Zostera marina monitoring

2004 Expedition Report

Prepared by Kevan Cook

Supported by

Full Reference: Cook, K., 2004a. Report on 2004 Isles of Scilly Zostera marina survey. Acknowledgements

The author would like to thank the following for their help and support:

Colin Sturmer Duchy of 's Office

Geoff Penhaligon, Harbourmaster St Mary's, Isles of Scilly

Cyril Nicholas English Nature

Jim Heslin St Mary's Underwater Centre

Island Carriers

And to all the volunteers that gave so readily of their time and effort and without whom, none of the survey work would have been possible.

2 Contents

Acknowledgements ...... 2 Contents...... 3 Abstract ...... 4 1 INTRODUCTION...... 5 1.1 The Expedition ...... 5 1.11 Expedition Management...... 6 1.12 Expedition Members...... 6 1.13 Expedition Finance...... 7 2 Zostera marina Monitoring ...... 7 2.01 Aims of the survey...... 8 2.02 Locations ...... 9 2.03 Method...... 9 2.04 Data Analysis...... 10 2.1 Data Analysis for 2004...... 12 2.2 Analysis of Time Series Data ...... 14 2.21 Leaf Infection ...... 14 2.22 Plant Size Distribution and Plant Density...... 16 2.23 Mean Plant Density ...... 19 2.24 Mean Biomass Index ...... 20 2.3 Individual Bed Reports...... 21 2.31 Old Grimsby Harbour, Tresco ...... 21 2.32 Higher Town Bay, St. Martin’s ...... 23 2.33 Broad Ledge, Tresco...... 25 2.34 West Broad Ledge, St Martin’s ...... 26 2.35 Little Arthur, ...... 27 2.4 Discussion and Future Work ...... 29 3.0 REFERENCES...... 30

List of Figures Figure 1 IOS 2004 Team Members ...... 6 Figure 2 A Quadrat...... 9 Figure 3 Diver sampling Zostera (Picture courtesy of Ben Crossett, 2003)...... 11 Figure 4 Mean percentage number of leaves infected at survey sites...... 15 Figure 5 Maximum leaf lengths at survey sites ...... 17 Figure 6 Distribution of maximum leaf lengths at survey sites...... 18 Figure 7 Mean Plant Density per 0.0625m2 at survey sites ...... 19 Figure 8 Mean Biomass index at main survey sites...... 21 Figure 9 Location of sample points and individual plant densities, Old Grimsby Harbour...... 23 Figure 10 Location of sample points and individual plant density, Higher Town Bay ...... 24 Figure 11 Location of sample points and individual plant density, Broad Ledge ...... 26 Figure 12 Location of sample points and individual plant density, West Broad Ledge ...... 27 Figure 13 Location of sample points and individual plant density, Little Arthur...... 28

3 Abstract

A total of 9 people took part in the 2004 expedition to survey the Isles of Scilly Zostera marina beds during the week period 31 July – 7 August 2004. During this time the volunteer divers carried out full Zostera marina monitoring dives on the five main Zostera beds with the beds at Rushy Bay and Bar Point being only partly surveyed. After the success of the transect method of surveys in 2003, these are again included.

Zostera plant densities follow a similar pattern from that seen in previous years with the bed at Little Arthur continuing to have the greatest mean plant density. The bed with the biggest change is that at Old Grimsby Harbour which, although remaining highly patchy in nature appears to have removed from the low plant density recorded in 2000. Evidence of damage to the rhizome systems from the swinging mooring chains is still present. This patchy nature of Zostera growth was observed at a number of sites although the reasons for this are not as obvious as at Old Grimsby Harbour. The plant density in the bed at West Broad Ledge, St. Martin’s is now low enough after a slow decline in plant density from August 1997 to raise concern for its long term survival. The bed at Little Arthur continues to thrive with record plant density recorded in 2004.

Infection by the parasitic slime mould Labrynthula remains at similar levels to those recorded in 2003 though there was another noticeable reduction in the amount of infection in the bed at Old Grimsby Harbour, Tresco which had the lowest mean percentage leaf infection of all the beds surveyed and is at record low levels for this bed.

Further surveys to monitor environmental factors and more frequent sampling of the beds are suggested to better assess the impact on the health of the Zostera beds of anthropogenic impacts and variability in seasonal growth patterns.

4 1 INTRODUCTION

The Isles of Scilly, lying some 40km south west of Lands End, are the most westerly land mass of Great Britain and are comprised of approximately 200 granite islands and rocks separated by a shallow sea. The seafloor between the islands is mainly comprised of a mixture of sands and smaller pebbles with a distinct decreasing size gradient in material from west to east. The five main islands; St. Mary’s, St. Martin’s, Tresco, and St. Agnes are inhabited and support farming, fishing and are a popular tourist destination.

The islands are a variety of unique compositions of natural history as a result of the combination of their physical environment and climate. Rare indigenous plants, as well as exotics more characteristic of subtropical climates, thrive on the Islands. The low level of traffic on the roads and plentiful windbreaks made from hedges and pines provide ideal conditions for a variety of birds.

The marine environment is also shaped by the extreme physical conditions. The rocky shores of the western islands are so extreme that the scientific classification of shore- types had to be extended to include a special category for Scilly - the 'super-exposed'. Below the low-water mark, only those species that are able to withstand periodic inundations of the full force of the Atlantic are able to survive. On the more protected eastern seaboard by contrast, sheltered, deep-water habitats are home to colonies of various delicate species such as sea fans and branching sponges which often have southerly distributions.

At the opposite end of the scale of exposure to the battered western shores, the sea bed inside the archipelago is very sheltered. Sediments derived from the granite bedrock are carried by tides and waves into the sheltered inter-island basin and deposited there. These shallow and sheltered inter island waters provide an ideal marine environment for the growth of Zostera marina, which grows in large beds on the sandy sediments found there.

Although deprived of the nutrient sources that are common to the inshore waters of mainland Britain, the waters around Scilly support a wealth of marine life, including numerous commercial species and an important colony of the Grey Seal (Halichoerus grypus).

1.1 The Expedition The 2004 expedition took place between 31st July and 6th August 2004 and was the thirteenth consecutive year in which volunteers visited the Isles of Scilly to carry out surveys of the coastal waters around the islands. The majority of the team were volunteers with previous experience of surveys in the Scillies though some new volunteers were also able to take part.

The main objective of the 2004 expedition was to repeat surveys of the main Zostera marina beds surveyed in previous years also noting the occurrence of any Sargassum muticum within the beds.

