 50 33 3 3. 40 3. 27 3. 13 2. 95 2. 74 2. 51 2. 24 1.94 1. 61 1. 24 - 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«-» CM CO r- r- r- r* r- 00 00 00 CO 337 APPENDIX 6 CHANGES IN EXPOSURE GRADE WHEN USING DIFFERENT SPECIES FULL SPECIES MINUS POLLUTION PLANTS ANIMALS FUCOIDS " STRONG SET SENSITIVE SPECIES ONLY ONLY ONLY SPECIES' MG1 F78 5.00 4.75 5.50 4.75 4.50 M78 4.75 4.25 5.25 4.25 5.00 4.75 A78 4.75 4.75 5.00 4.75 4.50 N78 4.25 4.50 6.00 4.00 4.75 J79 5.00 4.75 5.50 4.50 5.25 S79 4.50 4.25 5.75 3.75 4.75 MG2 F78 5.25 5.25 5.75 4.25 5.50 M78 5.75 6.00 6.00 4.75 9.00 6.00 A78 6.00 7.00 6.50 4.75 6.00 N78 7.75 6.00 9.00 4.00 6.00 J79 7.25 7.25 6.50 7.50 6.00 S79 7.00 6.00 6.75 4.50 6.00 MG2A S79 7.00 7.75 6.75 4.50 6.00 MG3 F78 8.00 7.75 8.25 3.75 7.75 M78 7.50 7.50 8.25 7.25 8.25 7.50 A78 7.50 7.75 8.25 5.50 7.50 N78 7.75 7.75 8.25 3.75 7.50 J79 7.50 7.50 8.25 7.25 7.50 S79 7.75 7.75 8.25 4.25 7.50 MG3A S79 7.75 7.75 8.75 7.75 7.50 MG4 F78 7.75 7.75 8.00 6.00 7.50 M78 7.50 7.25 7.75 7.25 7.75 7.75 A78 8.00 7.75 8.25 6.50 8.00 N78 8.00 8.00 8.75 8.00 7.75 J79 7.25 7.25 7.25 7.25 8.00 S79 8.00 8.00 8.25 8.00 8.00 MG5 F78 7.75 7.75 8.25 7.75 7.50 M78 7.50 7.50 8.50 7.50 9.00 7.50 A78 8.00 7.75 8.50 7.75 7.75 N78 8.00 7.75 8.75 7.75 7.75 J79 7.50 7.25 8.50 7.50 7.50 S79 8.00 7.75 8.75 7.75 7.75 MG5A S79 8.00 8.00 8.00 8.00 8.25 MG5B S79 5.75 6.00 6.00 4.75 6.0O APPENDIX 5 (Continued) FULL SPECIES MINUS POLLUTION PLANTS ANIMALS FUCOIDS "STRONG SET SENSITIVE SPECIES ONLY ONLY ONLY SPECIES" MG6 F78 A.00 4.25 4.75 3.50 4 .00 M78 4.50 4.75 4.50 4.75 4.50 4 .50 A78 4.25 4.50 4.75 4.00 4.25 N78 4.00 4.25 4.50 3.75 4 .50 J79 4.25 4.25 4.50 4.00 4.50 S79 4.50 4.50 4.75 4.00 4.50 MG6A J79 3.75 3.75 3.75 3.75 3.75 MG7 F78 3.50 3.50 3.75 3.00 3.50 M78 3.50 3.50 . 3.50 ' 3.25 3.50 3.25 A78 3.25 3.50 3.75 2.50 3.25 N78 3.25 3.25 3.50 2.00 3.00 J79 5.50 3.50 3.50 3.50 3.50 S79 3.25 3.25 3.50 3.00 3.25 MG7A J79 2.75 2.75 2.75 2.50 2.50 MG7B J79 2.00 2.25 2.25 1.75 2.00 MG8 F78 2.00 2.00 2.00 2.00 2.00 M78 2.00 2.00 2.00 2.00 2.25 1.75 A78 2.00 2.00 2.00 2.00 2.00 N78 2.00 2.00 1.75 2.50 2.00 J79 2.00 2.00 1.75 2.00 1.75 S79 2.00 2.00 1.75 2.00 1.75 MG8A J79 1.75 1.75 1.75 2.00 1.75 MG9 F78 1.75 1.75 1.50 2.00 1.75 M78lm 1.75 1.75 1.50 2.00 1.75 1.50 M78*m 1.75 2.00 1.75 2.00 1.75 A78 1.50 1.50 1.25 2.00 1.50 N78 1.50 1.75 0.75 2.00 1.50 J79 1.25 1.50 1.25 1.50 1.50 S79 1.25 1.50 1.00 2.00 L.25 MGIO F78 0.50 0.50 0.50 0.25 0.50 M78 0.50 0.50 0.50 1.00 0.50 0.50 A78 0.50 0.50 0.25 1.25 0.50 N78 0.25 0.25 0.25 0 0 J79 0.50 0.50 0.25 1.75 0.25 S79 0.50 0.50 0 1.50 0.50 APPENDIX 5 (Continued) FULL SPECIES MINUS POLLUTION PLANTS ANIMALS FUCOIDS "STRONG SET SENSITIVE SPECIES ONLY ONLY ONLY SPECIES" MG11 F18 0 0 0 0.25 O M78 0 0 0 0 0 o A78 0 0 0 0.50 o N78 0 0 0 0 o J79 0 0 0 1.50 o S79 0 0.25 0 1.25 o SH12 5.75 5.50 5.50 6.00 5.25 5.75 SHI 3 2.00 2.00 2.00 2.25 2.25 2.00 SHI 4 0 0 0 0 0 O SHI 5 0.50 0.50 0.75 0.25 0.75 0. 50 SH16 1.75 1.75 1.25 3.00 1.75 1.75 SH17 6.00 6.00 6.25 5.75 6.00 6.00 SH18 7.75 7.75 8.25 7.75 8.25 7.50 SH19 1.00 1.00 1.00 1.50 1.00 0.75 SH20 2.75 2.75 2.75 2.25 2.50 2.75 SH21 6.00 6.00 6.25 6.00 6.00 6.00 SH22 1.50 1.50 1.50 2.00 1.50 1.50 SH23 5.25 5.50 5.50 5.00 5.25 5.50 SH24 4.50 4.75 5.00 4.00 4.75 4.50 SH25 8.50 8.50 8.25 9.00 7.25 8.25 SH26 5.00 5.00 4.75 6.00 4.25 5.00 SH27 2.75 2.75 3.00 1.50 3.50 2.75 SH28 0 0 0 0.50 0 0.25 SH29 3.00 3.00 3.00 2.75 3.25 3.00 SH30 0 0 0 0 0.25 0.25 SH31 9.00 9.00 9.00 9.00 9.00 9,00 SH32 9.00 9.00 8.75 9.00 8.75 9.00 SH33 8.25 8.25 7.75 9.00 7.50 8.50 SH34 8.25 8.25 8.50 8.25 8.75 8,25 SH35 7.75 7.75 7.50 7.75 8.00 7,75 SH36 5.25 5.00 4.75 6.00 4.50 5,25 SH37 7.00 7.00 7.00 6.00 7.25 7,25 SH38 7.75 7.75 7.75 7.75 8.00 7,50 SH39 7.75 7.00 7.25 7.75 7.25 7,25 SH40 4.75 4.50 5.00 4.50 4.75 4,75 SH41 6.25 6.25 