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Date L:..JLr....J^ OYSTER COMMUNITIES ON THE CENTRAL COAST
OF NEW SOUTH WALES
BY
Khin Nyunt
A thesis submitted to the University of New South Wales for the degree of Master of Science.
1976. UNIVERSITY OF N.S.W.
r 16778 -3.AUG.77
LIBRARY This is to certify that the work presented in this thesis has not been submitted for a higher degree to any other University or Institution.
Khin Nyunt. TABLE OF CONTENTS
PAGE
1.0 Introduction 1
2.0 Description of Areas and Stations 9
^ 2.1 Wallis Lake 9
2.2 Sydney Harbour 13 •
2.3 Jervis Bay 15
3.0 Methods 16
3.1 Sampling 16
3.2 Analysis 20
»3.3 Hydrological Survey 22
4.0 • Results and Discussion 22
4.1 Environmental parameters for the 26 * three localities
4.2 Species composition of oyster communities 37
4.3 Similarities between communities 39
4.4 Associations between species 50
4.5 Substrate and latitudinal effects on 57^ oyster communities
, 4.6 Effects of the age of the community and 71 of water flow or oyster communities
' 4.7 Effect of salinity on oyster communities 77
4.8 Effect of season on oyster communities 84
5.0 Summary and Conclusions 91
6.0 Literature Cited 93 ABSTRACT
Oyster communities from Wallis Lake, Sydney Harbour and Jervis Bay were studied and quantitative analyses made to determine the effects of latitude, substrate, age, salinity and season on the density and diversity of the communities.
Mathematical and statistical criteria showed oyster communities to be influenced by the type of substrate such that density and diversity were greatest in rock oyster communities, next for oysters on mangrove pneumatophores and least in the oyster rack communities. It was also shown that the communities at the most northern locality had the greatest species diversity and that diversity is greater in communities in slow moving water than in those from fast moving water. The oysters from the most southern body weight to shell weight ratio than did those from the more northern areas. Similarly those from slow moving water were of a larger size than those from fast moving water. Finally oysters from localities exposed to salinity variations support denser but less diverse communities than oysters from localities of constant salinity. Associations of species in oyster beds were studied by means of the coefficient of association and Mountford's index. It was shown that most of the positive associations of species in oyster beds are due to their similar microhabitat requirements rather than predator/ prey relationships. Seasonal variation in oyster communities was studied at the most northern locality. The diversity and density of the communities showed little cyclic change but winter oysters were of greater length and had a lower body weight to shell weight ratio than summer oysters. ACKNOWLEDGMENT.
I wish to express my grateful thanks to Professor A.K. O'Gower for his encouragement and general advice without which the study would not have been possible. Much help and encouragement has been supplied by staff members of the School of Zoology, especially Mrs. P.I. Dixon. To all those people thanks are rendered. Thanks are also due to the curators of The Australian Museum: Dr. W.F. Ponder (Molluscs); Dr. P.A. Hutchings (Annelids); Dr. D.J.G. Griffin (Crabs); Dr. D. Hoese (Fish) Miss E.C. Pope (Barnacles);and Miss H. Fisher. (Amphipods) who helped in identifying the respective organisms. This study was carried out under the Colombo plan scholarship granted by Commonwealth Education Department Officials who were very helpful and co-operative 1.0 Introduction
Although it is a new branch of scientific study man has dealt with and developed knowledge of Community
Ecology from the beginning of history. Dice (1952) stated
"Ever since Homo sapiens was evolved he must have noted that many kinds of animals and plants are restricted to particular types of habitat, for his very life depended upon a knowledge of where to find his food and where to be on the lookout for dangerous beasts".
"Animals migrat to where cleaner water and greener grass exist" (Old Burmese Proverb). These few words show that primitive man had a considerable knowledge of community ecology. He probably noticed trends in migrations, the environmental factors limiting distribution and abundance of animals, such as food and water, and probably also trophic structures in animal communities.
However, the modern study of ecology started a little over a century ago (Humboldt, 1805; Grisebach, 1838;
Mobius, 1877). The first zoologist to study an animal community was Karl Mobius (1883) who described the community occupying an oyster bank. Mobius proposed the term
"biocoenosis", appreciating that communities are self regulating units.
This thesis deals with the faunal communities inhabiting intertidal oyster shells in different environments and localities on the New South Wales coast (Wallis Lake,
Sydney Harbour and Jervis Bay), Since oysters have long been of economic importance, there are many early investigations on some ecological aspects of oysters. Hopkins (1957) has reviewed these early studies (Brooks,
1891; Dean, 1890; Gilbert, 1899; Grave, 1905; Moore,
1910) in his annotated bibliography on the ecology of oysters.
Studies on the communities of oyster beds have been made by Caspu (1950), Fleming (1952), Frey (1946),
Hughes and Thomas (1971), Korringa (1951), Mattox (1949),
Mistakidis (1957), MacDonald (1940), Pearse and Wharton
(1938), Stephenson and Stephenson (1952), Wells (1961), but many other studies (e.g. Menzel and Hopkins, 1954;
Menzel and Nichy, 1958; Nichy, 1956; McDermott, 1960) were only concerned with the predators and enemies of oysters.
There are 11 species of edible oysters along the
Australian coast (Thomson, 1953), but only the species
Saooostrea cuocullata commeroialis (Iredale and Roughley,
1933) is of any real economic importance. These oysters are generally known as the Sydney Rock Oyster and are found abundantly in the intertidal zone of sheltered rocky shores in New South Wales and are mostly cultivated in estuarine lakes and rivers. This industry now reaps the benefit from a $4 million annual production (Malcolm,
1971) .
While there have been many important reports on the oysters of Australian and adjacent waters (Cox, 1883;
Cranfield, 1968; Fleming, 1952; Iredale and Roughly, 1933,
Roughley 1922, 1926, 1928, 1933; Thomson, 1951, 1952, 1954) only Fleming (1952) has described the community of the oyster bed from Foveaux Strait. Fleming (1952) and other workers on oyster communities have been primarily concerned with the distribution and abundance of organisms (both animals and plants) in the area of the oyster bed. Almost all these workers just listed the species found near and among oyster shells, but did not make any quantitative attempt
to analyse the oyster community. I have found only one recent paper on an oyster community (Hughes and Thomas,
1971) in which a computer was used for community analysis, but the authors were concerned only with the classification of the communities.
Many studies on estuarine and rock communities in Australian waters have been limited to studies on distributions and zonation of species (Bennett and Pope,
1953; Endean et al., 1956; Guiler, 1960; MacIntyre, 1959).
However, Meyer and O'Gower (1963), O'Gower and Meyer
(1964, 1971) made association analysis on densities of six gastropod molluscs of the Sydney Rock platform
communities; and Stephenson and Williams (1971) attempted ordination analysis on.the benthos communities at Sek
Harbour, New Guinea and Moreton Bay (Stephenson et al,,
(1970).
Of the many quantitative analyses employed in
studies of animal and plant communities, ordination analysis
using various indices of similarity seem to be unreliable,
since these methods are based on absence and presence of
species. Nevertheless, ordination analysis presents
graphic structure of the relationships between communities
or between sites studied, and hence the relative importance of known, different, environmental factors may be assessed.
Ordination analysis therefore has been frequently used by many ecologists for animal and plant community studies
(Davis, 1963; Hughes and Thomas, 1971; Kontkaneu, 1957;
Loya, 1972; Stephenson and Williams, 1971; Whittaker and
Fairbanks, 1958).
The determination of species diversity is one of the major criteria used by ecologists in describing a community and species diversity is most simply measured by counting species. However, the discovery that the logrithmic series showed a very close fit to the observed frequency distribution of species of insects having different numbers of individuals in a random sample prompted.
Fisher et at. (1943) to propose the index of diversity a.
Since then several indices of diversity have been suggested.
Some of these indices are based on a theoretical relationship between the number of species and individuals in a sample (Preston, 194 8; Simpson, 1949; MacArthur,
1957; Mcintosh, 1967), while some indices are derived from information theory CBrillouin, 1960; Shannon and
Weaver, 1963).
Indices of diversity based on information theory have recently been widely used in community ecological studies (Buzas and Gibson, 19 69; Kohn, 196 8; Loya, 1972;
Monk, 1967; Sager and Hasler, 1969 etc.), but these indices still have drawbacks, Brillouin's (1960) information units is based on the true population value of each species, which is too large to be counted in most natural communities, while in the Shannon and Weaver's (1963) formula, the proportions of species present are used. Although one can usually
draw a random sample from the parent population, this may
not be feasible when a population of sessile organisms is
arranged in a patchy manner (Pielou, 1966b).
Simpson's (1949) diversity index may also be preferrably used for many community studies, but this
index is very dependent on the numbers of the few more
abundant species, and takes little account of rarer species, which, in most natural populations make up a very considerable portion of the total species suite (Williams,
1964). While these various indices may have ardent
followers, studies by Loya (1972) on corals have shown all
these indices to have the same order of diversity,
irrespective of the magnitudes of the indices.
While indices of diversity relate the numbers of
species to the numbers of individuals in a community they do not indicate whether the community is dominated by a
few species having many individuals, or dominated by many species have a moderate number of individuals. The indices of dominance (O'Gower and Wacasey, 1967; Whittaker, 1965) and of uniformity (Dahl, 1960) are two such indices which relate the numbers of both species and individuals, but also indicate the degree of dominance, but index of uniformity does not adequately describe the community studies (O'Gower and Wacasey, 1967).
Association analysis between the densities of various species and selected, environmental factors has been used by Meyer and O'Gower C1963), O'Gower and Meyer
(1964, 1971) and O'Gower and Wacasey (1967) in their studies on rock platform and estuarine communities. These authors used the chi-square test in association analysis as the environmental factors studies could be expressed in a gradient, but in the case of different factors lacking a gradient, the analysis of variance test is to be preferred, especially as the Potest can analyse the effect of two environmental factors at a time. However, as both indices and association analysis deal with the number of both species and of individuals they are preferable in the statistical sense to analysis of variance tests in community studies, whereas analysis of variance is more applicable to the study of single populations.
In this present study, qualitative analysis of communities were made using ordination analysis (Stephenson and Williams, 1970 diversity index (Fisher et al,, 1943), index of dominance CO'Gower and Wacasey, 1967) and index of similarity (Fager, 1963; Jaccard, 1912; Sorensen, 1948; and Webb, 1950) were used wherever possible for describing the communities while the F-test was used to determine the association between the density of individual species with environmental factors.
Physical, environmental factors, such as temperature, salinity, substratum, current, etc., play an important role in the distribution and abundance of aquatic organisms (Moore, 1958). Latitudinal gradients determine the composition of animal communities along the Australian coast (Bennett and Pope, 1953; Guiler, 1960) and the seasonal fluctuation of species populations change the community structure to a large extent at different times (Elton, 1927; O'Gower and Meyer, 1964). The primary interest of this study therefore was to determine the effects of latitudinal temperature, substrate, water current, salinity and seasonal temperature on the structure of oyster communities. The increase in complexity of the community associated with the increase in its age was also examined.
Consequently sampling of oysters was planned to sample these variations in environmental factors.
This study was made at three localities (Jervis
Bay, Sydney Harbour and Wallis Lake) in the same biological zone (Bennett and Pope, 1953) having different mean sea temperatures (Guiler, 1960), At the two localities at the extremes of the range, oyster communities were sampled on rocks, in the mangrove pneumatophores, and on oyster racks to determine the effects of substrate on the community structure, while in Middle Harbour in Port Jackson the three sampling sites were selected to indicate the probable effects of variation in salinity on community structure, the substratum being similar at three sites. The effect of water current and age on the oyster communities of Wallis
Lake was studied by sampling these communities on oyster racks of differing ages in fast and slower, flowing water.
The oyster community on an abandoned oyster rack was sampled seasonally in 1972 and 1973 to determine the effects of seasonal variations in temperature on the structure of the oyster community. Wallis Lake
Sydney
Jervis Bay
Figure 1. Location of the three sampling areas in New South Wales 2.0 Description of Areas and Stations
The New South Wales coastline lies between latitude 28°20'S and latitude 37°20'S, with about three degrees variation in longitude from north to south (Figure
1). It is in the warm temperate (Peronian) zone (Bennett and Pope, 1953) , and is frequently broken by short, estuarine rivers, bays and coastal lakes. The bulk of the oyster community sampling was done at Wallis Lake, because of its intensive oyster fishery (Reports of the
Chief Secretary on Fisheries, 1971, 1972, 1973) and because there is a wide range of habitats in the lake. Two other areas, Sydney Harbour and Jervis Bay, were also chosen to span a latitudinal gradient. In Sydney Harbour the ex€ehsiofi''of the littoral, rock substratum a fair distance upstream makes this area most suitable for a study in the effects of salinity on oyster communities from the same substratum, , namely' sandstone rock.