5

1.11 Expedition Management The expedition was planned and led by Kevan Cook and assisted by Tom Reid and Ben Thompson.

Other members of the expedition team carried out various other tasks of the associated with the work of the expedition.

1.12 Expedition Members The following people took part in the 2004 Isles of Scilly Expedition:

Figure 1 (From Left to Right) Claire Hinton, Kevan Cook, Karen Knapp, Tom Reid, Jo Simpson and Ben Thompson. (Picture courtesy of Tom Reid)

Also taking part: Dean Foden Jo Foden Natalie Jones

The team used the RIB EVA as their dive platform. In this we were also greatly assisted by Cyril Nicholas from English Nature also acted as Cox’n and guide round the islands.

6 1.13 Expedition Finance The expedition was funded in part by volunteer contributions and by a grant from English Nature to whom the author would like to acknowledge the part they have played in maintaining the surveys. Assistance was also received from the Duchy of Cornwall, in the form of use of their boat shed as a dive store and mooring for the RIB.

2 Zostera marina Monitoring

Seagrass beds were identified under Agenda 21 as being of vital importance and worthy of preservation. They are ecosystems of high productivity and are found in sheltered shallow marine conditions. They are also environmentally susceptible to natural and human related activities, such as climatic changes, sea level rise, dredging and fill activities, sedimentation, sewage discharge and shoreline development. Zostera marina is an important species both ecologically and economically because it provides critical habitat for a range of invertebrates and fish, it protects coastlines from erosion, it causes increased sedimentation leading to enhanced recycling of nutrients and improves water clarity (IGC, 1996).

Zostera marina is a marine angiosperm and together with Z. angustifolia and Z. noltii are the only marine flowering plants found in UK waters. The flowering plants appear markedly different from the non-flowering ones in that they have extended stems containing the flowers growing from the rhizomes with small leaves off the main stem. The leaves of the plants die back at the end of each summer / autumn and then regrow in the spring with the rhizomes, the root system, remain in place. However, although Zostera can reproduce both sexually and vegetatively Grassle and Grassle (1978) suggest that due to the vigorous rhizome growth of this and other seagrasses, and their wide distributions and ecological success, vegetative reproduction generally prevails. Flowering stems have been noted on several Zostera plants within the beds surveyed, however it is not known whether any of the resulting seeds are viable.

The distribution of Zostera along the south coast extends from the beds in the Scilly Isles eastwards along the channel as far as Studland Bay in Dorset in full marine but sheltered conditions in sand or mud substrates. However, it can also found in some brackish lagoons such as the Fleet in Dorset.

Annual surveys of the Zostera beds around the Scilly Isles were begun in 1984 by the Nature Conservancy Council and were continued until 1988. Following a gap of two year, 1988 and 1989, when no studies were carried out a further limited survey was done in 1991 (Fowler & Pilley, 1992). Volunteer groups have since carried out surveys every year from 1992 to 2004 (Raines et al., 1993; Cleator et al., 1996; Mackenzie & Rickards, 1996; Irving et al., Irving and Mackenzie, 1997 and Irving et al., 1998, Cook et al., 2000, Cook et al., 2001, Cook, 2002, 2003and 2004). The initial surveys were only carried out on two sites, English Island, East Higher Town Bay, St. Martin's and at Old Grimsby Harbour on the east side of Tresco. Since then addition sites at East Broad Ledge, St Martin's and West Broad Ledge, Tresco were added and following the investigation of a

7 RoxAnn identified site, a further Zostera bed was surveyed at Little Arthur in the Eastern Isles. To complete the set of beds surveyed, the beds at Rushy Bay, Bryher and Bar Point, St. Mary’s were added in 2000 (Cook et al., 2001).

In addition to the initial concerns relating to the population and concentration of the plants within the beds it was noted in the surveys of the beds between 1988 and 1991 that the plants were infected with the parasitic slime mould of the genus Labrynthula sp. more common known as wasting disease. The infection of the Zostera plants with Labrynthula caused widespread loss in many areas during the 1930s and 1940s including the Isles of Scilly and various other beds in the south-west (den Hartog, 1987). The surveys carried out by the Nature Conservancy Council during the years 1984 to 1988 reported no incidences of Labrynthula within the beds surveyed (Fowler & Pilly, 1992). Although no formal surveys of the beds were carried out in the years 1989 and 1990, Fowler (1992) reported that during the years 1988 to 1991, the health of the beds had shown a marked deterioration. The cause of this was attributed to Labrynthula and this was later confirmed by the Coral Cay Conservation Sub-Aqua Club expedition to the islands in 1992 (Raines et al., 1993).

It is unclear what caused the reoccurrence of the infection in the beds in the Isles of Scillies although Cleator et al. (1996) suggested a worsening in environmental conditions i.e. changed water temperature water flow and sedimentation or even changes in irradiance. Whatever the cause it was thought, however, thought that the increase in occurrence of Labrynthula was due to metabolic stress making the individual Zostera plants more susceptible to infection by reducing the amount of organic compounds involved in the resistance of disease and the growth of epiphytes on the leaves.

The disease first becomes apparent with the appearance of small black spots on the leaves. These then spread along the length of the leaf until the leaf can become so infected that photosynthesis is no longer possible and the leaf dies. If the infection is not severe the plant will remain viable and continue to grow. However, should the infection continue for a number of years the leaf loss may cause the rhizomes to also become infected and cause the plant to die (den Hartog, 1989). This die back has yet to be confirmed in the beds around the Isles of Scilly.

2.01 Aims of the survey The surveys carried out during the 2004 expedition followed on from those undertaken in earlier years and the aims were:

• To assess the plant density of different beds by surveying randomly selected samples. • To count the number of leaves per plant and measure the maximum leaf length. • To assess the amount of Labrynthula infection within the beds. • To assess the amount of epiphytic cover on each plant • To count the number of flowering plants present • To count the number of plants with eggs present on the leaves.

8 2.02 Locations The positions of the central datum marker for the beds surveys during the 2004 survey were obtained using differential GPS.