5.75 6.50 5.25 6,25 SH42 2.25 2.25 2.25 2.00 1.75 2.00 340 APPENDIX 5 (Continued) FULL SPECIES MINUS POLLUTION PLANTS ANIMALS FUCOIDS "STRONG SET SENSITIVE SPECIES ONLY ONLY ONLY SPECIES" SH43 1.75 1.75 1.75 1.50 2.00 1 .75 0P44 4.50 4.50 4.50 4.25 4.75 4 .50 0P45 2.50 2.50 2.50 2.50 2.50 2 .25 0P46 0.50 0.50 0.50 1.75 0.25 0.25 OP47 3.75 3.75 3.75 4.00 3.75 3.75 OP48 4.50 4.50 4.25 4.75 4.25 4.25 OP49 1.50 1.50 1.50 1.75 1.50 1.50 0P50 3.00 3.00 3.00 3.00 3.25 3.00 0P51 4.25 4.25 4.75 4.00 4.75 4.50 OP52 3.00 3.25 3.00 3.00 3.00 3.00 OP53 6.75 6.75 7.00 6.25 9.00 7.00 OP54 4.00 3.75 4.00 4.00 3.75 4.00 OP55 9.00 4.00 9.00 4.00 4.50 4.50 OP56 7.75 7.75 8.75 7.75 8.75 7.50 OP57 6.75 8.00 6.75 8.00 6.75 8.25 OP58 4.75 4.50 4.00 5.50 4.00 4.50 OP59 5.75 5.75 5.75 6.00 6.25 6.00 0P60 7.50 7.75 0 5.50 0 7.75 0P61 7.00 7.00 7.00 7.00 9.00 7.25 OP62 5.00 5.00 5.50 4.50 5.25 5.00 0P63 4.50 4.50 4.50 4.50 4.75 4.75 OP64 4.25 4.00 4.25 4.50 4.25 4.00 OP65 2.75 2.75 2.75 3.25 2.50 2.75 OP66 4.50 4.50 4.50 4.50 4.75 4.50 OP67 2.50 2.50 2.50 2.50 2.25 2.25 OP68 3.50 3.50 3.75 3.00 3.75 3.50 OP69 4.25 4.50 4.50 3.75 4.75 4.50 0P70 3.75 3.75 3.75 3.50 4.00 3.75 0P71 3.00 2.75 3.00 3.00 3.00 3.00 OP72 3.25 3.00 2.75 3.50 3.00 3.00 OP73 1.75 1.75 1.75 1.75 2.25 1.75 OP74 3.00 2.75 2.50 4.00 2.50 2.75 OP75 5.75 5.75 5.75 5.50 6.00 5.75 OP76 3.75 3.50 3.50 3.75 3.75 3.75 OP77 2.50 2.75 2.50 3.25 2.25 2.50 OP78 2.50 2.50 2.50 3.25 2.75 2.75 341 APPENDIX 5 (Continued) FULL SPECIES MINUS POLLUTION PLANTS ANIMALS FUCOIDS "STRONG SET SENSITIVE SPECIES ONLY ONLY ONLY SPECIES' OP79 3.00 3.00 2.75 3.00 2.75 2.75 0P80 4.25 4.00 4.50 4.00 4.25 4.50 OP81 7.75 5.25 8.75 5.00 5.00 5.25 0P82 7.50 2.50 2.50 2.50 2.50 2.50 0P83 4.75 4.75 4.75 4.50 4.25 4.50 342 APPENDIX 6 REPORT TO SOTEAG ON OIL POLLUTION AT MAVIS GRIND, SHETLAND. • 1. Introduction I am a research student working on the effect of wave exposure on rocky shore ecology in Shetland. I have concentrated my efforts on a number of sites around Mavis Grind, and one of them (MG2) is approximately 20 m. east of a stream which carries oil from the asphalt plant at Mavis Grind The oil from the asphalt plant seems to be a continuous seepage which has caused the blackening of vegetation around the stream. Where it enters Sullom Voe there is a reduction in littoral species and always an oil sheen visible on the surface of the water. I hope the work I have done at MG2 will indicate the effect of the oil on the nearby shoreline. I have recorded the abundance of species on this site, using the same method as the Oil Pollution Research Unit (OPRU), on the following occasions: 10 February 1978 30 May 1978 21 August 1978 15 November 1978 14 June 1979 7 October 1979 2 March 1980 In addition, a new site (MG2A) situated approximately 30 m. south of the stream was recorded on 7 October 1979 and 2 March 1980. 343 2, Summary of Species Changes at MG2 Superficially, UG2 has the flora and fauna of a moderately sheltered site. However, closer inspection reveals a number of changes that have taken place throughout 1978 and 1979. a) A slime of blue-green / green algae appeared in the topshore region in autumn 1978 and have since remained persistently abundant despite dessication in the summer months. The dominant species (identified by J.R. Kitchenside, Imperial College) appear to be Ulothrix pseudoflacca (green alga) together with Phonnidium sp. and Lyngbya sp. (blue-green algae). b) Enteromorpha sp. has been present since recording began (Feb, 78), and shows strong seasonality. Common in Feb 78, it increased in abundance to Liay 78 and then decreased to absent by Nov 78. There was another large increase in spring 79, but the peak was not as great as spring 78. March 80 records reveal that the situation is being repeated this year. c) Pelvetia canaliculata. In