2.1 Wallis Lake; is about 230 kilometers north of Sydney Harbour. It is one of the typical, coastal lakes frequently found along the New South Wales coastline. The main water body of the lake is separated by a long sand bar from the Pacific ocean, and the lake has a narrow opening between Forster and Tuncurry (Figure 2). On the north-^ west side the lake is fed by the Wollomba, McCleans and
Wallingat Rivers. Wallis Island and many other small islands are confined to the northern end of the lake, where it is considerably shallower than the southern end. The shelter and shallowness of this estuarine body of water makes it an Figure (2) Location of sampling sites at Wallis Lake ideal place for culturing oysters among the islands. Those parts of the islands which are inundated by high tide level, are well colonized by mangrove trees, with dense mats of pneumatophores on which oysters grow. The floor of the lake is mostly sandy with extensive beds of Zosteva in various places. Only the channel opening to the ocean is lined with rock and this littoral zone is crowded with oysters.
Station 1(a); Rock substratum and loose rocks at the jetty of the Fishery Office at Tuncurry. All surfaces of stones and other hard objects (wood post, iron mesh fences etc.) under high tide level are heavily colonized with oysters. The oysters are more abundant on the stones occurring in dense clumps which harbour crabs, small intertidal molluscs and worms. Close to and obtusely angled to the shore is a sand ridge which is exposed at low tide and affords considerable shelter to this oyster community.
Station ICb); is an oyster lease about two miles west of station 1(a), sited on shallow sand and
Zostera beds near the mouth of the Wollomba River. The water in this area flows very fast between tides. The site contains an abandoned oyster rack with clumps of "wild" oysters of many generations plus oyster racks of varying and known ages. The oysters of known age groups (12 months,
2 year and 3 year olds) were collected from the culturing racks.
Station 1(c) ? A further mile and a half south- west of Station 1(b) is Station 1(c), which is an oyster lease containing culture racks of one and two year old oysters suspended over a Zostera bed with its soft, muddy Figure 3 Location of sampling sites in Sydney Harbour substrate. This station is among the islands between the mouths of the Wollomba and Wallingat River. The water is rather deep and flows considerably slower than at station b.
Station 1(d); is a mangrove swamp at the south-east end of Godwin Island about two miles south of
Station 1(a) (Figure 2). That part of the island facing
Wallis Lake is about 3 feet under water at high tide. The bed of the bank is sandy and water movement is very rapid, since the island is encircled by lake drainage channels.
Oysters thrive on the bases of the mangrove trees and on their pneumatophores.
2.2 Sydney Harbour.
Two estuarine rivers, Middle Harbour and
Parramatta River, flow into Sydney Harbour (Figure 3) and run through the densely populated suburbs of Sydney, forming many bays and branches on their way. These bays are well sheltered but lack mangrove swamps. The water is deep and the shores of the Middle Harbour area are mostly lined with rock, which is colonized in the intertidal zone mainly by oysters.
Station 2 (a) ; Rocky shore just inside North
Head, near the Quarantine Station. A protrusion of North
Head extends westward forming an area which is fairly sheltered from the open sea. Although the oysters are clumped, they predominantly form a zone with individuals cemented flat on the surface. The water off shore is very deep. CURRAMBENE CREEt( 2 PACIFIC
OCEAN HUSKISSONV J E R V I S t
BAY
PT. PERPENDICULAR
BOWEN ISLAND
Figure 4
Location of sampling sites on Currambene Creek at Jervis Bay Station 2(b); Fisher Bay, east of the Spit
Bridge about three miles from the Heads, is surrounded by- houses (Figure 3). The water in the bay is shallow and sheltered, the substratum is sandy with patches of Zostera exposed at low tide and the intertidal zone is sandy with rocky headlands.
Station 2(c); Willoughby Bay is about two miles to the west of Fisher Bay in a long arm of Middle Harbour called Long Bay. This area is also densely populated with people and hilly. The water is shallow and its rate of movement is very slow. The bay has an intertidal, sandy beach, but the sand is slimy with effluent and associated algal growth, with some loose stones and rocks. The oysters are definitely unhealthy with many dead shells in the population.
2.3 Jervis Bay; is about 150 kilometers south from Sydney Harbour, The Bay is lined with sandy beaches interspersed with rocky headlands and because it is not fed by any river or large streams and has a wide mouth, the water is basically oceanic in origin. On the western side one small creek (Currambene Creek) opens into the bay at
Huskisson (Figure 4). There is no rocky shore inside the creek except at the mouth near the jetty and at the boat ramp at Huskisson. The water in the creek is shallow and the intertidal flat banks are dominated by mangroves. The creek bed is mainly sandy with many patches of Zostera,
The intertidal zone of rock, mangrove trees and pneumatophore is dominated by oysters. Station 3(a); Near the boat ramp at Huskisson, the bank of Currambene Creek is lined with stones accumulated together to prevent erosion. Here the oysters are not clumped, but are fairly well distributed over the surface of the intertidal rocks. The water offshore is rather deep.
Station 3(b); About one mile up the creek is a mangrove island associated with extensive, intertidal flats and mangroves. Between the southern bank and the island is an abandoned oyster rack over a soft, muddy
Zostera bed.
3.0 Methods
3.1 Sampling
While oyster dredges (Fleming, 1952), suction dredges (Hughes and Thomas, 1971) and SCUBA collections
(Brett, 1964) have been used successfully to collect subtidal oysters, sampling methods are restricted when tidal oysters are to be examined, for physical differences between localities and the settlement of the Sydney rock oyster on rock surfaces and on other oysters etc. make the choice of a sample unit very difficult (Wells, 1961). The sampling method adopted therefore had to be applicable to intertidal oysters which could be attached to rocks, other oysters, oyster racks, mangrove trees and their pneumatophores. Consequently quadrat sampling, or area sampling, is impractical and instead volume sampling unit was used.
For a sample to be a good sample from which valid statistical inferences may be drawn, it should be: (i) adequate (ii) unbiased and Ciii) homogeneous CSimpson et al,,
1960). When sampling communities, one of the major problems in a good sampling program is to obtain an adequate sample within the economics of time and effort. Oostring's (1956) use of the species/area curve to determine adequacy of sampling was therefore applied to this investigation, as the tediousness of examining oyster communities precludes large sample numbers with a single investigator. A plot of species against unit volume of oysters (five pints) produces a hyperbolic curve whose upper asymptote clearly indicates the number of species in the community, but only estimates the number of samples needed to fully delineate the community. As the number of samples needed to detect the rare species is disproportionate to the time and effort required, it is usual in sampling very complex communites to adopt an arbitrary level of adequacy to economically sample the community.
The arbitrary level of adequacy adopted in this investigation was that reached when a ten percent increase in sampling yielded additional species equal to ten percent of the community suite. This level of adequacy can be visually determined from the species/area curve as follows:
A line is drawn from the origin of the curve through that point on the curve representing ten percent of the species in the community and ten percent of the samples needed to fully sample the community, A second line is drawn parallel 00000000
CO y o LU Q_ CO Li. O ce UJ CD z> •Z.
25 50 75 SAMPLE SIZE (PINTS)
Figure 5
Species-Area Curve showing the minimum adequate sample size for an oyster community to the first which just touches the species/area curve. This point of contact is the adopted arbitrary level of adequacy (see Figure 5). As oyster communities in the mid-littoral zone are very homogeneous for species composition in any given locality, systematic sampling will give an unbiased, homogeneous sample for the community. Homogeneity of community structure can be tested using the variance; mean ratio for species (based on the Poisson distribution, O'Gower and Wacasey, 1967), for, if this ratio is unity or less than unity, then the community being sampled is homogeneous for species structure.
By restricting sampling to the same mid-littoral zone at all sampling sites, by systematically sampling in each selected locality and by using an adequate number of samples, the sampling procedure adopted produced good samples from which valid statistical inferences could be drawn. As the species/area curve reached its upper asymptote at 21 samples (each of five pints), and as the arbitrary 10% level of adequacy was reached at three samples (see Figure S ), the sample volume was fixed at two gallons of oysters (three samples each of five pints) for each sampling site. Samples were collected at low tide and 29 collections were made over the 19 months period of the investigation. Comparable samples were always collected during the same months (December-January) while seasonal samples were collected in February for summer. May for autumn, August for winter and November for spring and this study was done in Wallis Lake (see Locality 2 in Figure
2). For studies on the effect of oyster age on community structure, samples were collected at Locality 2 in Wallis
Lake (Figure 2), age being related to known time of spat fall.
Every sample was preserved in 8% formalin and then the individuals of all species were sorted, identified and counted. The preserved oyster flesh was oven dried to constant weight for body weigh/shell weight studies.
Shell lenghts were measured frcra the hinge to the distal edge and recorded in one of seven categories of one millimetre steps.
3.2 Analysis
A range of mathematical and statistical methods were applied to the data, each method being applied to the various appropriate problems. For example, hydrological data from the three sample localities were analysed using ANOVAR, while a series of Student "t" tests were used to compare the numbers of species between localities. Comparisons between communities, however, were based on; indices, e.g. index of diversity (Fisher et al., 1943), index of dominance (O'Gower and Wacasey,
1967), indices of similarity, such as Fager (1963),
Jaccard (1912), S^rensen (1948), Webb (1950); graphically, e.g. percentages of dry weight of tissue, tissue shell weights, regressions of Fager's index on numbers of species common to two categories; and qualitatively e.g. phylum, class groupings. The specific methods used in analysing the communities are dealt with in each appropriate section.
While indices of similarity, such as Fager (1963),
Jaccard (1912), Webb (1950) etc., have been used extensively to compare communities, arithmetic indices can give false similarities because similar algaebraic sums can be derived from widely differing components.
Again most such indices are based on three entities, namely the number of species in community "A", the number of species in community "B" and the number of species common to both communities, hence algebraic or arithmetic arrangements of these three entities will produce the same relative order of index, irrespective of the "formula" used
(O'Gower and Wacasey, 1967).
With regards indices of diversity again a range has been proposed; viz. Fisher et al., (1943) proposed
s = a log^ (1 + |) and Margalef C1951) simplified this to:
s-1 logeN while Mountford (1962) called the reciprocal (1/a) an
Index of Similarity. More recently information theory has been applied to community comparisons in the form of the
Shannon and Weaver measure of Diversity (Pielou, 1969;
Shannon and Weaver, 1949). When a range of these indices is applied to the same sets of community data, again, while the absolute values for the various indices differ markedly, depending on the "formula" used, the relative orders of similarities are the same (DeBenedictis, 1973;
Loya, 1972) . It was therefore concluded that the "best" index is the "easiest" index to calculate.
3.3 Hydrological Survey
Because of the lack of appropriate, continuous recording equipment the measurement of hydrological parameters was restricted to a study of temperature, salinity and water velocity during single, equivalent, tidal cycles at the various sampling stations at the three different localities.
Salinity and temperature were measured using a S/T meter bridge (Autolab Instruments), while the rate of flow of tidal water was measured with an almost submerged float, which was released at a given marker and its passage to a second marker timed. Salinity, temperature and water velocity were measured at hourly intervals over a full, tidal cycle, from high water through low water to high water again. Mean values for salinity and temperature were calculated while water velocities at different stations and localities were expressed graphically and means and maxima were determined.
4,0 Results and Discussions
The results of this study are presented with their discussions in appropriate sections relating to : the hydrological survey; community species compositions; species associations within the communities; and Table 1
Mean and range of salinity at various sampling sites in Wallis Lake, Sydney Harbour and Jervis Bay
Locality Station Mean (%o) Range "n"
Wallis Lake 1 32.05 6.6 12
2 30.58 9.1 12
3 30.21 6.7 11
Sydney Harbour 1 34.11 0.3 11
2 33.15 0.4 11
3 29.02 1.4 11
Jervis Bay 1 33.20 1.0 13
2 33.14 1.9 13 Table 2 ANOVAR for salinity variations at the three sampling localities
Locality Source D.F. P
Wallis Lake between stations 10,20 1.41 >0.10 over tide cycle 2,20 100.32 <0.001
Sydney Harbour between stations 10,20 247.54 <0.001 over tide cycle 2,20 3.94 <0.05
Jervis Bay between stations 12,12 0.01 >0.75 over tide cycle 2,12 11.95 <0.005 Table 3
Mean and range of temperature at various sampling stations in Wallis Lake, Sydney Harbour and Jervis Bay.
Locality Station Mean (°C) Range "n"
Wallis Lake 1 25.22 5.5 13
2 26.61 6.0 13
Sydney Harbour 1 22.47 0.2 11
2 23.24 0.6 11
3 23.44 0.5 11
Jervis Bay 1 21.36 2.7 12
2 21.51 2.4 12 associations of the communities with substrate, latitudinal location, age of community, water movement, salinity and seasonal variations.
4.1 Environmental parameters for the three localities.
The hydrological survey of the various sampling stations in the three localities: Wallis Lake, Sydney
Harbour and Jervis Bay, showed there were considerable variations in salinity, temperature and tidal flow, both between and within localities (see Table 1), ANOVAR for salinity variations at the three localities (Table 2) showed that the salinity varied significantly (P < 0.001) between stations in Sydney Harbour but not at either Wallis Lake or Jervis Bay, however, at all three localities there were significant variations in salinity over the tidal range at given stations (figures 6, 7 and 8).