Site Latitude N Longitude W Date Surveyed Old Grimsby Harbour, Tresco 49 57.618 006 19.779 2nd August Higher Town Bay, St. Martin's 49 57.418 006 16.416 2nd August Broad Ledge, Tresco 49 56.353 006 19.766 4th August West Broad Ledge, St. Martin's 49 57.707 006 18.445 5th August Little Arthur, Eastern Isles 49 56.945 006 15.926 3rd August Bar Point, St. Mary's 49 56.281 006 18.055 6th August Rushy Bay, Bryher 49 56.587 006 21.326 6th August

Table 1 Location of Central Datum Point for survey sites

2.03 Method Two methods were used during the 2004 survey.

• Method A – From central datum marker • Method B – Transect swim along laid marker line

Method A At each site a central line was lowered to the sea floor to act as a datum from which all bearings and distances were measured. The position of this line was chosen by eye to be approximately central in the bed to be surveyed by means of a surface swim over the bed to determine its extent. Care was also taken to ensure that the datum marker was located in a sand patch within the bed to avoid disturbing any plants. Once the central line was positioned, pairs of divers were then sent to take samples from points at randomly selected distances, between 0 and 30m, and bearings, between 0° and 359°, from the central line. At each of the sites, a 0.25m2 quadrat, constructed of a 0.5m by 0.5m square constructed from copper tubing was positioned so that the bottom left hand corner of the quadrat lay against the right hand edge of the tape at the indicated distance.

Figure 2 A Quadrat

9 The bearing was measured using a standard divers compass and the distance from the central line was measured using a marked tape. Once at the indicated position, all the plants within the bottom left hand quarter were then cut above the rhizomes and stored in a marked plastic bag for later analysis. Care was taken to ensure that only the plants with their rhizomes directly under the quarter square were taken by ensuring that all leaves were traced to the base.

Method B This was devised as an alternative way of measuring plant density and also to map in more detail, a part of the Zostera bed. The measurements were taken along a 70m transect which was positioned so that is lay across the bed close to the central datum marker for the survey carried out under method A. The 70m long datum line was deployed from the back of a RIB with weights at each end to ensure constant tension and marker lines to the surface for safety. The line was marked at 1m intervals at which points in situ measurements were made. At each data point a quadrat measuring 0.25m x 0.25m was laid either side of the line such that the bottom corner of the quadrat touched the data point. At each point the following variables were recorded:

• Percentage coverage of quadrat with Zostera marina (see table below) • Number of Sargassum muticum plants in area covered by quadrat

Zostera Marina Cover % Cover Score Under 10 1 10 to 50 2 50 to 80 3 Over 80 4

Table 2 Scoring system for Method B Survey

2.04 Data Analysis For each sample bag taken in a Method A survey, the following variables were recorded:

• Bearing and distance at which sample was taken • Number of plants per bag • Maximum plants length • Amount of Labrynthula infection and percentage number of infected leaves • Amount of Epiphytic cover • Number of flowering plants

10 Amount of Percentage of Score Diagrammatic Representation of Infection Infection Infection

0 Uninfected 0%

Some infection 1 <10% apparent As much as half the leaf 2 10 - 50% infected Over half the leaf 3 50 - 80% infected

Almost all the leaf 4 >80% infected

Table 3 Scoring system for Leaf Infection and Epiphyte cover

The data were initially recorded on a preformatted sheet and then loaded into an Excel spreadsheet for further analysis where the following was calculated:

- The density of plants per 0.0625m2 - One-way Analysis of Variance (ANOV) on maximum leaf length and percentage of infected leaves between the different sites surveyed to examine if any significant difference (with a 95% confidence level) exists between the five sites. - Correlation matrix of the variable listed above to investigate the existence of any relationship between these variables. - Frequency analysis of longest leaf length to investigate the population structure at the five sites.

Figure 3 Diver sampling Zostera (Picture courtesy of Ben Crossett, 2003)

11 2.1 Data Analysis for 2004 The sampling of the seven sites took place during the period 2 to 6 August 2004 from the dive boat EVA. A summary of the results from these surveys appears in table 4.

West Old Higher Broad Little Grimsby Town Broad Ledge, Arthur, Harbour, Bay, St. Ledge, St. Eastern Tresco Martin's Tresco Martins Isles Total Number of Quadrats 24 25 25 25 24 Number of Empty Quadrats 10 9 7 9 2 Total Number of Plants 143 291 210 82 290 Total Number of Leaves 591 1196 804 327 1343 Percentage Leaves Infected 46.9 79.0 75.9 56.2 68.3 Mean Infection Score 0.64 1.00 1.06 0.70 0.82 Mean Epiphyte Score 1.66 1.66 0.13 1.44 1.58 Mean Plant Length (cm) 33.2 47.8 45.4 44.7 69.5 Standard Deviation of plant length 13.46 14.19 16.31 19.95 20.56 Mean Plant Density / 0.0625m2 5.96 11.64 8.40 3.28 12.08 Mean Biomass Index 197.82 556.39 381.36 146.62 839.79 Number of Flowering Plants 0 2 0 0 5 Number of Plants with Eggs 1 1 80 71 14

Percentage of Flowering Plants 0.00 0.69 0.00 0.00 1.72 Percentage of Plants with Eggs 0.70 0.34 38.10 86.59 4.83 Plant Density Ignoring Empties 10.21 18.19 11.67 5.13 13.18 Mean Number of Leaves per Plant 4.13 4.11 3.83 3.99 4.63

Table 4 Summary of Zostera analysis, 2004 survey

Included again this year is reference to the number of null bags recorded at each of the sites surveyed. It is important to include these bags in the density calculation as it reflects the patchy nature of most of the Zostera beds and can highlight the changing condition of the bed such as at Higher Town Bay, St. Martin’s. The highly patchy nature of the Seagrass beds is further illustrated by the Method B survey. The mean density figure however also masks the density of the plants where growth does occur so a second mean plant density figure is included, calculated by ignoring the null bags, for comparison.

12

West Broad Old Grimsby Broad Ledge, Ledge, Higher Town Harbour, Tresco Tresco St.Martin's Bay, St. Martin's LHS RHS LHS RHS LHS RHS LHS RHS 0 53 56 21 17 22 21 26 27 1 4 1 8 15 3 9 7 3 2 1 2 17 16 13 14 4 8 3 7 6 17 11 20 14 14 13 Score Freq.

Zostera Density 4 7 7 5 9 12 12 17 17 Mean Score 0.85 0.78 1.79 1.97 2.36 2.19 2.45 2.47 Plant Density * 4.87 4.51 10.31 11.31 6.50 6.02 25.74 25.94 * Plant Density per 0.0625m2

Table 5 Results of Method B Survey of Zostera Density

The plant density data in Table 6 above is calculated as the product of the Mean Score multiplied by the highest recorded number of plants per 0.0625m2 for each bed; Old Grimsby Harbour (23), Broad Ledge (23), West Broad Ledge (11) and Higher Town Bay (42). This assumption means that the plant densities are higher than those in Method A.