Feb 78 there were plenty of individuals of this specieB at UG2, although they were mainly old and withered specimins. They gradually decreased in abundance until many sporelings were noted in Oct '•'9. Many of these survived into March 1980, thereby increasing the abundance and vortical range of this species„ d) Fucus spiralis / Fucus vesiculosis. Below the Pelvetia zone, these two fucoids have been moderately abundant, but again mainly as older and more ragged specimins. Lower shore F. vesiculosis appeared to be more healthy. However, in June 79, a large number of fucoid sporelings were noted in the topshore. At first it was impossible to differentiate these to species level, but by March 80 they had grown sufficiently to make this possible. e) Balanus balanoides (Acorn Barnacle) and Littorina saxatalis, L. littorea, L. littoralis (winkles). A gradual decline in abundance was recorded between February abd November 1978. Since then these species have remained at constantly low population levels. f) Patella vulftata (Common Limpet). The abundance of limpets on the top and middle shore has decreased, leaving a stable lower shore population. 344 The Extent of Pollution Effects. Immediately next to where the stream enters the voe (at point X), the shoreline is extremely oily. A fev; oily fucoids are present with a blue-green / green algal slime coating the rocks. The only animals present are a few barnacles. The situation improves within a few metres of this point and up to LrG2. East of Ml— and up to point Y, the abundance of fucoids and littorinids decreases, due almost certainly to the increased exposure of this part of the shoreline and not due to the oil pollution. Point Y is similar in exposure to MG1 which is unaffected by oil and has similar quantities of fucoids, barnacles, littorinids, and limpets. South of the stream is a beach consisting of angular blocks of rock which are lacking fucoids and attached animals as might be expected on such a shore. Further south is a rock outcrop on which site MG2A is situated. On both occasions that records have been taken from this site, the ecological situation appears similar to M§2. Beyond MG2A is a small beach and a new shoreline formed by rock dumping from a quarry. This shoreline is at an early stage of colonisation and supports mainly Enteromorpha intestinalis and Porphyra umbilicalis. 345 West of Mavis Grind, there is a stream from the asphalt plant into Culsetter Voe. On this side of Mavis Grind, an oil sheen has only been noticed on one or two occasions, but the stream does carry a large amount of sediment into the voe from works associated with the asphalt plant. In this area the voe is only about 1 m. deep at low tide, and already a sediment pan is building up where the stream enters the voe. No obvious biological effects have been noticed at site MG3, situated approximately 20 m. west of this point. However, in March 1980 a clear band of topshore Enteromorpha was noticed around the end of the voe to the east of MG3 and around where the stream enters. This is unlikely to be due to a reduction in salinity since no such reduction has been noted 4n two previous sampling occasions. It is more likely to be due to a possible deterioration in the water quality of the stream from the asphalt plant. 