Because of seasonal and weather variations temperatures at the various localities differed, but not in a very meaningful way (Table 3). However, water temperatures were always cooler and less variable nearer the sea, reflecting the more stable environment of the ocean, while there was an apparent tendency for water temperatures to inversely reflect the latitudinal gradient of the three localities. Without continuous recording instruments the data in Table 3 can only be indicative of temperature differences between sampling stations at the three localities; nevertheless, figures 9, 10 and 11 clearly indicate wide tidal temperature variations occur in both Wallis Lake and
Jervis Bay, but not in Sydney Harbour, while at all three 30
< if)
^ 5 6 7 8 TIME (HOURS)
Figure 6 Hourly variations in the salinity of the surface water, at the three stations in Wallis Lake 36,
35.
3A 1 O-
33 2 X-
32
31 —I>-
E< 30 to 29 3 •
20 ,
123A 5670 9 10 11 TIME (HOURS)
Figure 7 Hourly variations in surface salinity at the three stations in Sydney Harbour •35
33
- 32 , z H< 31 in
5 5 7 0 10 11 12 13 TIME (HOURS)
Figure 8
Hourly variation of surface salinity at the two sampling stations in Jervis Bay 23 STATIONS
22 UJ oc z> < OC Ul 0. z Ui 21
20
—r- 5 6 7 8 10 11 12 13 TIME (HOURS)
Figure 9
Hourly variation in the surface water temperature at the three stations in Wallis Lake 25
2A
23 ui a: o < -O O o- cr 1 o- .Q o o- LU a. s 22 u
123456709 10 11 TIME ^HOURS)
Figure 10 Hourly variation in surface water temperature at the three stations in Sydney Harbour 29
20
27
e 26 Oi oc u H<- ce UJ Q. 25 z Ui
2A
23
1 o
—I r —I i r -1 1 1 2 3 5 6 7 10 11 12 13 TIME (HOURS) Figure 11
Hourly variation of surface water temperature at the two sampling stations in Jervis Bay 5 6 7 TIME (HOURS)
Figure 12
Hourly variation in the rates of low of tides at the three stations in Wallis Lake UJ I— 3 Z z
LU U. 5 o
- 2345S789 TIME (HOURS) Figure 13 Hourly variation in rates of tidal flow at the three stations in Sydney Harbour 70 J 60 LU 3 z 50j H LU LU UL 40 o _J Z 30 j u. o UJ < QC 20 I 1 o lOj -TT r 10 12 13 TIME (HOURS) Figure 14 Hourly variations in rates of tidal flow at the two stations in Jervis Bay Table 4 Mean and maximum water velocities at various sampling stations in Wallis Lake, Sydney Harbour and Jervis Bay Locality Station Mean(ft/min) Maximum "n" Wallis Lake 1 14.62 22.6 12 2 43.47 100.0 12 3 18.47 38.7 11 Sydney Harbour 1 24.57 40.0 11 2 24.71 60.0 11 3 3.63 8.3 11 Jervis Bay 1 19.41 34.2 13 2 45.81 100.0 13 localities there was a tendency for sampling station temperatures to maintain estuarine gradients from upstream to mouth over the tidal cycles. As to be expected tidal velocities varied both between and within localities (Table 4), but with a tendency for bimodal velocities related to the tidal cycles (figures 12, 13 and 14), Maximal velocities occurred at Station 2 in all three localities. In terms of water velocity Stations 2 and 3 in Wallis Lake are comparable to Stations 1 and 2 in Sydney- Harbour v^ich occupy an intermediate position between those of Wallis Lake and Jervis Bay. 4.2 Species composition of oyster communities. The 83 species found in the 21 communities collected at the eight sampling stations in Wallis Lake, Sydney Harbour and Jervis Bay (figures 2, 3 and 4) are shown in Appendix I, and include 33 molluscs, 12 annelids, 4 nemerteans, 1 sipunculid, 3 flat worms, 1 phoronid, 23 arthropods, 1 coelenterate, 1 echinoderm and 4 fish. Protozoans, copepods, ostracods and nematodes were not identified or examined in detail. The 83 species occurred in areas which differed in environmental conditions such as substrate, age of oysters, water movement and latitudinal location, salinity and season. Although sampling was restricted by the economics of time, effort and the cost of oysters, it is assumed in classifying these communities that all species had the same probability of being present in all communities and hence any absences of various species were related to differences in the coimnunities and not to any deficiencies in sampling. While Fleming (1952) has reported 101 species of animals associated with Ostrea sinuata in Australian waters there are no detailed studies on animal communities associated with the southern commercial oyster Saocostrea ouooullata oommevcialis, In the North Sea, Mobius (1977) described 24 species of animals associated with Ostrea edulis but Gaspers (1950) later listed 208 species in North Sea oyster beds. In England, Mistakidis (1951) listed 92 and 116 species of animals collected in two different beds of 0. edulis, while Korringa (1951) found 136 species associated with the shells of 0. edulis, but this list included 27 copepods, 6 ostracods and 17 nematodes, groups not covered in the present study. In Puerto Rico, Mattox (1949) found 39 species of animals associated with Crassostrea rhizophorae, while in the United States, Pearse and Wharton (193 8) found 139 species of animals associated with Crassostrea virginica in Apalachicola Bay and Frey (1946) reported 53 species in beds of this oyster in the Potomac River, In Beaufort Harbour, North Carolina, MacDonald (1940) listed 68 species of animals in C. virginica beds, but Stephenson and Stephenson (1952) found 105 species of plants and animals associated with these oysters, while Well (1961) found 303 species of animals in C, virginica beds in the same locality Recently, Hughes and Thomas (1971) reported 62 species of animals in C. virginica beds in Bedeque Bay. It is difficult to reconsile this large variation in species diversity for C. virginioa beds, unless beds of varying ages were sampled, or unless seasonal variations associated with the survival of transport, semi-typical species, could account for these variations in diversity. There are no published surveys of organisms associated with the Australian oyster Saooostrea cucoullata commeroialis. However, it is clear that oyster beds can support a large fauna, but the faunal composition of beds varies with environmental conditions. The 83 species present in this study were collected at Wallis Lake, Sydney Harbour and Jervis Bay, areas which differed in environmental conditions, such as substrate, age of oyster, water movement, latitudinal locality, salinity and time (season). Thus for homogeneity and validity in classifying and comparing communities it is assumed that every species found in the communities has the same chance of being present in all communities, as every habitat is basically similar, i.e. oyster shells. 4.3 Similarities between communities. An important aim of this ecological survey is to classify the different communities in terms of similarities. Various methods have been employed in the past to attain this aim, the simplest of these being the calculations of indices of similarity such as Jaccard's (1912). His definition of Coefficient of Similarity was: S = J/(a + b j) , where a is the number of species in community A b is the number of species in coiranunity B, and c is the number of species common to both communities. While such indices (Jaccard, Sorensen, Fager and Webb) vary with sample size and with algaebraic composition, they can indicate similarities between communities using the appropriate safeguards. Mountford'^s (1962) Index of Similarity: al , bl (a + b - j)I, where e is the e + e = e ' base of natural logs, depends upon the logarithmic relationship between the number of species and the number of individuals in a series of random samples from a given community, as suggested by Fisher et al* (1943). Consequently, Mountford's Index is to be preferred to the other indices, especially as this index is independent of sample size, for this log function is a hyperbola which can be transformed into a linear regression. However, sampling should be discontinued at the upper asymptote and such a procedure would eliminate the major drawback of the arithmetic indices of Sorensen (1948), Jaccard (1912) and others. As the sample number for this study was derived from the ten per cent rule (Oostring, 1956), sample number will not affect the arithmetic indices. Mountford (1962) also developed a method for similarity grouping of communities to form a hierarchial dendrogram. The indices of similarities for various communities are grouped viz. I (Al A2 —— Am; Bi B2 Bn) = i [jAiB + I(AmBi) + I (AmBn)^ The classification is derived by combining the Table 5 Mouiitford indices of similarity between oyster communities in the sampling localities MONTH HABITAT LOCALITY KEY A B C D E F G H I J K L M N P Q R S T U V May Oyster rack (J.B) A .195 .143 .084 .024 .061 .064 .026 .051 .027 .094 .075 .083 .083 .066 .166 .067 .083 .108 .031 .030 May Pneumat- (J.B) B .262 .091 .040 .099 .084 .042 .072 .036 .217 .080 .101 .101 .093 .400 .109 .135 .178 .042 .047 ophore May Mangrove (J.B) C .071 .033 .076 .066 .034 .072 .036 .154 .059 .077 .077 .073 .400 .083 .101 .178 .034 .037 May Oyster rack (W.L) D .041 .066 .105 .024 .046 .046 .080 .105 .115 .151 .072 .089 .286 .057 -091 .054 .055 Aug. Rock (J.B) E .063 .069 .028 .041 .039 .043 .020 .032 .038 .021 .047 .051 .032 .060 .034 -061 Aug- Rock (W.L) F .151 .051 .073 .037 .087 .039 .098 .098 .036 .136 .100 .098 .176 .087 .098 Aug. Oyster rack (W.L) G .031 .072 .042 .121 .058 .083 .105 .066 .116 .175 .105 .195 .069 .060 Aug. North Head (S.H) H .056 .035 .038 .020 .028 .034 .017 .059 .024 .049 .052 .061 .076 rock Aug. Wi1loughby (S.H) I .083 .098 .033 .069 .107 .044 .111 .046 .137 .112 .056 .063 rock Aug. Fisher B (S.H) J .039 .028 .035 .050 .023 .039 .048 .042 .055 .035 .061 rock Nov. Oyster rack (W.L) K .096 .222 .118 .132 .205 .124 .118 .113 .041 .034 Dec. 2-yr (Fast) (W.L) L .159 .066 .084 .080 .126 .066 .043 .031 .026 Dec. 3-yr (Fast) (W.L) M .190 .089 .087 .109 .080 .077 .049' .038 Dec. 1-yr (Slow) (W.L) N .089 .124 .109 .137 .135 .060 .056 Dec. 2-yr (Slow) (W.L) P .101 .088 .071 .073 .031 .023 Dec. 1-yr (Fast) (W.L) Q .104 .286 .400 .059 .059 Feb."" Oyster rack (W.L) R .085 .109 .057 -055 May Mangrove (W.L) S .186 .059 .046 May Pneumat- (W.L) T .054 .091 ophore May Rock (W.L) U .056 May Rock (J.B) V pair of communities having the highest indices of similarity to form a single group. The index for this group is then combined with the indices for all other communities to produce the next highest index. The procedure is repeated until the table is reduced to a single value with the combination of all communities. Table 5 shows the initial trellis diagram of the 21 communities using Mountford's method (see Table 5), while the resultant hierarchial grouping of all the communities is given in figure 15. Mean densities and variances for numbers of species and individuals, indices of diversity and dominants, number of species and variance mean ratio for species are given in Table 6. Margalef's (1951) modification of the Fisher et at* (1943) index of diversity a has been calculated, where a = (s - D/log^N, where s = number of species and N = number of individuals and this index, together with the O'Gower and Wacasey (1968) index of dominants and mean densities of both species can also be used to compare communities. As these techniques are independent of taxonomic categories, their value is particularly suited to comparing communities, either from geographically seperated localities, or from different habitats. Consequently these techniques supplement the hierarchial presentation of similarity indices of Mountford (1962). From the trellis of Mountford indices (Table 5) 4F 58 50 76 83 91 81 ,104 115 Tie 139" 154 151 222 m SAMKN FGDRL PI J HVUE B C T Figure 15. Hierarchial dendrogram for community associations in the Wallis Lake, Sydney Harbour and Jervis Bay oyster communities KEY A Oyster rack, Jervis Bay, May L Two-year-fast, Wallis Lake, December B Pneumatophore, Jervis Bay, May M Three-year-fast, Wallis Lake, December C Mangrove, Jervis Bay, May N One-year-slow, Wallis Lake, December D Oyster rack, Wallis Lake, May P Two-year-slow, Wallis Lake, December E Rock, Jervis Bay, August Q One-year-fast, Wallis Lake, December F Rock, Wallis Lake, August R Oyster rack, Wallis Lake, February G Oyster rack, Wallis Lake, August 1 S Mangrove, Wallis Lake, May H Noth Head rock, Sydney Harbour, August T Pneumatophore, Wallis Lake, May I Willoughby rock, Sydney Harbour, August U Rock, Wallis Lake, May, J Fisher Bay rock, Sydney Harbour, August V Rock, Jervis Bay, May K Oyster rack, Wallis Lake, November Table 6 Number of species, mean numbers and variances of species, and indices of diversity and of dominants for oyster communities on rock surfaces, racks and mangrove pneumato- phores in Wallis Lake and Jervis Bay. Statistic Index Locality Habitat No. sp. X sp. s^ sp. a I.D. Wallis L. rock 30 15.4 7.76 3.52 0.006 rack 23 11.9 2.64 3.00 0.016 pneum. 24 9.6 1.92 3.32 0.024 Jervis B. rock 28 17.0 0.50 3.11 0.002 rack 15 10.2 2.29 1.78 0.009 pneum. 18 9.9 4.07 2.25 0.013 Table 7 Selected indices of similarity, based on occurrences, between oyster communities on rocks, oyster racks and mangrove pheum- atophores in Wallis Lake and Jervis Bay COMMUNITIES a b c Fager Jaccard Sorenson Webb O.R {J.B)/Pn (J.B) 15 18 14 0. 9783 0. 7368 0. 8484 0. 2978 Pn (W.L)/Pn (J.B) 24 18 16 0. 8726 0. 6153 0. 7619 0. 2758 Rock (W.L)/Rock (J.B) 30 28 22 0. 