2.11 Bar Point St. Mary’s and Rushy Bay, Bryher No data for Bar Point, St. Mary’s or Rushy Bay, Bryher is included above for the 2004 survey. Rushy Bay was also excluded in the 2003 survey and following the high number of null bags encountered during the 2003 survey leading to a distorted plant density at Bar Point, St. Mary’s, this bed was also excluded. It is hoped that a variation on the method used for the other beds can be employed during the 2005 survey to give a fuller picture of Zostera growth in the Isles of Scilly.

13 2.2 Analysis of Time Series Data

2.21 Leaf Infection

West Old Higher Broad Little Grimsby Town Broad Ledge, Arthur, Bar Rushy Harbour, Bay, St. Ledge, St. Eastern Point, St. Bay, Tresco Martin's Tresco Martin's Isles Mary's Bryher August '04 47 79 76 56 68 n/a n/a July '03 52 69 65 70 73 67 60 August '02 68 53 71 74 63 57 56 August '01 51 65 76 66 86 69 68 August '00 47 56 65 60 58 62 47 August '99 60 67 71 69 52 55 69 August '98 57 67 76 61 65 n/a n/a August '97 43 37 44 49 n/a n/a n/a July '96 69 63 61 n/a n/a n/a n/a June '95 63 42 n/a n/a n/a n/a n/a August '94 56 79 n/a n/a n/a n/a n/a July '93 59 65 n/a n/a n/a n/a n/a

Table 6 Mean percentage number of leaves infected at survey sites

Comparison of 2004 percentage leaf infection data for the beds surveyed with data from pervious years show three beds with a lower percentage than in 2003. Of these, Old Grimsby Harbour has the lowest percent of infected leaves (47) of any bed surveyed which is the lowest recorded at this bed since 2000 while the bed at West Broad Ledge has the lowest amount (56) recorded here since 1997. The third bed with a lower percentage number of leaves infected than in 2003 was at Little Arthur (68). The remaining two beds Higher Town Bay, St. Martin’s (79) and Broad Ledge, Tresco (76) both recorded the equal highest percentage amount of leaves infected since recording began, Higher Town Bay equal with the level in 1994 and Broad Ledge, Tresco equal with 1998.

14 90

80

70

60

50 Percent Infection 40

30 July '93 August June '95 July '96 August August August August August August July '03 August '94 '97 '98 '99 '00 '01 '02 '04

Old Grimsby Harbour, Tresco Higher Town Bay, St. Martin's Broad Ledge, Tresco

West Broad Ledge, St. Martin's Little Arthur, Eastern Isles

Figure 4 Mean percentage number of leaves infected at survey sites

Groups Count Sum Average Variance Old Grimsby Harbour, Tresco 143 67.0 0.47 0.07 Higher Town Bay, St. Martin's 291 230.0 0.79 0.02 Broad Ledge, Tresco 210 159.4 0.76 0.03 West Broad Ledge, St. Martin's 82 46.1 0.56 0.06 Little Arthur, Eastern Isles 290 198.1 0.68 0.03

Analysis of Variation Source of Variation SS df MS F P-value F crit Between Groups 12.31 4 3.08 88.34 2E-64 2.38 Within Groups 35.21 1011 0.03 Total 47.52 1015

Table 7 One-way Analysis of variance of Percentage Leaf Infection

The one-way analysis of variance for the null hypothesis that ‘there is no significant difference in the amount of leaf infection between sites’ shows that this null hypothesis must be rejected, as the calculated F value of 88.34 is greater than the F-Critical value of 2.38. This indicates that there is a significant difference in the amount of infection between beds

15 2.22 Plant Size Distribution and Plant Density The plant size distribution, measured as the length of the longest leaf, is illustrated in figure 6 below. This shows that, as seen in previous years, the distribution is highly different between each site. The distribution for Broad Ledge Tresco has a near normal distribution, those at Old Grimsby Harbour and Higher Town Bay appear to be bi-modal and the bed at West Broad Ledge, St. Martins has a more even distribution of plant lengths. The distribution Little Arthur, Eastern Isles continues to be slewed towards the longer leaf lengths.

West Old Higher Broad Little Grimsby Town Broad Ledge, Arthur, Bar Rushy Harbour, Bay, St. Ledge, St. Eastern Point, St. Bay, Tresco Martin's Tresco Martin's Isles Mary's Bryher August '04 33.2 47.8 45.4 44.7 69.5 n/a n/a July '03 39.1 44.3 40.2 72.6 74.8 45.6 49.3 August '02 43.8 34.8 34.0 55.8 85.6 67.0 55.9 August '01 33.8 41.0 47.4 45.3 69.5 60.6 61.2 August '00 38.9 39.9 32.7 53.3 89.2 46.5 53.0 August '99 37.5 45.8 40.4 64.5 79.0 58.2 66.5 August '98 29.0 50.0 47.0 62.0 86.0 n/a n/a August '97 49.0 48.0 41.0 53.0 n/a n/a n/a July '96 59.0 54.0 40.0 n/a n/a n/a n/a June '95 n/a n/a n/a n/a n/a n/a n/a August '94 56.8 61.0 n/a n/a n/a n/a n/a July '93 69.4 48.8 n/a n/a n/a n/a n/a

Table 8 Maximum leaf lengths (cms) at survey sites

The site with the highest mean maximum plant length (69.5 cms) was once again the bed at Little Arthur in the Eastern Isles though this was again down from the mean lengths (74.8cms) recorded in 2003 and (85.6 cms) in 2002. The site with he lowest mean plant length was again that Old Grimsby Harbour (33.2cms) again down from the mean length (39.1cms) recorded in 2003. The third site with a lower mean plant length than in 2003 was that at West Broad Ledge, St. Martin’s down from the record high 72.6cms in 2003 to a record low for this site, 44.7cms in 2004. The sites at Higher Town Bay, St. Martin’s and Broad Ledge, Tresco both has a small increase in the mean plant length recorded in 2004 from that recorded in 2003, 47.8cms up from 44.3cms and 45.4cms up from 40.2cms respectively.