4. Conclusions a) There appears to be a continuous trickle of oil from the asphalt plant into Sullom Voe at Mavis Grind. b) Spccics changes due almost certainly to oil pollution have occurred over a distance of up to 30 m. east and south of where the stream enters the voe. c) Deterioration of the shoreline flora and fauna occurred during 1978 and starting possibly before then. The unhealthy situation is typified by large flushes of Enteromorpha in the spring and the presence of an extensive algal slime on the topshore. d) The settlement and growth of topshore fucoids in 1979 indicates the beginning of a recovery in the shoreline flora and fauna. The barnacles, littorinids, and limpets have not yet begun their recovery which in oil pollution incidents is usually expected after the fucoids. This may be a natural delay, or it may be due to the continuing trickle of oil pollution into the voe. 346 a) There is an increased sediment discharge from the stream into Culsetter Voe to the west of Mavis Grind* This is causing the building of a sediment pan in a shallow part of the voe. It is likely that a possible deterioration in the water quality of this stream is responsible for a high level flush of Enteromorpha in the vicinity. R.A.D. Wright 11 March 1980 APPENDIX 347 c r 2t e V VP SOIL PRESSURE CEII Type 0234 DESCRIPTION This pressure transducer has been specifically designed to meet the demands of soil stress measurement. Being fluid filled the diaphragms exhibit virtually zero deflection under load and the active/total area ratio has been designed so that the intrusion of the cell into the material under study has the minimum effect on its properties. The transducer utilises a solid state silicon pressure transducer as the basic sensing element coupling extreme robustness with high output. KULITE SEMICONDUCTOR PRODUCTS, INC. • 1039 Hoyt Avenue • Ridgefield, New Jersey 07657 • Tel: 201-945-3000 • Cable: Kultung • Telex: 135 458 EUROPEAN SUBSIDIARIES: KULITE SENSORS LTD. • 11/12 Brighton Hill Parade • Sullivan Road • Basingstoke, Hants, England • Tel: 0256-61646/7 • Telex: 8584 KULITE INTERNATIONAL S.A.R.L. • Siege Social et bureaux, 41 rue Parmentier 92600 • Asnieres, France • Tel: (1) 733-13-62 • Telex: 620 256F KULITE SEMICONDUCTOR GmbH • Postfach 1527 • 6238 Hofheim/Ts* West German • e- SPECIFICATIONS INPUT PRESSURE RANGES: 0-2 Bar, 0-3.5 Bar, 0-7 Bar. PRESSURE LIMITS: Twice rated pressure range. ELECTRICAL EXCITATION: 7.5 V DC, 10 V DC max. OUTPUT FULL RANGE OUTPUT: 100 mV (nom) ZERO OUTPUT: ±5 mV max STATIC ERROR BAND: ±1% FRO max ENVIRONMENTAL COMPENSATED TEMPERATURE RANGE: 0 to +30 C OPERATIONAL TEMPERATURE RANGE: —15°C to +40°C THERMAL ZERO SHIFT: ±0.03% FRO/°C THERMAL SENSITIVITY SHIFT: ±0.03% FRO/°C PHYSICAL ACTIVE/TOTAL AREA RATIO: 43% DEFLECTION: 0.0025 mm (.0001") at rated pressure ELECTRICAL CONNECTION: Sealed cable assembly in lengths up to 10 metres (33 feet) OUTLINE 036,0 (1.42) ACTIVE DIA 4 CONDUCTOR,PVC INSULATED SHIELDED CABLE 03,2 (.125) (LENGTH TO BESPECIFIED 055,00 (2.165) PART NO. TYPE DIM T 0234-1 WITH REINFORCING PLATE 12,7 (.500) 0234-2 WITHOUT REINFORCING PLATE 10,0 (.394) 0234-30 WITHOUT REINFORCING PLATE 12,04 (.474) 0234-40 WITH REINFORCING PLATE 14,73 (.580) Continuous development and refinement of our roducts ma result in s ecification chan es without notice. rrrrx ..JH'n.-. J '..LJfl*L' JW^-H.. i>. ..vi-ervrr.-sr.?r- THE BHL 5000 M1NIGRAPH •SBBSBSKCMBE • 8 channels. • Portable - weight 10kg. • Uses Bell and Howell 7-300 • a.c. or d.c. operation. series galvanometers. • Power consumption 60VA. • 8 speeds, 1 to 1000mm/sec. • Instant recording due to use of • Writing speed 400m/sec. Tungsten Halogen lamp. The Bell and Howell BHL 5000 Minigraph is a low cost Due to the tungsten light source, the recorder is portable light beam direct writing recorder capable of operational within milliseconds from "switch-on". The writing eight channels of information on 150mm (6 inch) ability to switch from a.c. to d.c. makes it particularly wide direct print paper. To reduce cost of paper, when suitable for mobile applications. recording only two or three channels, smaller widths of paper can be used. The standard version is fitted with a time marker generator. Full width flash timing is available as an The recording light source is a 20 watt tungsten halogen