8382 0. 6111 0. 7586 0. 2750 O.R (W.L)/O.R (J.B) 23 15 13 0. 8036 0. 5200 0. 6842 0. 2549 Pn (W.L)/O.R (J.B) 24 15 13 0. 7866 0. 5000 0. 6666 0. 2500 O.R (W.L)/Pn (W.L) 23 24 16 0. 7602 0. 5161 0. 6808 0. 2539 O.R (W.L)/Rock (J.B) 23 28 17 0. 7478 0. 5000 •0.666 6 0. 2500 O.R (W.L)/Pn (J.B) 23 18 13 0. 7242 0. 4642 0. 6341 0. 2407 Rock (W.D/O.R (W.L) 30 23 16 0. 6800 0. 4324 0. 6037 0. 2318 Rock (W.L)/Pn (W.L) 30 24 16 0. 6640 0* 4210 0. 5925 0. 2285 Pn (W.L)/Rock (J.B) 24 28 15 0. 6444 0. 4054 0. 5769 0. 2238 Rock (J.B)/O.R (J.B) 28 15 12 0. 6723 0. 3870 0. 5581 0. 2181 Rock (J.B)/Pn (J.B) 28 18 12 0. 6059 0. 3529 0. 5217 0. 2068 Rock (W.L)/Pn (J.B) 30 18 12 0. 5853 0. 3333 0. 5000 0. 2000 Rock (W.D/O.R (J.B) 30 15 10 0. 5413 0. 2857 0. 4444 0. 1818 Key: O.R. = oyster rack Pn = pneumatophore W.L. = Wallis Lake J.B. = Jervis Bay a = number of species in b = number of species in c = number of species in and the associated hierarchial dendrogram (Figure 15) the greatest similarities existed between communities from: one-year-old oyster racks in fast flowing water in Wallis Lake, mangrove trunks in Jervis Bay and mangrove pneumatophores in Wallis Lake (I is approximately 0.4 in Table 5), while I values approaching 0.3 indicate that the oyster racks in Wallis Lake, one-year-old and three-year- old oysters in fast flowing water in Wallis Lake mangroves and their pneumatophores in Jervis Bay and the Jervis Bay pneumatophores with the oyster racks in Wallis Lake support fairly similar communities. On the other hand 16 of the 20 highest similarities in the trellis involved oyster rack communities, indicating that such rack communities were very similar irrespective of variations in the age of the rack, the rate of flow of water or seasons. Using Fager, Jaccard, Sorensen and Webb indices of similarity, based on occurrences and joint occurrences, Table 7 clearly shows that the oyster racks and pneumatophores of Jervis Bay are most similar with pneumatophores of Wallis Lake and Jervis Bay next and rock surface of Wallis Lake and Jervis Bay next. Using mean densities, indices of diversity and dominants Table 6 shows that: the rock surfaces of Wallis Lake and of Jervis Bay support similar oyster communities, the oyster racks in Wallis Lake support communities similar to those on the pneumatophores in Wallis Lake and similarly the oyster racks and pneumatophores of Jervis Bay support similar communities. However, on the basis of mean densities rock surfaces support the highest Table 8 Numbers of species (n > 10%), by Phylum and Class, in oyster communities on rock surfaces, oyster racks and pnexamatophores in Wallis Lake and Jervis Bay Wallis Lake Jervis Bay Phylum and Class Rock Rack Pneum. Rock Rack Pnevim. Annelida Polychaeta 4 4 3 4 2 2 Arthropoda Crustacea 6 7 7 o 6 7 Mollusca Amphineura 2 0 0 2 0 0 Gastropoda 11 4 6 10 2 4 Lamellibranchia 3 3 4 3 3 2 Sipunculida 1 0 0 0 0 0 Phoronida 1 1 1 1 1 1 Nemertean 0 2 0 0 0 0 Platyhelminthes Trematoda 1 1 1 1 1 1 Colenterata Actinozoa 1 1 1 1 0 0 Chordata 0 0 1 0 0 1 Pisces densities, then oyster racks and then the pneumatophores for both localities. In terms of both diversity and of density rock surface oyster communities are very similar, while oyster rack and pneumatophore communities in the same localities are more similar than similar habitats in different localities. When one examines the numbers of species from various phyla and classes in the oyster communities (Table 8) it is again apparent that rock surface communities are very similar, while the rack and pneumatophore communities in the same locality are more similar than similar communities in different localities. From the above it would appear that if one considers seasonal and habitat variations the similarities are greatest between May samples of the oyster communities on the mangroves and their pneumatophores in Jervis Bay and the December samples from oner-yearr-old oyster racks in Wallis Lake, which in turn are similar to the May samples from oyster communities on the mangroves and their pneumatophores in Wallis Lake, Omitting seasonal variations, the oyster communities on rock surfaces from different localities are very similar, whereas oyster communities on oyster racks and on mangrove pneumatophores are more similar in the same locality than those on similar habitats (oyster racks or mangrove pneumatophores) from different localities. However, there is some degree of similarity between the oyster communities on the pneumatophores in both Wallis Lake and Jervis Bay. Finally all oyster rack communities show a high degree of similarity. While it might be expected that animal communities associated with a sessile, littoral animal, such as the oyster, could show variations in both density and diversity related to zonation, as occurs on the ocean rock platforms (Dakin, 1952; Guiler, 1950, 1960; Newton and Cribb, 1951), nevertheless both naturally occurring and cultivated oysters seem to be restricted to the lower to mid littoral zone and hence are not exposed to tidal extremes of desiccation, insolation and temperature. As cultivated oysters are virtually "planted" at the "best" level within the intertidal zone^ it is to be expected that the communities supported by oyster racks should show a greater degree of similarity and a lower diversity than communities in naturally occurring oysters. While this is true in part, the oyster communities associated with rock surfaces were not only very diverse because of the larger tidal flux associated with the location of the sampling sites (nearer the ocean than the other habitats), but they were also very similar. This similarity is due, of course, to the similarity in the environment bathing these sampling sites. In the gross analysis of communities the effects of environmental factors of latitude, age of oyster and water movement on community similarities and differences were not marked. It must be borne in mind that each community is influenced by many ecological factors simultaneously and hence only dominant factors will make their effects apparent. Further examination of these communities in relation to single, environmental factors may, however, further elucidate this problem. 4.4 Associations between species. An examination of the species composition of communities associated with oysters may help elucidate some of the relationships between the animals in the communities and so help explain the ecology of such communities. There are various ways of describing the biological composition of communities and one such method is to study the associations between animals in a quantitative manner; however, it may also be desirable to examine the composition of communities in terms of their component species. The quantitative description of the species composition of a community can be made using coefficients of association, originally proposed by Pearson (1904) and used by Debauche C19 62), Davis (19 63), O'Gower and Meyer (1963) and others in various studies. The coefficient of association between two species is based on the assumption that both species have equal chances of occurring in all samples and the degree of association is measured by the observed joint occurrences of both species relative to that expected by chance. The coefficient of association is defined by: ^ - and the N + x' significance of such association is given by: 2 ^ N [(ad - be) - ^ (a+c) (b+d) (c+d) (a+b) 1 d.f. where^ cn Table 9 Coefficients of association between the 22 most cominon species in the oyster communities of Wallis Lake and Jervis Bay A B C D E F G H I J K L M N P Q R S T U V Bembiaiim auratum A .21 .21 .29 .43 .01 .08 .46 .46 .05 .04 .46 .04 .05 .17 .04 .01 .05 .01 .05 .01 Mytilus edulis B .03 .10 .22 .02 -14 .29 .29 .10 .21 .29 .31 .18 .02 .06 .02 .18 .24 .18 .02 Notirus arenatus C .09 .22 .02 .14 .29 .29 .35 .21 .29 .06 .18 .02 .21 .02 .10 .02 .10 .02 Lasaea austvalis D .29 .14 .06 .34 .34 .08 .11 .34 .11 .08 .42 .11 .17 .08 .17 .24 .14 Chezaemaaa flamea E .01 .08 .46 .46 .05 .04 .46 .04 .05 .17 .04 .01 .05 .01 .05 .01 Austvoaodhtea obtusa F .03 .21 .21 .41 .23 .21 .04 .31 .09 .04 .53 -13 .23 .06 .58 Littovina aautiopira G .22 .22 .03 .10 .22 .29 .35 .04 .10 .03 .17 .03 .03 .23 Fevinereis cmblyodonta H .45 .22 .21 .45 .21 .22 .27 .21 .21 .22 .21 .22 .21 Booavdia sp. I .22 .21 .45 .21 .22 .27 .21 .21 .22 .21 .22 .21 Syllis sp. J .50 .22 .02 .29 .01 .18 .31 .11 .06 .11 .25 Flatworm (1) K .21 .25 .20 .05 .12 .15 .20 .04 .38 .23 Ehninius modes tus L .21 .22 .27 .21 .21 .22 .21 .22 .21 B. amphitvite M .01 .05 .25 .15 .35 .32 .18 .04 T. purpuras cens N .01 .20 .25 .32 .06 .09 .31 S. eugthrodaotyla P .28 .14 .01 .10 .01 .32 P. monilifer Q .04 .38 .04 .20 .23 E. spinosus R .06 .14 .13 .39 S. quoyana S .13 .28 .31 Metita T .13 .05 Talitroidea U .06 Sea anemones V a is the number of samples containing both species, b and c are the numbers of samples containing either species, d is the number of samples containing neither species and N is the number of samples. Using recurrent groups Fager (1957) proposed a method for grouping associations, but the method is flexible. Whittaker and Fairbanks (1958) and Davis (1963) plotted associations diagrammatically but two dimensional diagrams cannot fully describe such associations. Hughes and Thomas (1971) expressed their associations in a dendrogram using a method similar to that used by Mountford (1962). The hierarchial dendrogram does reveal community structure in a clear manner while the magnitudes of association are accurately presented. Coefficients of association were calculated for all pairs of the 22 most common species in the oyster community, with x^ ^3,84 at the 5% level of significance. The results of these calculations are presented in Table 9 as a trellis diagram, with signs of associations (+ or -) and levels of significance (88 indicates 1% level and * indicates 5% level). Figure IS presents a hierarchial dendrogram of these associations calculated using Mountford's (1962) method. Of the 210 terms in the trellis diagram 128 were positive, 82 were negative, but only 16 were significant. Of these sixteen associations, Boooardia sp., Perinereis amhylodonta and Elminius modestus occurred in all communities, 11 associations were positive, and two associations were negative. Significant positive associations can be interpreted in a variety of ways; the two species may utilize the same food resource^ share the same habitat or be directly linked in a predator-prey relationship. As not enough is known of the biology of most species in oyster communities it is not possible to say which factor caused the association, nevertheless these results may indicate possible lines for future investigation. The hierarchial dendrogram of the 21 species classifies the animals into three groupings. Group I consisted of animals which were most common in the communities and of course included the three, ubiquitous species Boaoardia sp,^ P. amblyodonta and E, modestus, Both the annelids Boaoardia sp. and P. amblyodonta are carnivores and scavengers which live in the debris associated with oyster shells. E, modestus is the most common intertidal barnacle in N.S.W, estuaries with a wide tolerance for suspended detritus mud etc., and able to utilize virtually any substrate for attachment and growth (Pope, 1945). While some carnivorous annelids feed directly on barnacles (Moore, 1958) very few empty shells of E, modestus were noted indicating that these barnacles did not form the bulk of the food of these predatory annelids. It would therefore seem likely that the constant occurrence of these two worms with E, modestus was fortuitous and was not a predatorr-prey relationship. The two, herbivorous gastropods, Bemhicium auratum ' and Chezaemaea flamaea were associated with each other (x^ = 4.73) and with the three constant species (X^ = 5.51). Strangely these two animals were absent from site 3 in Wallis Lake, otherv7ise these two species would also have been ubiqutous throughout the oyster communities. These five species form the dominant group of animals in oyster communities. Another significant association in the Group I animals is between the common mangrove crab Sesavma erythvodactyla and the small bivalve Lasaea australis (X^ = 4.49). As L, australis occurs in sheltered positions between the oysters shells^ as S, erythrodactyla commonly shelters in the crevises of oyster shells in the mangroves and elsewhere, and as both of these species do not occur in localities with high rates of water flow, it would seem that the shelter from water currents afforded by oyster shells could be the major reason for the close association of these two species. Finally the isopod Sphaeroma quoyana and the amphipod Talitroides sp, form the last pair of animals in Group I, but the association between these two species was not significant Cx^ = 0.28), As both species are detritic feeders or scavengers it seems likely that oysters form a convenient habitat for these small crustaceans. The Group II animals included one mollusc Mytilus edutis and" three arthropods Balanus amphitrites, Eviooheir spinosus and Melita sp, but the associations between these three species were not significant. There seemed to be little in common with these three