16 100 90 80 70 60 50 40 30 20 Maximum Leaf Length (cm) 10 0 July '96 August August August August August August July '03 August '97 '98 '99 '00 '01 '02 '04

Old Grimsby Harbour, Tresco Highe r To wn B a y, S t. M a rtin's Broad Ledge, Tresco We s t B ro a d Le dge , S t. M a rtin's Little Arthur, Eastern Isles

Figure 5 Maximum leaf lengths at survey sites

Groups Count Sum Average Variance Old Grimsby Harbour, Tresco 143 4754 33.24 181.23 Higher Town Bay, St. Martin's 291 13900 47.77 201.42 Broad Ledge, Tresco 210 9524 45.35 266.05 West Broad Ledge, St. Martin's 82 3669 44.74 398.00 Little Arthur, Eastern Isles 290 20167 69.54 422.66

Analysis of Variation Source of Variation SS df MS F P-value F crit Between Groups 157689 4 39422.33 135.50 1E-92 2.38 Within Groups 294136 1011 290.94 Total 451825 1015

Table 9 One-way Analysis of variance of Maximum Leaf Length

From table 9 it can be seen that the Null Hypothesis that ‘no significant difference existed between the leaf length from plants at the five sites’ is not supported with the F value of 135.50 being larger than the F-Critical value of 2.38 supporting the evidence above that the distributions are markedly different.

17 50 45 40 35 30 er

mb 25 Nu 20 15 10 5 0 0 20406080100120140 Maximum Leaf Length (cm)

Old Grimsby Harbour, Tresco Higher Town Bay, St. Martin's Broad Ledge, Tresco West Broad Ledge, St. Martins Little Arthur, Eastern Isles

Figure 6 Distribution of maximum leaf lengths at survey sites.

18 2.23 Mean Plant Density

West Old Higher Broad Little Grimsby Town Broad Ledge, Arthur, Bar Rushy Harbour, Bay, St. Ledge, St. Eastern Point, St. Bay, Tresco Martin's Tresco Martin's Isles Mary's Bryher August '04 5.96 11.64 8.40 3.28 12.08 n/a n/a July '03 7.37 9.90 9.73 4.80 11.19 1.83 n/a August '02 4.83 7.21 11.10 1.96 11.60 6.04 3.16 August '01 5.44 12.24 7.80 4.72 8.76 5.76 5.04 August '00 2.48 11.44 10.40 4.92 9.50 4.00 2.32 August '99 3.62 10.20 9.17 5.12 9.84 7.39 4.59 August '98 7.32 14.08 4.20 7.36 8.28 n/a n/a August '97 6.78 11.79 4.83 9.52 n/a n/a n/a July '96 7.17 15.96 7.50 n/a n/a n/a n/a June '95 n/a n/a n/a n/a n/a n/a n/a August '94 8.83 9.64 n/a n/a n/a n/a n/a July '93 4.05 5.45 n/a n/a n/a n/a n/a

Table 10 Mean Plant Density per 0.0625m2 at survey sites

18 16 14 12 10 8 6 Plant density 4 2 0

6 7 8 9 0 1 2 3 4 '9 '9 '9 '9 '0 '0 '0 '0 '0 t t t t t t t y s s s s s s y s l u u u u u u l u Ju g g g g g g Ju g u u u u u u u A A A A A A A

Old Grimsby Harbour, Tresco Higher Town Bay, St. Martin's Broad Ledge, Tresco

West Broad Ledge, St. Martin's Little Arthur, Eastern Isles

Figure 7 Mean Plant Density per 0.0625m2 at survey sites

19 Two beds had a higher mean plant density in 2004 than in 2003 with the bed at Little Arthur recording its highest ever mean number of plants, 12.08, up nearly 1 plant over that in 2003. The increase at the other bed at Higher Town Bay was even higher, up 1.74 from 9.90 plants to 11.64 plants. The remaining three beds all had lower mean plant densities in 2004 than in 2003 though the only bed that might be of concern is that at West Broad Ledge, St. martin’s, down 1.52 plants from 4.80 in 2003 to 3.28 in 2004. This was also the biggest fall in plant densities of any of the three beds with a lower plant density.

2.24 Mean Biomass Index

West Old Higher Broad Little Grimsby Town Broad Ledge, Arthur, Bar Rushy Harbour, Bay, St. Ledge, St. Eastern Point, St. Bay, Tresco Martin's Tresco Martin's Isles Mary's Bryher August '04 197.9 556.4 381.4 146.6 839.6 n/a n/a July '03 288.2 438.6 391.1 348.5 837.0 83.4 n/a August '02 211.6 250.9 377.4 109.4 993.0 404.7 176.6 August '01 183.7 501.3 369.8 214.0 608.9 349.2 308.5 August '00 96.5 456.5 340.1 262.1 847.4 186.0 123.0 August '99 135.6 467.2 371.0 329.9 777.4 430.0 305.1 August '98 212.3 704.0 197.4 456.3 712.1 n/a n/a August '97 332.2 565.9 198.0 504.6 n/a n/a n/a July '96 423.0 861.8 300.0 n/a n/a n/a n/a June '95 n/a n/a n/a n/a n/a n/a n/a August '94 501.5 588.0 n/a n/a n/a n/a n/a July '93 281.1 266.0 n/a n/a n/a n/a n/a

Table 11 Mean Biomass index at main survey sites

20 1200.0

1000.0

800.0

600.0

Biomas Index 400.0

200.0

0.0 July August August August August August August July August '96 '97 '98 '99 '00 '01 '02 '03 '04

Old Grimsby Harbour, Tresco H ighe r T o wn B a y, S t. M a rtin's Broad Ledge, Tresco We s t B ro a d Le dg e , S t. M a rtin 's Little Arthur, Eastern Isles

Figure 8 Mean Biomass index at main survey sites

The bed with the highest mean biomass index was again that at Little Arthur in the Eastern Isles (839.6), only 2.6 higher than in 2003. The bed at Higher Town Bay had the next highest level and at 556.4 was over 100 higher than in 2003 and is the highest level recorded at this bed since 1998. Of the three beds that had a fall in mean biomass index, Broad Ledge Tresco was only slightly lower than in 2003, Old Grimsby Harbour was also lower with the bed at West Broad Ledge having the lowest Mean Biomass index at 146.6, over half that recorded in 2003 but not as low as was recorded in 2002 (109.4).