optional extra. lamp which, with 7-383 galvanometers, give a writing speed in excess of 400 metres per second to record rise times of less than 300 microseconds. BellbHoluell 2349 Specifications Mlnlgraph BHL 5000 Active Data Channels Up to 8. Signal Inputs Individual Input to each galvanometer using electrically Isolated 3 pin sockets. Galvanometer Bell and Howell 7-300 series. Frequency Response Up to 2kHz using the 7-380 and 7-383 galvanometers specially designed for use with tungsten light recorders. Optical Arm 220mm. Light Source 20 watt Tungsten Halogen lamp. Writing Speed 400m/s using 7-383 galvanometer and Oscllloscript 'D' paper. Recording Paper 150mm wide direct-print paper wound on 25.4mm (1 inch) core with emulsion side in. Will accept smaller widths. Paper Drive d.c. servo system. Paper Speed 8 speeds 1, 5,10, 25, 50, 100, 250 and 1000mm/sec. Grid Lines Optical — automatically exposed at 2mm Intervals with every fifth line accentuated. Time Marker Crystal controlled timer generating pulses at 0.01, 0.1,1 and 10 seconds. Automatically interlocked with speed control. Remote Operation Via 5 pin socket — start stop and speed control either by external resistor or voltage. Controls and Indicators Mains on/off with indicator lamp. 5 pushbutton speed control. 1, 5, 25 and 100mrn/s and X10. Grid and trace intensity controls. Paper contents indicator. a.c. or d.c. selector switch (mounted on rear panel). Mains selector switch (mounted on rear panel). Power Supplies 200-250V, or 100-125V at 48-65HZ and 11 to 15V d.c. 22 to 30V d.c. via optional ballast resistor. Power Consumption 60VA on mains. 4A on normal 12V battery. Dimensions Width 260mm (10V4 inch). Height 162mm (6 >A inch). Depth 347mm (12'/« Inch). Weight 10kg (22 lbs). Optional Accessories Proto-muff — Part No 234872-0005. Full Width Flash Timing. Fitted at time of order. Due to continuing development Bell and Howell reserve the right to amend the above specifications without prior notice. Manufactured in England by ELECTROniCSGinSTRUmEnTS Division LENNOX ROAD BASINGSTOKE HAMPSHIRE RG22 4AW ENGLAND TEL: BASINGSTOKE (0256)20244 TELEX: 858103 TELEGRAMS. CONSOLENG BASINGSTOKE Belle Howell LimiTED United States of America, Bell & Howell Co.. Electronics & Instruments Group. 360 North Sierra Madre Villa, Pasadena, California 91109. Australia, Bell & Howell Australia (Pty) Ltd., Netherlands, Bell & Howell GmbH., P.O. Box 4778, 55-69 Murray Street, Sydney, Vlaardingweg 23, 3044 CJ Rotterdam, New South Wales 2001. Postbox 10054, 3004 AB Rotterdam. England, Bell & Howell Ltd., South Africa, Bell & Howell South Africa (Pty) Ltd Lennox Road, Basingstoke, Hampshire RG22 4AW. Micro House, 101 Juta Street, P.O. Box 31239, France, Bell & Howell France. S.A., Braamlontein, Johannesburg 2001. Electronics & Instruments Division, 112 Rue Des Solets West Germany, Beli & Howell GmbH, Silic 138, 94523 Rungis. Cedex Electronics & Instruments Division, 6360 Freidberg, Postfach 1230 Italy, Bell & Howell Italia SpA , Via Inverigo 6, 20151 Milan tales end service facilities in other countries. A comprehensive network of specialised representitivei providei full Printed in the U K OC|4|78|5m Bulletin BHL 5000 April 1978 2350 Galvanometer Type 7-383 Large mirror High Sensitivity Greoter Deflection Capability The Bell & Howell 7-383 galvan- ometer has been designed to improve the performance of tungsten light source oscillographs. Its higher sensitivity combined with the large mirror also makes the 7-383 extremely versatile in appli- cations where only a low driving current is available, or when the operator wishes to deflect the trace over a wide excursion. The Bell & Howell 7-383 galvan- ometer can be interchanged with any standard 7-300 Series galvan- ometer, the only difference being that the 7-383 has no turret