species. The Group III animals consisted of three molluscs, Austrocochlea obtusa^ Littorina acutiospira and Notirus crenatus, one annelid Syllis sp,, one anemone, one polyclad and two crustaceans, Pilumnus monilifer^ Most of the animals in this group occurred on rock surfaces and there were two significant associations between pairs of species. The gastropod A, ohtusa was associated with sea anemonies (x^ = 10,97) while the two worms were also associated together (x^ = 7^07), As A, ohtusa dominantly occupies the rock pool subhabitat (O'Gower and Meyer, 1971) on rock platforms, as do sea anemonies^ it is to be expected that these two species could find suitable habitats amongst oyster shells on the rock surface. Similarly the two worms would also share the same habitat requirements of shelter from desiccation and could presumably both have similar feeding requirements or alternatively they could form a predator-prey relationship. The association of T. purpurasaens and L. aoutispria would also seem to have similar habitat requirements, probably associated together by their need for fresh, tidal ocean water. As T,^ purpurasaens also is limited to shaded habitats, CPope, 1945), may be the shade afforded by oyster shells attracts both of these species. The remaining pair in the group N^ erenatus and P, monilifer were only weakly attached to the group. Both of these crabs no doubt find the more saline ocean water of the preferred rock habitat more suited to their physiological osmoregulatory capabilities while finding the oyster shells also provide suitable shelter from adverse desiccation and probably also shelter from predation. Of the associations in the 21 species matrix most are almost certainly due to similar microhabitat requirements which give shelter from desiccation, insolation, water movement and predation. It is also probable that the rock-oyster type habitat supplies algae suited to a range of herbivores such as the rasping gastropods. It is doubtful whether many direct predator/prey relationships occurred within these groups of animals. It is therefore concluded that most groupings of animals were related to similarities in requirements for shelter from predators Cfish?), desiccation, insolation, osmotic stress and other environmental parameters, rather than to direct predator/ prey relationships. 4.5 Substrate and latitudinal effects on oyster communities. To study the effects of substrate and latitude on the species structure of oyster communities samples (12, two-point samples) were collected at the same time from rocks, oyster racks and mangrove pneumatophores at adjoining localities in Wallis Lake and in Jervis Bay,, about 300 miles apart. The sampling sites were as similar as possible for environmental parameters, and substrate and latitudinal effects on oyster communities were assessed using community indices, similarity indices and statistical tests e.g. "t" test, ANOVAR, S^ ; X, plus body weight-shell weight comparisons and matrix of contingency coefficients for community species. The community and similarity indices calculated for this study were: 1. Species richness = number of species in the community 2. Index of diversity (a) = s-l/log^N, where s = number of species, N = number of individuals in the community CFisher et alii, 1943; Williams, 1947). 3. Index of dominants = number of species forming the median number of individuals divided by the mean number of individuals per sampling unit. 4. Mean and variance, normal statistical terms, 5. Variance to mean ratio in which randomness = 1 ± 2 /2n/(n-l)^, giving a value of 1 ± 0.991 when n = 12. 6. Fager index of similarity = c/C/ab — ^/b, where b > a CFager, 1963) . 7. Jaccard index of similarity = c/(a + b ^^ c) CJaccard, 1912) 8. S0rensen index of similarity = 2c/(a + b) (S^rensen, 1948). B Size Categories ^ ^ too, 6 90 \ 80 . \ 70 60- \ %Q AO 30 . 20 10 0 J.B S.H W.L J.B S.H W.L Figure 16. Percentage number (A) and percentage dry weight (B) (tissue and shell) of seven, size categories of oysters from rock substrates at Jervis Bay (J.B.), Sydney Harbour (S.H.) and Wallis Lake (W.L.). 9. Webb index of similarity = c/Ca + b + c) (Webb, 1950), where a ^ number of species in community A, b " number of species in community B and c number of species common to both communities. The weights of tissue and shell of oysters in seven, size categories from the three substrates at the two, selected localities were determined and the data presented as graphs. The percentages of numbers and weights of the seven size categories of oysters were presented in cumulative block diagrams. As oysters comprise the substrate for the animal communities assocated with oysters an examination was made of the oysters from Wallis Lake and Jervis Bay (Chapman, 1949; Moore and Kitching, 1939; Wilson, 1937), in spite of Well's (1961) claim that the type of substrate should be ignored, for it is apparent that crevices are important habitats and crevices must vary with different size oysters. As rock surfaces are a natural substrate for the Sydney rock oyster and span a wide tidal range, as oyster racks are restricted to a fixed tidal level, as mangrove pneumatophores are restricted to a narrow tidal range and as the rock substrate had the highest species richness (number of species, see Table 6), the oysters of the rock communities at both Wallis Lake and Jervis Bay were compared for differences in "shell substrate^'. From figure 16 it appears that in terms of both density and dry body weight the rock oyster communities of Jervis Bay, Sydney Harbour and Wallis Lake were composed mainly of medium sized individuals, but there was a tendency for the Jervis Bay oysters to be dominated by category three .100. o SIZE CATEGORY 1 2 .090 . 3 A 5 .080 6 < q: .070 . Xo LmU .060 •050 J LU X C/) ZLU) CO CO .030 J .02 0 MEAN : .0^3 .036 .01 0 . 0 J.B S.H W.L Figure 17. Tissue : shell dry weight ratios of seven, size categories of oysters from rock substrate at Jervis Bay (J.B.)/ Sydney Harbour (S.H.) and Wallis Lake (W.L.). oysters in both density and weighty whereas the Wallis Lake oysters were dominated by categories one and two in density with nearly all size categories about equal in weight. From figure 17 the relationship between latitude and tissue to shell weight ratios is a regression, being greatest at Jervis Bay and least at Wallis Lake, Applying ANOVAR to tissue/ weight ratios of oyster substrates at Wallis Lake and Jervis Bay and of rock substrate at the two localities gave the following: F d.f. P BETWEEN ROCK, RACK, PNEUMAT. W.L. 0.0130 4, 10 >0.75 BETWEEN ROCK, RACK, PNEUMAT. J.B. 0.2056 5, 12 >0.75 BETWEEN ROCK, W.L., SYD.H., & J.B. 6.0100 5, 12 <0.01 Clearly latitude affects the tissue weight ratio of oysters forming the substrate for oyster communities. This trend is probably associated with the effects of increased temperatures with latitude (Table 3) on the rate of shell deposition (Moore, 1955), rather than due to a decrease in tissue growth (Dane, 1972; Dehnel, 1955), or to crowding effects (Isham et al,, 1951; Moore, 1935). From these data it would seem that a study of the effects of latitude on growth rates and tissue to shell weight ratios of oysters would be most rewarding. An examination of "shell substrate" at both Wallis Lake and Jervis Bay shows that both areas provide somewhat similar habitats for oyster communities, with a tendency for the Wallis Lake oysters to be more uniform in size and with the Jervis Bay oysters tending to be somewhat dominated by smaller oysters. Such a difference would affect the availability of crevices and hence affect the densities of "crevice-living" animals for larger oysters produce larger crevices and smaller oysters form a more even exterior surface to the environment. If these oyster communities be now examined, first in mathematical and statistical terms and second in biological terms, what effects will substrate and latitude have on oyster communities? If an environment is heterogeneous for those parameters which affect species composition of communities then a series of random samples should yield variable numbers of species in each sample, i.e. a large variance. On the other hand if the environment is homogenous then such a series of samples should yield uniform numbers of species in the samples. Homogeneity of environment may most easily be determined from the variance to mean ratio for ninnbers of species in a series of random samples, based on the Poisson distribution (see O'Gower and Wacasey, 1967). All the variance to mean ratios for all sampled communities were low (Table 6) indicating that the oyster habitat was uniform for numbers of species for all communities studied. Consequently statistical analysis of the field data should yield valid conclusions. Using ANOVAR on the numbers of species in the oyster communities the analysis gives: F d.f. P BETWEEN SPECIES 8.6153 1, 4 <0.05 BETWEEN LATITUDES 0.5500 2, 3 0.50 which indicates there was a significant difference in the numbers of species of oyster communities from various substrates. Table 10 "t" values and probabilities for differences in the numbers of species in oyster conununities from rocks, oyster racks and mangrove pneumatophores in Wallis Lake and Jervis Bay. Community Rock (W.L.) V Rock (J.B.) 1.9286 0.10 Rack (W.L.) V Rack (J.B.) 2.6525 <0.02 Pneum. (W.L.) V Pneum. (J.B.) 0.4246 0.50 Rock (W.L.) V Rack (W.L.) 3.7598 <0.01 Rock (W.L.) V Pneum. (W.L.) 6.2305 <0.001 Rack (W.L.) V Pneum. (W.L.) 3.7313 <0.01 Rock (J.B.) V Rack (J.B.) 14.1020 <0.001 Rock (J.B.) V Pneum. (J.B.) 11.5035 <0.001 Rack (J.B.) V Pneum. (J.B.) 0.4120 0.10 but not from different localities (see Table 6 for mean densities) However, Students "t" test between localities and between substrates (Table 10) showed there was a significant difference between the numbers of species in oyster racks from Wallis Lake and from Jervis Bay (latitude), but not between the numbers of species on oyster racks and on pneumatophores at Jervis Bay (substrate). Notwithstanding these two exceptions the overall pattern of "t" values closely follows the ANOVAR analyses. Table 6 shows how these values differed, thus species richness (number of species) was greatest on rock surfaces, next on pneumatophores and least on oyster racks for both Wallis Lake and Jervis Bay, but species richness was greatest for each substrate at Wallis Lake than at Jervis Bay. As the index of diversity (a) also followed this pattern it is apparent that the above analyses were meaningful. In terms of dominance (Index of dominance. Table 6) rock oyster communities were dominated by smallest numbers of species, oyster rack communities were dominated by more species, while pneumatophore communities were dominated by the largest number of species. Applying the index of dominance to latitudinal differences in oyster communities the Jervis Bay communities was dominated by fewer species than the corresponding Wallis Lake communities. Apart from statistical and community index analysis the oyster communities of Wallis Lake and Jervis Bay can be examined in terms of similarity. Based on occurrences of species communities may be compared using indices of similarity (Fager, 1963; Jaccard, 1912; SjzJrensen, 1948; Webb, 1950), some of which are arithmetic (Jaccard, Sorensen and Webb), others are geometric (Fager), but O'Gower and Wacasey (1967) pointed out Table 11 Exclusive species occurring in rock, rack and pneumatophore communities at Wallis Lake and Jervis Bay. Substrate Locality Rock Rack Pneumatophore Wallis Lake Aoanthoohitona sp. Af. edulis B. nanum E* epinosue L. gaimavdi Melita sp. M. aonoidea Nemertean M. marginalba S. dentioulata B. hanleyi P. monilifera t Jervis Bay Aoanthoohitona sp. flatworm Orphicavdellus sp. S. septentriones P. monilifev A. obtusa Talitvoidea sp. B. nanum L. aoutispria M. aonoidea N. melanotvagus S. dentioulata Sea anemone C. antennatus T. purpurasoena Syllis sp. 0. patelloides Table 12 "F" values and probablilites for comparisons between the densities of the nine species common to the three substrate communities at Wallis Lake and Jervis Bay. Species Environment D.F1 "F" values P B. aura turn Between substratum 1, 4 0.9468 0. 25 Between latitudes 2, 3 0.0069 0. 75 c. flammea Between substratm Ir 4 7.1963 0. 05 Between latitudes 2, 3 0.0173 0. 75 L. austvalis Between substratura 1, 4 23.1757 0. 01 Between latitudes 2, 3 0.1245 0. 75 N. ovenatua Between substratum 4 2.5104 0. 10 Between latitudes 2, 3 1.3469 0. 25 P. amblyodonta Between substratum 1, 4 6.7738 0. 05 Between latitudes 2, 3 0.0203 0. 75 Boaoardia sp. Between si:ibstrati3m 1, 4 1.0461 0. 25 Between latitudes 2, 3 4.2682 0. 10 5. erythrodaotyla Between substratum 1, 4 7.2777 0. 05 Between latitudes 2, 3 0.0352 0. 75 E, modestus Between substratum 4 2.9108 0. 10 Between latitudes 2, 3 0.2784 0. 75 G. aaespitoea Between substratum 1, 4 18.5946 0. 025 Between latitudes 2, 3 0.0934 0. 