2.3 Individual Bed Reports

2.31 Old Grimsby Harbour, Tresco

The bed lies along the southern edge of the natural harbour formed by the small bay on the eastern side of Tresco that forms one of the main access points to the island from the sea. Although this access is dependant on the state of the tide, a large number of boats use the stone quay situated in the centre of the western side of the bay. The bay is found on the eastern side of the island and it provides shelter for both the visiting boats that anchor on the edge of the bay and local boats that use the permanent mooring buoys in the bay, from the prevailing south westerly winds. As a result of the large tidal range experienced throughout the whole of the Scillies, large areas of the bay are exposed at low water. This includes the southern edge of the Zostera bed which lies close to one of the beaches used by visiting tourists. Here, the water depth along the southern edge of the Zostera bed is shallow enough to allow trampling of the plants. Cook et al. (2001), Cook 2002, 2003

21 and 2004 described the highly patchy nature of the bed at this location. It was suggested that the movement of the mooring chains might be one factor. These moorings are anchored to base weight by means of a heavy sinker chain with a large buoy on the surface. The chains have to be long enough to allow for the rise and fall of the tide, which means that at low water there is a large amount of chain lying on the sea floor and over the Zostera plants. As the direction of the wind changes the moorings move round causing the chains to be dragged over the plants. This can cause plants to be dislodged and even for the rhizomes to be damaged. The presence of exposed and dislodged rhizomes within the arc of the chains movement help to confirm this theory. Although Cook et al. (2001) did not find any direct correlation between the position of the buoys and the patches it was suggested that this was possibly due to the extreme patchiness of the bed and the overall low plant density during the 2000 survey. Surface swims during the 2001 (Cook, 2002) and 2002 (Cook, 2003) surveys plant densities were higher, confirmed the continued patchy nature of the growth. This was further confirmed by the transect survey introduced by Cook during the 2003 survey (Cook, 2004). The correlation of the patches with the positions of the mooring chains described by Cook (2002) was again noted during the 2004 survey with the rhizomes forming the bed in the swinging range of the chain having been removed.

Since the warning issued in the report of the survey of this Zostera bed in 2000 (Cook et al., 2001) due to the decline in plant density to a low of 2.48 plants per 0.0625m2, the bed has recovered. Further evidence of this recovery was recorded during the 2003 survey with a mean plant density of 7.37 plants per 0.0625m2, the highest level recorded since August 1994 and although the mean plant density was slightly down from this high, 5.96 plants per 0.0625m2, the bed appears to be in good health. However as has been noted in several previous reports the bed here remains highly patchy. In order to get a better picture of the distribution it was decided to conduct a method B transect survey across the bed in addition to the usual 25 sample points in method A. Both these surveys confirmed the still patchy nature of this bed and the data from both are shown in Figure 9 below. The amount of infection in the leaves, as recorded by the mean percentage number of infected leaves, was the lowest recorded at any site during the 2004 survey and the average infection score at 0.64 was also the lowest for 2004. Conversely, the mean epiphyte score of 1.66 was the joint highest recorded in 2004.

The seabed at Old Grimsby Harbour was described by Cook (2003) as being mainly medium sand overlaid with the Zostera intermixed with some over lying loose macro algae. This was confirmed by the transect survey where all the survey points recorded sand. No Sargassum was noted on any of the survey swims though this is probably due the lack of any suitable holdfasts being present as Sargassum is present in several other locations around Tresco.

The transect swim during the 2004 survey showed no change in the condition of the seabed.

22 Plant Density Plot, Old Grimsby Harbour, 2004 N 50 Colour Scale 0 1 2 3 40 4 5 6 7 8 9 30 10 11 12 13 14 15 20 16 17 18 19 20 21 W 10 E 22 23 24 25 26 27 0 28 29 30 -40-30-20-100 10203040 31 32 33 -10 34 35 36 37 38 39 40 -20 41 42 43 44 45 -30 S Figure 9 Location of sample points and individual plant densities, Old Grimsby Harbour

2.32 Higher Town Bay, St. Martin’s

The bay is situated on the southern edge of St. Martin’s and is bounded by Cruther’s Point to the west and English Point to the east. At the western end of the bay is a small stone harbour which acts as one of the main access points to the island from the sea. The bay is also used as an anchorage for a number of small vessels and the fringing beach and dune system are a popular destination for tourists. The Zostera bed lies at the eastern end of the bay and runs from English Island along the edge of the bay. Strong tidal streams flow across the bay and the bed is also exposed to the prevailing south-westerly winds. The sea floor here is comprised of medium sands which, given the strong tidal streams, is liable to erosion. This sediment movement and erosion is prevented in some places however by the Zostera rhizomes that help bind the sand and also promote accretion to the extent that the Zostera forms prominent platforms that stand up to 10cm above the surrounding sea floor. The strong tidal streams bring large fronds of loose macro algae from the rocky ground of the eastern isles and although there are very few other species growing here, there are large loose fronds of transported material that overlie the Zostera. The bed at Higher Town Bay is highly patchy in nature but where the Zostera rhizomes are well established the plant density is high. In order to obtain a better picture of this bed

23 a method B transect was also carried out. The results of these surveys are displayed in Figure 10 below.

Plant Density Plot, Higher Town Bay, St. Martin's, 2004 N Colour Scale 30 0 1 2 3 4 5 20 6 7 8 9 10 11 10 12 13 14 15 16 E 17 W 18 0 19 20 -40 -30 -20 -10 0 10 20 30 21 22 23 24 -10 25 26 27 28 29 30 -20 31 32 33 34 35 36 37 -3 0 38 39 40 41 42 43 -40 44 45 S Figure 10 Location of sample points and individual plant density, Higher Town Bay

The mean plant density was 11.64 plants per 0.0625m2 which although up on the density in 2003, is down if null bags are ignored. The increase in plant density from 2003 is again in sharp contrast to the amount of infection recorded. This bed had the highest percentage number of leaves infected (79% compared with 69% in 2003), a mean infection score of 1.0 (0.91 in 2003) and mean epiphyte cover score of 1.66, equal highest of any bed. The figure of 79.0 percent of leaves infected equals the highest percentage infection figure recorded in 1994.

The seabed, as recorded in the Method B transect swim, showed a mix of sand and coarser material, mainly small gravel, though only one Sargassum plant was noted. It is possible that the strength of the tide across the bed washes most of the Sargassum plants off the site given that any suitable holdfast is not enough to maintain a stationary position.

Examination of the edge of the Zostera platforms again showed exposed rhizomes and some obvious signs of erosion. The edges of the platforms are open to a variety of forces

24 which might lead their reduction and although the reasons for this erosion and hence reduction in the area of the bed are not clear though there are several possible reasons.