lens. BellbHoujell CEC Division 7383/1077 SPECIFICfiTIOflS Type 7-383 Galvanometer 7-383-0001 7-383-0002 Optical Arm: 9.0" 11.5" Useful Frequency Range: 0-500 Hz 0-500 Hz Per Unit Damping 0.64 0.64 Resonant Frequency 1600Hz 1600 Hz Sensitivity (inch/ma) 0.036 .046 Sensitivity (inch/volt) 1.785 2.270 Undamped dc Sensitivity (ma/inch) 5.9 4.7 Damping Resistor (driving source impedance) 20 Ohms 20 Ohms Terminal Resistance 75 Ohms 75 Ohms Galvanometer Unbalance 15 Mils 15 Mils Maximum non-linearity (% of ±2" deflection) ±1% ±1% Maximum Safe Current 75 ma 75 ma Zero Return 25 mils 25 mils Pole Spacing 40 mils 40 mils Physical Features The 7-383 is interchangeable with all standard Bell & Howell 7-300 Series galvanometers. Q] Belle,Houjell CEC Division 360 SIERRA MADRE VILLA* PASADENA, CA 91109 Miniature Signal Conditioning Modules BHL-5107 Resistance Bridge Conditioning/ Amplifier The Bell and Howell BHL-5107 is a compact extremely versatile module designed for use with d.c. bridge transducers and complete or fractional strain gauge bridges and platinum resistance thermometers. It provides a variable bridge supply, adjusted by a preset front panel control, from 2.5 to 12 volts at 100mA. a BEUCHouieu t Facilities are available for remote sensing of the ihift mv f.». xero bridge supply which can then be measured at the front pnnni test points. For simplicity of operation the high performance high gain amplifier is calibrated in span from 1 millivolt to 1 volt. This enables the operator to "dial up" the appropriate transducer sensitivity to give amplifier full range output. Three basic ranges 10 millivolt, 100 i-bol-S 1 millivolt and 1 volt can be selected by a front panel •<» I cal I switch and a 10 turn calibrated vernier control iA provides fine control within each range. The amplifier features very low noise, high stability and linearity, V col y z col 2 high common mode rejection and wide dynamic range. In order to achieve critical balance of the bridge configuration, the gain of the amplifier is greatly Upply increased (>106) by operation of the biased balance scale * TRANSDUCER _ , -f^ switch. The balance condition is indicated on LED's. AMPLIFIER ^r BHL 5107 Various outputs are available: low power output for tape and low frequency galvanometers, ± 10V buffered output for digital voltmeters or data loggers, ACTUAL SIZE and for driving high frequency fluid damped galvanometers the variable sensitivity power amplifier can be preset to current limit within the range 10-80mA. The current output can also be used for Bridge supply 2.5 to 12V at up to control systems 0-10mA, 0 to 20mA or 4 to 20mA. 100mA. Provision for 1A, Vi full bridge The shift control, independent of scale control, and PRT. provides zero or offset of the output signal. The amplifier section of the BHL-5107 can be used Remote sensing bridge supply. independent of bridge configuration by isolation switch Calibrated balance control. on the p.c.b. LED balance indicators. Dynamic and shunt calibration. Two types of calibration control are provided. The first Calibrated signal sensitivity enables the output scale to be set in engineering units. range 1mV to 1 volt for f.s.d. The second is to apply a shunt calibration resistor ligh across one arm of the bridge. High gain (10,000), high accuracy amplifierm . Although designed for multi-channel operation the High stability x0.1% over 12 BHL-5107 is complete with its own stabilised power months. supply energised from a compact mains transformer. 