75 that arithmetic indices suffered from more disadvantages than did geometric indices, but all indices gave the same "order of similarity". Table 7 illustrates this latter point. From Table 7 it appears that the oyster rack and pneumatophore communities at Jervis Bay were the most similar communities. As these communities were adjoining this result is not unexpected, however, apart from this example the greatest similarities existed between the same types of substrate communities from different latitudes, while the least similarity existed between communities from rock substrate and the other substrates. Similarity indices therefore reflect the same differences and likenesses as did the statistical and mathematical analyses; namely, substrates differ more than does latitude in terms of oyster community structure. Using biological criteria of species composition both the Wallis Lake and Jervis Bay, rock oyster communities contained more "exclusive" species than did the communities on other substrates. However, in Wallis Lake the oyster rack community contained more "exclusive" species than did the pneumatophore community, whereas at Jervis Bay the reverse held (Table 11). Other than this the restriction of the Amphineura to rock substrate and of Pisces to pneumatophores, albeit at very low densities were to be expected and the numbers of species by Phylum and Class were very similar (Table 8) and added little to our understanding. Finally, while it might be trite to compare indicator species from the three substrates at the two localities, because indicator species are of doubtful value in latitudinal comparisons, nevertheless of the 47 species found in the oyster communities (Appendix 1), nine species occurred in all communities, but only two showed any significant associations (ANOVAR) with substrate (Table 12), viz. Lasaea australis and Galeolaria caespitosa, whose densities increased with solidity of substrate (pneumatophore-rack-rock). The other seven species Bembioium auratum^ Che zaemaea flammea^ Notirus orenatus^ Perinereis amhlyodonta^ Bocoavdia sp., Sesarma erythrodaotyla and Elminius modestus were fairly uniformly present in all six communities. With regards latitude the Siphunculida and Nemerteans were restricted to Wallis Lake. Hence, "biological species" comparisons do yield some useful information in community studies but such data are not definitive. In sinranary mathematical and statistical critera clearly show that oyster communities are influenced by the type of substrate such that species richness, diversity and species density are all greatest for rock oyster communities versus oyster communities on mangrove pneumatophores and on oyster racks. That the rock surface is exposed to a greater tidal fluctuation than the other two substrate is a probable explanation for this phenomenon. If the oyster communities be examined with regard to differences in latitude then in general terms the more northern the community the greater its species richness and diversity. In statistical terms there are significant differences between communities from different substrates but not from similar substrates from different localities. Using biological criteria oysters from the more northern locality tend to be larger and with greater body to to shell weight ratios. As larger oysters produce larger crevices which are better habitats for animals living in oysters than are smaller crevices from smaller oysters then there is a second explanation for the phenomenon described in the preceding paragraph. Finally, there appears to be little gained from an examination of the actual species in oyster communities other than: (iv) sipunculids and nemerteans do not occur in the southern communities, (ii) Amphineura and fish only were recovered from rock surface oysters, (iii) the bivalve L, australis and the polychaete G, oaespitosa were the only two animals to show any relationship between density and substrate in that they both became more numerous as the substrate became more solid. o Size E 0) o Categories U 100^ 03 m Cn M C 'H m -H 4J U > flow on oyster communities. Water flow affects the settlement, growth, feeding, excretion, dispersion etc. of barnacles on solid substrates (Doochin and Smith, 1951; Smith, 1946) as well as affecting animal communities living in other substrates (Moore, 1958; O'Gower and Wacasey, 1967; William and Smith, 1972), for example, the distribution and abundance of many benthic animals (O'Gower and Wacasey, 1967; Stephenson et al,^ 1970). To determine whether water flow affected oyster community structure, oyster samples of known ages (one and two year old cultivated oyster racks) were collected from slow and fast moving waters (18.47 and 43.47 ft/min. respectively) in Wallis Lake and the communities examined and the data analysed. The oysters themselves were first examined to determine the effects of age and of water movement on the numbers and percentage tissue dry weight of the seven size categories. From figure 18 it appears that in terms of numbers these are more smaller animals in fast flowing water than in slow flowing water for both younger and older oysters (one and two year old). The same applies for tissue weights for younger oysters, but for older oysters it appears that the larger size categories are more numerous than smaller size categories in communities from faster water than in communities from slower water. It could be inferred from these data that slower moving water favours the growth of oysters. If this trend could be substantiated in the field by experimentation it could be of some interest to the oyster industry, but this trend is not particularly Figure 19. Tissue/shell weight ratios of seven size categories of oysters from racks of varying ages in slow and fast moving water at Wallis Lake. .10. o SIZE CATEGORY 1 2 .09 3 4 • 5 .08 A ..6 X 7 .07 . a:< •06 X o UJ .05 UJ •OA CO LxJ ZD .03 tn CO .02 MEAN : 034 .01 Oj I 1Y 2Y 3Y 1Y 2Y ( FAST WATER ) (SLOWER WATER) TABLE 13 Number of species, number of individuals and index of diversity for one, two and three year old oysters from slow and fast water in Wallis Lake. Water Flow Age No. Species No. Indiv. Diversity 1 yr. 9 179 1.54 FAST 2 yr. 13 292 2.11 3 yr. 16 433 2.47 1 yr. 16 292 2.64 SLOW 2 yr. 23 637 3.41 TABLE 14 Numbers of species (N>10%), by Phylum and Class, in oyster communities from one, two and three years old racks in fast and slow water in Wallis Lake. Phylum and Class FAST s :LO W 1 yr. 2 yr. 3 yr. 1 yr. 2 yr. Annelida Polychaeta 2 2 3 3 2 Platyhelminthes - - 1 1 2 Arthropoda Crustacea 4 4 5 6 10 Mollusca Gastropoda 2 3 4 1 1 Bivalve 1 1 2 4 4 Nemerteans - - 1 1 2 Pisces - 3 - - - TW marked in figure 19 where the regression of age/water movement or tissue/still weight ratios is only slightly off the horizontal. What about the communities associated with such oysters? From Table 13 it is apparent that the numbers of both species and individuals of oyster communities are greater in the slow moving water than in the faster moving water, for both one and two year old oysters. In fact, two year old oyster communities in slow water are more diverse and dense than three year old oyster communities in fast water. Examination of Table 14 shows that crustaceans and bivalve molluscs accound for these differences. It could therefore be deduced that bivalves including oysters are better adapted to slow moving water than are gastropod molluscs which are adapted to faster moving water, however, in the case of the gastropod molluscs most of the species are commonly found on the sea shore where water if low can be extremely fast from wave action. Whether the fast moving waters affect larval settlement is not known, but most of the gastropod molluscs in the "fast communities" were adult, indicating larval settlement was not involved in the distribution and abundance of this zoological taxon. Finally as the rates of flow of water across the "fast" and "slow" communities are cyclic, because water flow is the result of tidal currents, it seems probable that the community structures in oysters are related to rate to water flow as it affects metabolic processes (feeding etc.) rather than larval settlement. TABLE 15 Percentage composition of the dominant species in oyster communities of different ages from slow and fast flowing water. Percentage Composition WATER AGE 11-20 21-30 31-40 40 + Slow 1 yr. Boaaardia P. amhlyodonta B, amphitp-ite Slow 2 yrs, Boooardia B. amphitrite Melita 1 yr. B. awfatum Fast 2 yrs, F, amarus B, amphitrite E. modeetus 3 yrs, E, modeoluB M, edulis Boooardia P. amhlyodonta B. auratum As to be expected older oyster communities were more diverse and dense than younger oyster communities (see table 13). Barnacles are dominant in most communities (Table 15) and obviously the presence of this zoological taxon is the result of larval settlement. None of the predaceous molluscs recorded in the Appendix were found on any of the oyster rack communities, irrespective of the age of the community or of the rate of flow of the water bathing the oysters. Analysis of variance for the nine common species in the oyster communities showed virtually no significant variation in density in relation to either age of the oyster racks or the rate of water flow across them, except that the polychacte Ferineveis amhlyodonta was significantly more dense in oyster communities from slower flowing waters (F = 21-51, P<0.05). Consequently, although species densities did not differ significantly, community densities and diversity were significantly greater in slower flowing waters than in faster flowing waters. This finding is the direct antithesis to that found by O'Gower and Wacasey (1967) for the benthic fauna near Miami, Florida, but nearly all of the bivalve molluscs examined by these authors were denser in the 'felower water habitat". It is therefore concluded that oysters (and bivalves) grow better in slower moving water than they do in faster moving water and they support more diverse and denser communities in the slower flowing waters. As to be expected older oysters support more diverse and denser communities than do younger oysters, but it is surprising that one-year-old oysters from slow flowing water support communities which are as diverse and almost as dense as the communities supported by three-year-old oysters. The implications of these findings to the oyster industry are obvious and the apparent trends indicated above should be more fully examined. 4.7 Effect of salinity on oyster communities. Salinity is one of the most important environmental factors affecting the estuarine fauna, as within an estuary the salinity varies from that of sea water to fresh water in the upper reaches of the estuaries fed by rain water. Salinity effects may be due to osmotic stress or they may affect specific gravity control, but osmotic stresses imposes the greater strain on estuarine organisms (Moore, 1958). Gunter (1950) states "the fauna of brackish water is marine and is not derived from fresh water. As the water becomes fresh along the salinity gradient certain invertebrates that cannot tolerate lowered salinity drop out of the picture, but some persist. There is no compensating increase in the number of species by invasion of species from fresh water and therefore the number of species in water of low salinity is low, but those present are marine." Percival (1929), Gunter (1950), Whittaker and Fairbanks (1958), Wells (1961), Hughes and Thomas (1971), and Nesvell (1971) have studied the influence of salinity on estuarine and littoral organisms and Wells (1961), when studying the fauna of oyster beds in North Carolina, reiterated these findings thus "The number of species decreased in a regular fashion from the river mouth to the TABLE 16 Numbers of species and of individuals and indices of diversity of oyster communities from three localities in Sydney Harbour over two years. STATISTIC Locality Year NO. Species No. individ. < Willoughby Bay 1972 27 4288 3.11 1973 26 4225 2.99 Fisher Bay 1972 38 2546 4.72 1973 35 2641 4.32 North Head 1972 34 5573 3.83 1973 36 6317 4.00 TABLE 17 Numbers of species by Phylum and Class in oyster communities from three localities in Sydney Harbour over two years. PHYLUM/ 19 7 2 19 7 3 CLASS W.B. F.B. N.H. W.B. F.B. N.H, 1 Coelenterata, Actinozoa 1 1 - - 1 1 Annelida, Polychaeta 5 8 6 5 6 5 Platyhelminthes, Trematoda 1 1 - 1 1 1 Phoronida 1 1 1 1 1 1 Siphunculida . 