• The strong tidal streams that flow across the bay may erode the base of the platform and cause the collapse of the overlying rhizome system. • The bed is the shallowest of all those found in the Scillies, it drys at low water springs and as it is exposed to the south-westerly winds, wave action will erode the edges of the bed. • The proximity of the bed to the beach and the shallowness of the bed mean that it is liable to trampling, however this is not thought to be a major problem. As mentioned above, the small harbour at the western end of the bay is used as an access point to the island and is used by several boats, including those transporting divers to and from their dive sites. During the survey of the bed during the 2002 expedition, one of these boats was observed attempting to gain access to the harbour across the western edge of the bed. As this was close to low water, the water over the bed was too shallow to allow the stern of the boat to travel across the bed and the boat ground on the bed. To overcome this, the passengers on the boat climbed onto the bow of the boat and then, with the stern partially lifted, the boat, at full power, ploughed through the bed into deeper water. Zostera plants were observed being ripped from the bed. Though this practice was not observed in 2004 it has been reported that it is not uncommon at spring tides.

2.33 Broad Ledge, Tresco Broad Ledge lies on the southern edge of Tresco and together with Crab Ledge, Tabaccoman’s Ledge and Green Island to the east, forms part of the large inter tidal area that fringes the southern coast of Tresco. There is a small jetty that allows access to the island from the sea and is used by tourist boats when the tides allows. The bay is used on an occasional basis as and anchoring point for smaller yachts. The area is open to the prevailing south-westerly winds and weak tidal streams. The seabed here is comprised of coarse sand, mixed with small gravel, pebbles and some cobbles and some Sargassum muticum plants and small macro algae can be founds attached to the small material. Despite the presence of the macro algae, the Zostera bed here is extensive and competes well with the other species.

The plant density, as recorded by from the random sample point survey was 8.40 plants per 0.0625m2, slightly down when compared with 9.73 plants per 0.0625m2 in 2003. The mean percentage leaf infection rose to 75.9%, up from 65% in 2003 and the mean leaf infection score also rose to 1.06, the highest at any bed in 2004, from 0.95. The most remarkable feature of the Zostera growth at this bed was the lack of epiphyte cover on the leaves. The mean epiphyte cover score was 0.13. over 1.3 lower than the next highest score. The seabed comprised of sand with ‘one or two small stones’ to which was attached a Sargassum plant was attached.

25 Plant Density Plot, Broad Ledge, Tresco, 2004 N 50 Colour Scale 0 1 2 40 3 4 5 6 7 8 30 9 10 11 12 13 14 20 15 16 17 18 19 20 21 10 22 23 24 W E 25 26 27 0 28 29 -30 -20 -10 0 10 20 30 40 50 30 31 32 33 -10 34 35 36 37 38 39 -20 40 41 42 43 44 -30 45 S Figure 11 Location of sample points and individual plant density, Broad Ledge

2.34 West Broad Ledge, St Martin’s

West Broad Ledge lies on the south-western edge of St. Martin’s and on the southern edge of the channel between St. Martin’s and Tean. This channel is used by pleasure boats navigating between the islands but not often as an anchoring point as boats generally choosing to anchor further to the north off the access jetty. The seabed is comprised of medium and coarse sand with small gravel and pebbles on which some fronds of Sargassum and other species of small macro algae were noted. The Zostera bed covers a wide area but is highly patchy in nature.

Following the 2002 survey, Cook (2003) reported that the mean plant density had fallen every year since recording began at this site in 1997, from 9.52 plants per 0.0625m2 to 1.96 plants per 0.0625m2 in 2002. At this stage, the bed was in danger of declining to the point where was in danger of disappearing altogether. In 2003, the plant density had recovered to 4.80 plants per 0.0625m2 though fell slightly to 3.28 in 2004 plants per 0.0625m2.The reasons for the decline in density from 1997 are not clear. The bed, though swept by currents does not suffer from the anchor or mooring chain damage seen at Old Grimsby Harbour, Tresco. It has one of the lower mean percentage number of leaves infected, 56.2%, much reduced from the 70% in 2003 and the mean infection score was

26 also down to 0.82 from 0.95 in 2003. As with the majority of the beds the epiphyte cover was high with a mean cover score of 1.44 (2003) stated that the reason for the fall in density was not clear and this is still the case. In 2002 the mean percentage plant infection was 74%, the highest recorded at this site, and in 2003 although down slightly at 70%, was still high. The mean leaf infection score also fell slightly from 1.00 in 2002 to 0.95.

As recorded above the seabed is comprised of mainly sand but with some larger material. The presence of the better holdfasts resulted in 4 Sargassum plants being recorded during the transect swim across the bed, the results of which are shown in figure 10 below. This transect swim also confirms the highly patchy nature of this bed.

Plant Density Plot, West Broad Ledge, 2004 N 40 Colour Scale 0 1 2 3 30 4 5 6 7 8 9 20 10 11 12 13 14 15 10 16 17 18 19 20 21 0 22

W E 23 24 -40 -30 -20 -10 0 10 20 30 40 25 26 27 28 -10 29 30 31 32 33 34 -20 35 36 37 38 39 40 -30 41 42 43 44 45 -40 S Figure 12 Location of sample points and individual plant density, West Broad Ledge

2.35 Little Arthur, Eastern Isles This bed lies in the eastern isles and to the east of Little Arthur where it is sheltered from the prevailing south-westerly winds and strong currents that flow round the islands. The eastern isles are also home to a colony of grey seals which attract several boats of tourists who come to view them. Few of these boats however anchor here and impact the Zostera bed. The majority of the substrate within the islands is comprised of bedrock and large

27 boulders which are covered by dense growths of macro algae. The Zostera patch, however, lies in a small patch of medium sand. Despite the large amount of surrounding macro algae, the Zostera bed is relatively free from any covering plants. This is one of the deepest beds surveyed in the islands and although small in area, exists as a complete single bed with few patches.

Plant Density Plot, Higher Town Bay, St. Martin's, 2004 N Colour Scale 30 0 1 2 3 4 5 20 6 7 8 9 10 11 10 12 13 14 15 16 E 17 W 18 0 19 20 -40 -30 -20 -10 0 10 20 30 21 22 23 24 -10 25 26 27 28 29 30 -20 31 32 33 34 35 36 37 -3 0 38 39 40 41 42 43 -40 44 45 S Figure 13 Location of sample points and individual plant density, Little Arthur

As noted above, this bed is unique within the Scillies in that it is well defined, being confined by the geology of the area and exists as a near complete bed with only a few small bare patches. The mean plant density recorded at this site during the 2003 survey was again the highest recorded at any site, 12.08 plants per 0.0625m2 up from 11.19 plants per 0.0625m2, and a record density for this bed. The mean percentage number of leaves infected was 68.3% down from 73% in 2003 while the mean infection score was 0.82 down from 0.91in 2003 and the same as in 2002. The mean epiphyte score was again high at 1.58.