4 outputs ± 10V, tape, Isolation of signal earth gives flexibility of signal connection. For operation on 12 or 24 volt d.c. supply magnetically and fluid damped the mains transformer can be replaced with d.c. to galvanometers. d.c. converters. Application of the BHL-5107 may be Self contained mains power extended considerably by use of compatible Bell and supply. Howell Miniature Modules to provide a complete signal Range of mounting cases. conditioning system. Can be used as amplifier only. BellbHdluell L 354 Specifications BHL-5107 Bridge Conditioner/Amplifier BRIDGE CONDITIONER Voltage Constant voltage — adjustable 2.5 to 12V with local or remote sensing. Panel mounted test points. Current Up to 100mA. Resistance Up to 2kf2 — higher with derated amplifier specification. Completion Up to 3 dummy arms may be fitted on turret lugs. Balance 10 turn vernier dial with helical potentiometer. Range sensitivity by internal resistor mounted on turret lugs. Zero Multi-turn cermet potentiometer, screwdriver operation. Range by internal resistor mounted on turret lugs. LEO Indicator* Zero and balance indication by two LED's. Calibration Panel mounted switch provides 2 position internal shunt calibration. Alternatively an external resistor may be called up. AMPLIFIER (Note Bridge can be Isolated to allow use of amplifier only.) Input Ranges Switched 10mV, 100V and IV for full output, with 10 turn calibrated vernier providing continuously variable sensitivity down to 1mV for full output. Resistance 10Mfl balanced differential. Ollset current <50nA. Filter Optional low pass 6dB/octave. Protection Against continuous overload of ± 15V d.c. or 200V for 1 ms. Accuracy <±0.5% at full vernier range and ± 1 % at 10% of range. Linearity <±0.1% FRO. Stability Time <±0.1% FRO over 1000 hrs. Temperature <±0.05% FRO/'C. Repeatability <±0.1% FRO. Bandwidth Preamplifier d.c. to 50kHz (- 3dB). Power amplifier d.c. to 25kHz (-3dB). Common Mode Operation ±6V. Rejection >100dB d.c. to 1kHz. Limit ± 15V and 200V tor 1 ms. Nolae <5mV pk to pk r.t.i. Calibration Panel switch injects d.c. or square wave, 50% ot full output, other values to customer requirements. Output Preamplifier 1 ±10V. Impedance <111. Provision for buffer resistor. Preamplifier 2 Low frequency galvo output with built-in damping and choice of matching resistors by p.c.b. mounted switch. Preamplifier 3 Tape — range selected by internal resistors. Power amp ±80mA into <100J1 with variable limiting control on p.c. card in two ranges 10 to 20mA. 20 to 100mA. Panel mounted screwdriver control varies sensitivity. 10kU output impedance. Shift Full scale by screwdriver operated panel mounted control for galvanometer outputs. Protection Protected against short circuit of unlimited duration. GENERAL Isolation All inputs and outputs isolated from earth. Power requirement 100 to 120V or 200 to 250V 48-425Hz (selected by fuse link) 6VA or 12V d.c. to d.c. inverters at extra cost. Temperature range Operating 0 to 50°C operating. Storage — 20"Cto +85"C. Dimensions Width 50.8mm (2 inch). Height 70mm (2V< inch). Depth 184mm (7V4 inch). Weight 500g. Housing Any of MSCS range. Due to continuous development we reserve the right to amend specifications without notification Manufactured in England by ELECTROniCS&inSTRUmEriTS Division LENNOX ROAD BASINGSTOKE HAMPSHIRE RG22 4AW ENGLAND TEL: BASINGSTOKE (0256)20244 TELEX. 858103 TELEGRAMS: CONSOLENG BASINGSTOKE Bell&Hdujell LimiTED nited States of America, Bell & Howell Co.. Electronics & Instruments Group, 360 North Sierra Madre Villa, asadena, California 91109. ustralla, Bell & Howell Australia (Pty) Ltd., Netherlands, Bell & Howell GmbH., .0. Box 4778. 55-69 Murray Street, Sydney, Vlaaedingweg 23, 3044 CJ Rotterdam, ew South Wales 2001. Postbox 10054, 3004 AB Rotterdam. land, Bell & Howell Ltd.. South Africa, Bell & Howell South Africa (Pty) Ltd. ennox Road, Basingstoke. Hampshire RG22 4AW. Micro House, 101 Juta Street, P.O. Box 31239, ranee, Bell & Howell France, S.A.. Braamtontein, Johannesburg 2001. lectronics & Instruments Division, 112 Rue Des Solets. West Germany, Bell & Howell GmbH. lie 138. 