1 1 - 1 1 - Nemertea 3 3 1 4 2 3 Arthropoda, Crustacea 6 8 7 7 7 6 Mollusca, Amphineura - 2 4 - 3 3 Gastropoda 5 7 11 3 8 13 Bivalve 4 4 4 4 3 3 Echinodermata, Asteroidea - 1 - - 1 - TABLE 18 Species exclusive to oyster communities at related localities in Sydney Harbour. LOCALITY TAXA NORTH HD. NORTH HD. & FISHER B. FISHER B. WILLOUGHBY FISHER B. WILLOUGHBY B. BAY. Aoiphineura L. gaimardi Aoanthoohitona sp. - - - S. septentriones Gastropcxia B. auratum M. rrm^ginatba - - - P. BubrmmoTata M. oonoidea • SiphortaHasp. Crustacea T. purpurasoens I. quadrivalvia - B. amphitvite S. quayana C, antennatus S. erythrodaatyla Asteroidea p. exigua TABLE 19 Percentage composition of the dominant species in oyster communities at selected localities in Sydney Harbour. Percentage Composition Locality Year 11-20% 21-30% 31-40% 40% + Willough. B. 1972 B. amphitrite E. modestus 1973 Boacavdia E. modestus S. quoyana C. flammea B. auratum Fisher Bay 1972 B. auratum E. modestus 1973 E. modestus '. aaespitosa B. auratum North Head. 1972 G. aaespitosa L. australia 1973 G. aaespitosa L. australis most upstream station". The present study in Sydney Harbour found a dramatic decrease in"species diversity of the oyster community at Willoughby Bay .compared with those at North Head and Fisher Bay (see Table 16). While it is possible this decrease is associated with urban run-off at Willoughby Bay, the low densities of these communities would not support this alternative (Table 16), as high detrities loads usually increase benthic density while decreasing benthic diversity (Nitta, 1971), and they favour polychaetes, whose species numbers (Table 17) do not differ significantly in the three localities, but there is the expected increase in the number of gastropod species from Willoughby Bay to North Head (Table 17). In terms of species richness and diversity the oyster communities of Willoughby Bay differ markedly from the similar oyster communities at Fisher Bay and North Head (Table 16). In terms of density the North Head community greatly exceeds the Fisher Bay and Willoughby Bay communities, but there is no apparent explanation for the difference in community densities of the Fisher Bay and Willoughby Bay communities (Table 16), unless the urban run-off detritis of Willoughby Bay encourages density. The dominant position of the filter- feeding barnacle Elminius modestus in the Willoughby Bay and Fisher Bay communities in contrast to the dominant portions of the filter-feeding bivalve tasaea australis and the polychaete Galeolaria oaespitosa (Table 19) reflects the effects of water movement rather than the effects of salinity or estuarine communities. TABLE 20 "F" values and probabilitie.s for compasions of densities of 14 species common to oyster communities from three localities in Sydney Harbour. SPECIES COMPARISON D.F. Boaaardia sp. Between localities 1.4 7. 25 0. 10 Between years 2.3 0. 38 0. 50 Eulalia sp. Between localities 1.4 5. 03 0. 10 Between years 2.3 0. 64 0. 50 G, oaeapitoaa Between localities 1.4 71. 93 <0. 005 Between years 2.3 0. 05 0. 75 Lepidodontua sp. Between localities 1.4 99. 87 <0. 001 Between years 2.3 0. 05 0. 75 P. amblyodonta Between localities 1.4 5. 41 0. 10 Between years 2.3 • 0.6 1 0. 50 Syllia sp. Between localities 1.4 1. 05 0. 30 Between years 2.3 3. 43 0. 20 E* modeatua Between localities 1.4 17. 72 0. 05 Between years 2.3 0. 21 0. 75 A. obtuaa Between localities 1.4 52. 34 <0. 005 Between years 2.3 0. 05 0. 75 B. auratum Between localities 1.4 11. 10 <0. 05 Between years 2.3 0. 25 0. 75 C. flammea Between localities 1.4 8. 28 <0. 05 Between years 2.3 0. 38 0. 05 P. patelloidea Between localities 1.4 142. 06 <0. 001 Between years 2.3 0. 00 0. 90 L. auatralia Between localities 1.4 105. 05 <0. 001 Between years 2.3 0. 03 0. 75 M. ptanulatua Between localities 1.4 4. 82 0. 10 Between years 2.3 0. 26 0. 75 N. orenatus Between localities 1.4 5. 99 >0. 05 Between years 2.3 0. 08 0. 75 Examinations of exclusive species in the North Head and Fisher Bay oyster communities as compared with the Willoughby Bay oyster community (Table 18) confirms the conclusions that the Willoughby Bay community differs markedly from the other two communities and that these latter two-communities share very similar species compositions Applying analysis of variance between the densities of selected species from the oyster communities at North Head, Fisher Bay and Willoughby Bay during 1972 and 1973 gave significant values only between localities and not between years (Table 20). Of the 14 species analysed eight species showed significant density differences between the three localities. These species are: Gateolavia oaespitosa polychaete Lepidodontus sp. polychaete Elminius modestus barnacle Austroooohlea obtusa gastropod Bembioium auratum gastropod Chezamaea ftammea gastropod Onohidella patelloides gastropod Lasaea australia bivalve Mytilus edulis bivalve Four of these species are filter feeders, four are gastropod grazers and the ninth is carnivorous. The typical seashore species G. oaespitosa and L. australis decrease in density quite markedly with distance from the ocean viz. B Size Categories 100 90. \ 80, 70, 60 SO J 30 20 10 0 MAY AUG NOV FEB MAY AUG NOV FEB Figure 20. Percentage number (A) and percentage dry tissue to shell weight (B) of seven size categories of oysters from oyster racks at Wallis Lake during the four seasons. North Head Fisher Bay Willoughby Bay G. oaespitosa 1978 705 48 L, austvalis 3425 131 213 and the typical estuarine species E. modestus, C, flammea and M, ^dulis show increases in density with distance from the ocean viz. North Head Fisher Bay Willoughby Bay E. modestus 23 454 1538 C. flammea 9 216 490 M. edulis 20 67 174 Consequently the variations in the oyster communities associated with locality in Sydney Harbour show marked correlations with likely variations in salinity regimes at the three selected localities, there being less diverse and denser communities in habitats with varying salinity regimes than in habitats with a constant salinity, and visa-versa. 4.8 Effect of season on oyster communities Seasonal samples of oyster communities from the untended oyster racks in Wallis Lake were made during May, August, November of 1972 and February, May, August and November of 1973 and figure 20 indicates the rhythmic variations in the size categories of the oysters in Wallis Lake. These variations differed significantly viz. F d.f. P Between seasons 12.69 4.12 <0.001 and showed a slight increase in the percentage of small oysters in Spring followed by a decrease in summer, but about the same number of spat were found in all four seasons with a slight summer decline, probably the result of summer insolation. The percentage of large oysters were the same in spring,summer and autumn, but it increased in winter. The reason for this is unknown, but it could be due to a lowered winter mortality of larger oysters. If so, then harvesting of oysters would give better economic returns in winter than during spring, but, as the ratio of tissue to shell weight was least during winter and greatest during spring, obviously further detailed studies on oyster growth under varying environmental conditions are needed to clarify some of the apparent correlations found during this community investigation. While O'Gower and Meyer (1964) showed temperature,, desiccation and wave-action to be the main factors influencing seasonal variations in littoral gastropods on the ocean shore, wave-action does not influence oysters inside estuarines and as oysters are cultured on horizontal racks in the mid tide zone then desiccation , insolation and temperature are the major factors influencing seasonal variation in the oyster communities. In all communities there is a more or less constant process of partial or complete denudation of the flora and fauna with subsequent replacement by recruitment or migration (Moore, 1958), and with large scale denudation as long as three to four years may pass before recruitment and migration have made up this loss (Moore and Sproston 1940; Knight and Parke, 1950). In Table 21 the species richness of the Wallis Lake oyster community fell from 21 species in August to 15 in November and did TABLE 21 Numbers of species, numbers of individuals and indices of diversity for oyster communities over the seasons {Wallis Lake). YEAR SEASON NO. SPECIES NO. INDIVID. DIVERSITY 1972 May 20 598 2.97 August 21 649 3.08 November 15 668 2.15 1973 February 18 801 2.54 May 18 673 2.61 August 20 977. 2.76 November 21 1070 2.87 TABLE 22 Numbers of species by Phylum and Class in oyster communities over the season (Wallis Lake). 19 7 2 1 9 7' 3 T A X A MAY AUG. NOV. FEB. MAY AUG. NOV Polychaeta 3 4 2 2 2 3 3 Trematoda 1 - - - 1 1 1 Phoronida - - - - - 1 1 Actinozoa - 1 - 1 1 1 1 Nemertea - 1 2 - - 1 1 Crustacea 8 8 5 7 6 6 7 Gastropoda 2 4 3 3 3 4 4 Bivalve 4 3 3 3 3 3 3 Pisces 2 - - 2 2 - - TABLE 23 Percentage composition of the dominant species in oyster communities over the seasons (Wallis Lake). PERCENTAGE COMPOSITION YEAR SEASON 11-20 21-30 31-40 40+ May B. auratum Boaoardia - - C.. flammea 1972 Melita sp. P. amblyodonta Aug, B. amphitritus P. amblyodonta Boaoardia sp. Nov. B. auratum Boaoardia sp. C. flammea P. amblyodonta Feb. B. auratum Boaoardia sp. — C. flammea May B, auratum Boaoardia sp. f C. flammea Melita sp. Aug. B. auratum C. flammea Boaoardia sp. anemones Nov. B. auratum C. flammea Boaoardia sp. E. modestus TABLE 24 "F" values and probablities for coitiparisions of densities of 12 species common to oyster communities varying with season (Wallis Lake}. SPECIES COMPARISON D.F. F P Boaaavdia sp. between seasons 1.4 5.56 0.10 between years 2.3 0.01 0.75 P. amblyodonta between seasons 1.4 0.29 0.50 between years 2.3 7.70 0.10 B. amphitrite between seasons 1.4 3.93 0.10 between years 2.3 . 0.22 0.75 E. modeatus between seasons 1.4 1.79 0.25 between years 2.3 0.80 0.50 Melita sp. between seasons 1.4 32.85 <0.01 between years 2.3 0.10 0.75 5. erythrodaotyla between seasons 1.4 1.63 0.25 between years 2.3 0.04 0.75 B. auratum between seasons 1.4 1.39 0.25 between years 2.3 0.97 0.25 C. flammea between seasons 1.4 0.67 0.25 between years 2.3 3.05 0.10 L. aoutispira between seasons 1.4 1.56 0.25 between years 2.3 0.12 0.75 L. australie between seasons 1.4 6.27 0.10 between years 2.3 0.05 0.75 M. edulis between seasons 1.4 0.44 0.50 between years 2.3 2.55 0.10 N. arenatus between seasons 1.4 21.40 <0.05 between years 2.3 0.04 0.75 not reach its original value until the following November. It is therefore apparent that species richness did not fluctuate cyclically, but that there was a minor catastrophic reduction in species richness during February 1972 and that the community recovered after a year. From Table 22 it seems that the Crustacea suffered most from this reduction and as most of the Crustacea in the community are mobile, it seems likely that migration rather than recruitment was the means by which community species richness was restored. The significantly larger numbers of individuals during August/November in 1973, as against the values for the corresponding months in 1972, indicate that the crustacean species which suffered from the minor catastrophic denudation were not major constituents of the community. That is, from August to November 1972 the numbers of species fell from 21 to 15 and the numbers of individuals rose from 649 to 668, whereas from August to November 1973 the numbers of species rose from 20 to 21 and the numbers of individuals rose from 971 to 1070. Thus in both years the increases in the numbers of individuals from August to November were of the same order. Of the twelve species common through all the seasons only two species Melita species, anamphipod and Notivus orenatus, a bivalve, varied significantly in density over the seasons, but none of the species varied between the years (Table 24). The percentage composition for dominant species in the oyster communities showed the polychaete Boooardia species to fluctuate seasonally from 21-30% of the community in May 1972, 31-40% • " August 1972, 21-30% ' " November 1972, 21-30% ' " February 1973, 11-20% ' " May 1973, 11-20% ' " August 1973, 31-40% ' " November 1973. whereas the gastropod Bembicium auratum had a constant percentage composition of 11-20% over nearly all of the seasons sampled. The numbers of individuals of these two species over the seasons were: May Aug. Nov. Feb. May Aug. Nov. S. auratum 66 42 128 101 122 122 116 Boooandia sp. 148 228 198 218 91 129 329 showing B. auratum density to be relatively constant except for May and August 1972, whereas the density of Bocoavdia sp. showed a cyclic decrease during May and a significantly lower November 1972 density than the November 1973 density. From all of the above only a few definite conclusions may be reached: first there was an apparent increase in the percentage of large oysters during winter but the shell tissue weight ratio for winter oysters was lower than for the rest of the seasons. Second the seasonal variations in species richness indicated a heavy mortality of low density species, predominantly crustaceans occurred during the summer of 1972. Third there was no apparent cyclic variations in either species richness or community density. Finally these seasonal studies showed that continual studies on seasonal variations of both oysters and their communities would return data which could be extremely useful to the oyster industry. 5.0 Summary and Conclusions 1. Oyster communities from Wallis Lake, Sydney Harbour and Jervis Bay were studied and quantitative analyses made to determine the effects of latitude, substrate, age of community, salinity and seasonal variations on the density and diversity of the communities. 2. Most of the positive associations of species in oyster beds are due to their similar microhabitat requirements which provide shelter from insolation, desiccation, water movement and temperature, but it is not thought likely that any of these positive associations are due to predator/prey relationships. 3. Mathematical and statistical criteria show oyster communities to be influenced by the type of substrate such that diversity and density are greatest in rock oyster communities, next for oysters on mangrove pneumatophores and least on oyster racks. That rock surfaces and pneumatophores are exposed to the full tidal range whereas oyster racks have limited tidal exposure is certainly correlated with the observed differences. 