28 2.4 Discussion and Future Work

The 2004 survey of the Isle of Scilly Zostera marina beds developed the work begun in earlier years and despite the fact that three of the five beds surveyed during 2004 had lower mean plant densities than in 2003, the five beds appear to remain in good health The addition of the more detailed transect dives across some of the beds introduced last years gives a better picture of the distribution of the Zostera within the beds and has helped to revealed the consistent feature of all the Zostera beds in the Scillies, with the exception of the bed at Little Arthur in the Eastern Isles, the is the patchiness of their distribution.

Anthropogenic effects have been suggested for this and some have been identified. The swinging mooring chains at Old Grimsby Harbour, Tresco and the use of the Zostera bed at Higher Town Bay, St. Martin’s as a shallow water passage to the local harbour both of which have had an observable adverse impact on the respective beds. Despite this, however, the amount of Zostera in the five main beds surveyed appears to have increased from 2003 and the bed at Old Grimsby Harbour, that gave such cause for concern in 2000, has now recovered. Plant densities also improved at two other beds, were similar at another but down again at Broad Ledge, Tresco. The reasons for this net improvement in overall densities are not clear. The percentage amount of leaves infected has not reduced to any great extent and the amount of infection in the leaves is only slightly down from that in 2003. The general condition of the leaves appeared, conversely to be reduced with much higher levels of epiphyte cover than seen before. With the exception of Broad Ledge, Treso which had very low levels, the beds all had epiphyte cover scores over 1.0. Again the reasons for this are not clear. There is no data on the amount of nutrients or pollutants in the water and no detailed data exists for the light levels experienced in the beds over the year.

For the second year there was a reduction in the number of beds surveyed fully in 2004. Rushy Bay was not surveyed in 2003 as amount of Zostera in the small bed was so low as to make a standard survey unworkable. In addition to this the bed at Bar Point, St. Mary’s was also not surveyed in 2004. It was suggested that a smaller radius survey be undertaken to reduce the number of null bags that distort the density data.. Due to lack of resources, it was decided not to survey the bed at all and concentrate on the other beds. However, with a bigger team, both beds could be surveyed, using a Method B transect swim to better map their extent. A bigger team would allow all beds to be more thoroughly mapped.

The amount of infection recorded in the 2003 survey was consistent with the amounts recorded in previous surveys with variations within the individual beds. Statistical analysis of these data suggests that they are significantly different as are the maximum leaf length. The reasons of these differences are still not clear though as has been suggested in previous survey reports the environmental factors are probably important. As has been suggested in previous reports, it is recommended that environmental factors be monitored and more regular sampling of the Zostera is undertaken.

29 3.0 REFERENCES

Cleator, B. 1993. The Status of the genus Zostera in Scottish coastal waters. (Contractor: B. Cleator, Edinburgh). SNH Review No. 22. Edinburgh, Scottish Natural Heritage.

Cleator, B., Nunny, R. and Mackenzie, G., 1996. Coral Cay Conservation Sub-Aqua Club Isles of Scilly 1993 Expedition Report. Coral Cay Conservation Sub-Aqua Club, London.

Cook, K., 2000. Report on the Coral Cay Conservation Sub-Aqua Club 1999 Expedition to the Isles of Scilly.

Cook, K., 2002. Isles of Scilly Zostera marina monitoring 2001 Expedition Report.

Cook, K., 2003. Isles of Scilly Zostera marina monitoring 2002 Expedition Report.

Cook, K., 2004. Isles of Scilly Zostera marina monitoring 2003 Expedition Report.

Cook, K.J., Enderson, A., Reid, T., 1999. Report on the Coral Cay Conservation Sub- Aqua Club 1998 Expedition to the Isles of Scilly.

Cook, K.J., Hinton, C., Reid, T.J., 2001. Report on the Coral Cay Conservation Sub- Aqua Club 2000 Expedition to the Isles of Scilly. den Hartog, C., 1987. ‘Wasting disease’ and other dynamic phenomena in eelgrass Zostera beds. Aquatic Botany, 27: 3-14. den Hartog, C., 1989. Early records of ‘wasting disease’ like damage in eelgrass Zostera marina. Dis. Aquat. Org., 7: 223-226.

Fowler, J. and Cohen, L., 1994. Practical Statistics for Field Biology. John Wiley and Sons, Chichester.

Fowler, S.L., 1992. Marine monitoring in the Isles of Scilly, 1991. Report to the Nature Conservancy Council. 31pp.

Grassle, J. F., and J. P. Grassle, 1978. Life histories and genetic variation in marine invertebrates, in Marine Organisms. Edited by B. Battaglia and J. Beardmore, pp. 347- 364, Plenum, New York.

IGC, 1996 [Online] Marine Protected Areas. Available from http://www.igc.apc.org/habitat/treaties.mar-prot.html.

Irving, R.A., Gibb, J. and Mackenzie, G. 1996. Coral Cay Conservation Sub-Aqua Club Isles of Scilly 1995 Expedition Report. Coral Cay Conservation Sub-Aqua Club, London.

30 Irving, R.A. and Mackenzie, G. 1997. Coral Cay Conservation Sub-Aqua Club Isles of Scilly 1996 Expedition Report. Coral Cay Conservation Sub-Aqua Club, London.

Irving, R.A., Mackenzie, G. and Reid, T., 1998. Report of the Coral Cay Conservation Sub-Aqua Club Isles of Scilly 1997 Expedition to the Isles of Scilly, 1 August - 16 August 1997. Coral Cay Conservation Sub-Aqua Club, London.

Mackenzie, G. and Rickards, K., 1996. Coral Cay Conservation Sub-Aqua Club Isles of Scilly 1994 Expedition Report. Coral Cay Conservation Sub-Aqua Club, London

Raines, P., Nunny, R. and Cleator, B., 1993. Coral Cay Conservation Sub-Aqua Club Isles of Scilly 1992 Expedition Report. Coral Cay Conservation Sub-Aqua Club, London

31