94523 Rungis, Cedex. Electronics & Instruments Division, 6360 Freidberg Postfach 1230. aly, Bell & Howell Italia SpA., Via Inverigo 6, 20151 Milan, comprehensive network of specialised representatives provides full sales and service facilities in other countries. tinted in the United Kingdom 5107/A/OC/0280 PRESSURE SENSOR Type Number •023 •••••4 • Pressure Range 2 .Bar Serial Number 2858 CALIBRATION RECORD Se itivity 88.74 mV Test Temperature 22 °C Excitation •10.0 •••••0 • Volts DC Non-Linearity <±0.2 % FRO Hysterisis & Non Repeatability r.°.*.?f... % FRO Input Resistance •53 •3 • • ohms Output Resistance 381 ohms 2 0 5 Compensated Temperature Range 7. . . °C to t?. . °C Thermal Zero Shift ^P/.^.... % FRO./°C Thermal Sensitivity Shift QUALITY CONTROL Signature 30.3.79 Dc ELECTRICAL CONNECTIONS Input + RED SHAPE INSTRUMENTS LTD. Transducer House, Station Approach, Input BLUE Wokingham, Berkshire RG11 2AP Telephone Wokingham (0734) 791111 Output + YELLOW Output - WHITE 356 lillilllirtificat *lliil i lib lillliiiiiii PRESSURE SENSOR Type Number 9??A Pressure Range ?. ... Serial Number CALIBRATION RECORD S' }itivity 72..S.3 mv Test Temperature ?? °C Excitation IP.-P.Q.... Volts DC Non-Linearity ^tP.-.V? % FRO Hy.sterisis & Non RepeatabilityrrP.-.0.??... % FRO Input Resistance 513 0hms Output Resistance 361 0hms Compensated Temperature Range 7.2P. °C to t?.5. °C Thermal Zero Shift <:rP.-.Ql.... % FR0./°C Thermal Sensitivity Shift ' JL QUALITY CONTROL Signature n * 30.3.79 ./ ELECTRICAL CONNECTIONS Input + RED SHAPE INSTRUMENTS LTD. Transducer House, Station Approach, InDUt - BLUE Wokingham. Berkshire RG11 2AP F ; Telephone Wokingham (0734) 791111 Output + YELLOW Output - WHITE IS ! ii mil ficat 11 ill| | PRESSURE SENSOR Type Number 0234 Pressure Range 2 Bar Serial Number 2856 CALIBRATION RECORD Sr ^itivity •81.4 ••••••••7 • mV 22 Test Temperature °C Excitation •10.0 ••••••••0 • Volts DC Non-Linearity <±0.2 % FRO Hysterisis & Non Repeatabi 1 ity^r.0.*.??.... % FRO Input Resistance 493 ohms Output Resistance 340 ohms -20 +35 Or Compensated Temperature Range °C to • • • • u Thermal Zero Shift <-0.91 % FRO./°C Thermal Sensitivity Shift <.-0.03 . r /o\ m. \°c 1 1 QUALITY CONTROL L/a Signature it" 30.3 79 Di } 0 ELECTRICAL CONNECTIONS KttJJ Input + ! SHAPE INSTRUMENTS LTD. DLUlOT TTPi Transducer House, Station Approach, Input ' Wokingham, Berkshire RG11 2AP : Telephone Wokingham (0734) 791111 Output + YELLOW Output - WHITE 358 Csfftifieat© of Caiifemfei©3su PRESSURE SENSOR Typo Number on 3 4- CL Pressure Range • ••••• * • • Serial Number i?>37 CALIBRATION RECORD Se^/fcivifcy a3- >°> -H.V Test Temperature i °c Excitation . Volts DC , Non-1, i neari tv ^FRO i j Hysteresis & Non Repeatability f-.^.'/fi °/oFRO ' Input Resistance Output Resistance . . T~.. ohms Compensated Temperature Range £?. °C to'MO oc Thermal Zero Shift - Thermal Sensitivity Shift P::%FRO./°C QUALITY CONTROL Si jature Date 2 - /p. • "7 1 ELECTRICAL CONNECTIONS Inpu t P SHAPE rabrumertB fcd Input TRANSDUCER HOUSE. STATION APPROACH. : Output WOKINGHAM, BERKSHIRE RG11 2AP j Telephone Wokingham (0734) 791111 i.. Output VELLOW 359 iil ificat m 6ti PRESSURE SENSOR Type Number Q23.4. Pressure Range 2. EAR Serial Number 313A CALIBRATION RECORD Sensitivity .... mV A Test Temperature .7 °C Excitation V? Volts DC Non-Linearity % FRO (i o i Hysterisis & Non Repeatability . % FRO Input Resistance 47J- ohms Output Resistance 313 ohms Compensated Temperature Range -20 °C to -t39. °C Thermal Zero Shift Q...QQ3.. % FR0./°C Thermal Sensitivity Shift P...Q3... % FR0./°C QUALITY CONTROL Signature Date 7.-2.8i-Bi ELECTRICAL CONNECTIONS Input + RED Input - BLUE Output + ' YELLOW Output - WHITE Kulite Sensors Limited 11-12, Brighton Hill Parade, Sullivan Road, Basingstoke, Hampshire, RG22 4EH, England. Telephone: Basingstoke 61646-7.