4. In general the more northern the oyster community the greater is its diversity while the more STDU±hern the oyster the larger it is and the greater its body weight to shell weight ratio. 5. Older oysters support more diverse and dense communities than do younger oysters and oysters in slower moving waters are larger and support more diverse and dense communities than are/do oysters in faster flowing waters. 6. Oysters from localities exposed to salinity variations support denser but less diverse communities than oysters from localities of constant salinity. 7. Seasonal variation in diversity and density of oyster communities show little or no cyclic changes, but there was a heavy mortality of low density species in the community during the summer of 1972. It seems that winter oysters are longer but have lower body weight to shell weight ratios. 8. These limited studies clearly indicate that continued examination of oysters and their communities could yield information useful to the oyster industry. LITERATURE CITED Bennett, I. and Pope, E.G. (1953). Intertidal zonation on the exposed rocky shores of Victoria, together with a rearrangement of the biogeographical provinces of temperate Australian shores. Aust. J. mar, freshw. Res., 4 : 105-59. Brillouin, L. (1960). Science and Information Theory. 2nd Ed. New York, Academic Press. Brooks, W.K. (1891). The Oyster. Johns Hopkins Press, Baltimore. Bugas, M.A. and Gibson, T.G. (1969). Species diversity: benthonic foraminifera in western North Atlantic. Science, 163 : 72-75. Gaspers, H. (1950). Die Lebensgemeinschaft der Helgolander Austernbank. Helgoland. Wiss. Meeresunters, _3 : 119-169. Gox, J.G. (1883). On the edible oysters found in the Australian and neighbouring coasts. Proc. Lin. Soc N.S.W., 7(1) : 122-33. Ghapman, G. (1949). Thixotropy and dilatancy of marine soil. J. mar, biol. Assoc. U.K., ^(1) : 123-140. Granfield, H.J. (1968). An unexploited population of oysters, Ostrea lutaria Hutton, from Foveaux Strait. II. Larval settlement patterns and spat mortality. N.Z. J. marine freshw. Res., 2(2) : 183-203. Dahl, E. (1960). Some measures of uniformity in vegetation analysis. Ecology, 41 : 805-808. Dakin, W.J., Bennett, I. and Pope, E.G. (1952). Australian Seashores. Angus & Robertson, Sydney. Dame, R.F. (1972). The ecological energies of growth, respiration and assimilation in the intertidal American oyster Cvassostrea virginica. Mar. Biol., 11_ : 243-250. Davis, B.N.K. (1963). A study of micro-arthropod communities in mineral soils near Corby, Northauts. J. anim. Ecol. , ; 49-71. Dean, B. (1890) . The physical and biological characteristics of the natural oyster grounds of South Carolina. Bull. U.S. Fish. Comm., 1890 X : 335-361. Debauche, H.R. (1962). The structural analysis of animal communities of the soil. Progress in soil zool. Vol. 1 (Ed. Murphy), 10-25. De Benedictis, P.A. (1973). On the correlation between certain diversity indices. Am. Nat., 107 : 295-302. Dehnel, P.A. (1955). Rates of growth of gastropods as a function of latitude. Physiol. Zool., 28 : 115-144. Dice, L.R. (1952). Natural communities. Uni. of Michigan Press. Doochin, H. and Smith, F.G.W. (1951). Marine boring and fouling in relation to velocity of water currents. Bull, mar, sci. Gulf and Caribbean, 1(3) : 196-208. Elton, C. (1927). Animal Ecology. Sidgwick and Jackson, London. Endean, R, Kenny, R, and Stephenson, W. (1956). The ecology and distribution of intertidal organisms on the rocky shores of the Queensland mainland. Aust. J. mar, freshw. Res., 7 : 88-146. Fager, E.W. (1957). Determination and analysis of recurrent groups. Ecol., 38 : 586-95. TT Fager, E.W. (1963). Communities of organisms. Chapt. 19 in Hill, M.N. Ced) The Sea, Vol. 2, John Wiley & Sons, Inc. New York. Filice, F.P. (1954). A study of some factors affecting the bottom fauna of a portion of the San Francisco Bay estuary. Wasmann Jour. Biol., 12 : 257-292. Filice, F.P. (1958). Invertebrates from the estuarine portion of San Francisco Bay and some factors influencing their distribution. Wasmann Jour. Biol., U : 159-211. Fisher, R.A., Corbett, A.S. and Williams, C.B. (1943). The relation between the number of species and the number of individuals in a random sample of an animal population. J. anim. Ecol. 12 : 4 2-58. Fleming, C.A. (1952). A Foveaux Strait oyster bed. N.Z. J. Sci. & Technol. Sept., B., 34 : 73-85. Frey, D.G. (1946). Oyster bars of the Potomac River. Fish and Wildl. Ser. Spec. Sci. Rept. 32 : 1-93. Gilbert, C.H. (1899). Reports upon certain investigations relating to the planting of Oyster in Southern California. Bull. U.S. Fish. Comm. 1899, Vol. 9 : 95-98. Grave, C. (1905). Investigations for the promotion of the oyster industry of North Carolina. Rep. U.S. Comm. Fish., ^ : 247-341. Grisebach, A. (1938). Ueber den Einfluss des Climas auf die BegrSngung der natiirlichen Floren. Linnea, 12 : 159-200. Guiler, E.R. (1950). The intertidal ecology of Tasmania. Pap. Roy. Soc. Tasm. 1949(1950) : 135-201. w Guiler, E.R, (1960) . The intertidal zoner^forming species on rocky shores of the east Australian coast. J. of Ecol., £8 : 1-28. Gunter, G. (1950) . Seasonal population changes and distributions as related to salinity of certain invertebrates on the Texas coast, including commercial shrimps. Publ. Inst. Mar. Sci., ]^(2) : 117-189. Hopkins, S.H. (1957). Oysters. Treatise on Mar. Ecology and Paleoecology. Geol. Soc. Amer. Mem. £^(1) : 1129-1134 Hughes, R.N. and Thomas, M.L.H. (1971). Classification and ordination of benthic samples Bedaque Bay, an estuary in Prince Edward Island, Canada. Mar. Biol., : 227-235. Humboldt, Al. de (1805). Essai swe la geographie des plantes: accompagne d'um tableau physique dis regions e'quinoxiales. Paris: Levrault, Schoell et cie. Iredale, I. and Roughley, T.C. (1933). The scientific name of the commercial oyster of New South Wales. Proc. Linn. Soc. N.S.W., 58 : 278. Isham, L.B., Moore, H.B. and Smith, F.G.W. (1951). Growth rate measurement of shipworms. Bull, mar. Sci. Gulf and Caribbean, 1(2) : 136-147. Jaccard, P. (1912). The distribution of the flora in the alpine zone. New Phytol., 11 : 37-50. Knight, M. and Parke, M.W. (1950). A biological study of Fuous vesiculosus L. and F. serratus L. J. mar. Biol. Assoc. U.K., 2^(2) : 439-514. Kohn, A.J. (1968). Microhabitats, abundance and food of Conus on atoll reef in the Maldire and Chagos Islands. Ecology, 49 : 1046-1061. Kontkanen, P. (1957). On the delimitation of communities in research on American Biocoenotics. Cold Spring Harbor Symp. on quantitative Biology. 22 : 373-378. Korringa, P. (1951). The shell of Ostrea edulis as a habitat. Arch. Neerl. Zool., 10 : 32-135. Loya, Y. (1972). Community structure and species diversity of hermatypic corals at Eilat, Red Sea. Mar. Biol., 13 : 100-123. McDermott, J.J. (1960). The predation of oysters and barnacles by crabs of the Family Xanthidae, Proc. Pennsylvania Acad. Sci., 34 ; 199-211. Mcintosh, R.P. (1967) . An index of diversity and the relation of certain concepts to diversity. Ecology, 48 : 392-404. MacArthur, R.H. (1957). On the relative abundance of bird species. Proc. natn. Acad. Sci. U.S.A., 43 : 293-295. MacDonald, H.J. (1940). Animal associates of oysters at Beaufort, North Carolina. M.A. Thesis, Duke University. Maclntyre, R.J. (1959). Some aspects of the ecology of Lake Macquarie N.S.W, with regard to an alleged depletion of fish. VII. The benthic macrofauna. Aust. J. mar, freshw. Res., ^ : 341-343. Malcolm, W.B. (1971). The Sydney rock oysters. Aust. Nat. Hist. , ^(2) : 46-50. Margalef, R. (1951). Diversidad de especies en las communidades naturales. Proc. Inst. Biol. Apt., : 5. Mattox, N.T. (1949). Studies on the biology of the edible oyster: Ostrea rhigoporae Guilding, in Puerto RicoJ Ecol. Monogr. 19 ; 339-356. "W Menzel, R.W. and Hopkins, S.H. (1954). Studies on oyster predators in Terrebonne Parish, La. Taxas. A & M Res. Found. Proj. Rept., 19 ; 1-145. Menzel, R.W. and Nichy, F,E. (1958) . Studies of distribution and feeding habits of some oyster predators in Alligator Harbour, Florida. Bull, mar. Sci. Gulf and Caribbean, 8(2) : 125-145. Meyer, G.R. and O'Gower, A.K, (1963). The ecology of six species of gastropod molluscs. Associations between species and association with wave action. Aust. J. mar, freshw. Res., 14 : 176-93. Mistakidis, M.N. (1951). Quantitative studies of the bottom fauna of Essex oyster grounds. Fishing Invest, (ser. 2) , ^(6) ; 1-47. Mobius, K. (1877). The oyster and oyster culture. (Translated by H.J. Rice from Mobius 1877) : Report U.S. Comm. Fish., 8 : 683-752 (1883). Monk, C.D. (1967). Tree species diversity in the eastern deciduous forest with particular reference to north central Florida. Amer. Nat., 101 : 173-187. Moore, H.B. (1935). The biology of Balanus balanoides. Part IV. Relation to environmental factors. J. mar, biol. Assoc. U.K., 3^(2) : 869-885. Moore, H.B. (1958). Marine Ecology. John Wiley & Sons, New York Moore, H.B. and Kitching, J.A. (1939). The biology of Chthamalus stellatus (Poli). J. mar, biol. Assoc. U.K., 22(2) : 521-541. Moore, H.B. and Sproston, N,G. (1940), Further observations on the colonization of a new rocky shore at Plymouth. J. anim. Ecol., 9(2) : 319-327, Moore, H.F. (1910). Condition and extent of the oyster beds of James River, Virginia. Report U.S. Comm. Fish., 88 pp. Mountford, M.D. (1962). An index of similarity and its application to classificatory problems. Progress in Soil Zoology, Vol. 1 (Ed. Murphy) 43-50 Lond. Newton, L. and Cribb, A.B. (1951). Some aspects of algal ecology in Britain and Australia. Research, £ : 449-55. Nichy, F.E. (1956). The effect of predators on the mortality of oysters in a high salinity area in Florida. Unpub. Master's Thesis, Florida State University, Tallahassee, 84 pp. O'Gower, A.K. and Meyer, G.R. (1964). The ecology of six species of littoral gastropod molluscs. II. Seasonal variations in the six populations. Aust. J. mar, freshw. Res., 16 : 205-218. O'Gower, A.K. and Meyer, G.R. (1971). The ecology of six species of littoral gastropods. III. Diurnal and seasonal variations in densities and patterns of distribution in three environments. Aust. J. mar, freshw. Res., 22 : 35-40. O'Gower, A.K. and Wacasey, J.W. (1967). Animal communities associated with Thalassia^ Biplanthera and sand beds in Biscayne Bay. Analysis of communities in relation to water movements. Bull. Mar. Sci. in Gulf and Carib., 17(1) : 175-210. Oosting, H.J. (1956). The study of plant communities. 2nd Edition. W.H. Freeman and Co., San Francisco & London. Pearse, A.S. and Wharton, G.W. (1938). The lyster 'leech', Styloohus inimious Palombi, associated with oysters on the coasts of Florida. Ecol. Monogr., 8 : 605-655, Pearson, K. C1904), On the theory of contingency and its relation to association and normal correlation. Drapers Co. Res. Mem, Biometric Ser. I, Percival, E. (1929). A report on the fauna of the estuaries of the River Tamar and River Lynher. J. mar, biol. Assoc. U.K., 16 : 81-108. Pielou, E.G. (1966b). Shannon's formula as a measurement of specific diversity. Its use and misuse. Amer. Nat. , : 463-465. Pope, E.G. (1945). A simplified key to the sessile barnacles found on the rocks, boats, wharf piles and other instalations in Port Jackson and adjacent waters. Rec. Aust. Mus. Vol., ^(6) : 351-372. Preston, F.E. (194 8). The commoness and rarity of species. Ecology, 29 : 254-283. Roughley, T.G. (1922). Oyster culture on the George's River, New South Wales. Tech. Educ. Ser. Tech. Mus. Syd. ^ : 1-69. Roughley, T.G. (1926). An investigation of the cause of an oyster mortality on Georges River, N.S.W. 1924-25. Proc. Linn. Soc. N.S.W., 5j^(4) : 446-91. Roughley, T.G. (1928). On the dominant species of the genus Ostrea. Nature, 122 : 476-7. Roughley, T.G. (1933). Life history of the Australian oyster : Ostrea commevcialis, Proc.-Linn. Soc, N.S.W,, 58 : 279-333. TUT" Sager, P.E. and Easier, A.D. (1969). Species diversity in locustrine phytoplankton. 1. The components of the index of diversity from Shannon's formula. Amer. Nat., 103 : 51-59. Simpson, E.H. (1949). Measurement of diversity. Nature, Lond. 163 : 668. Simpson, G.G. , Roe, A. , and Lewontin, R.C.(1960) . Quantitative Zoology. Harcourt Brace. Shannon, C.E. and Weaver, W. (1963) . The mathematical theory of communication Urbana. Uni. of Illinois Press. Smith, F.G.W. (1946). Effect of water currents upon the attachment and growth of barnacles. Biol. Bull. 9£(1) : 51-70. S0rensen, T. (1948) . A method of establishing groups of equal amplitude in plant sociology based on similarity of species content and its application to analysis of vegetation of Danish common. Biol. Skr,, _5 : 34. Stephenson, T.A. and Stephenson, A. (1952). Life between the tide-marks in North America. II. Northern Florida and Carolina. J. Ecol. 40 : 1-49. Stephenson, W. and Williams, W.T. (1971). A study of the benthos of soft bottoms, Sek Harbour, New Guinea, using numerical analysis. Aust. J. mar, freshw. Res., 22 : 11-34. Stephenson, W., Williams, W.T., and Lance, G.N. (1970). The macrobenthos of Moreton Bay. Ecol, Monogr., 40 : 459-494. Thomson, J.M. (1950). The effect of orientation of culture material on the setting of the Sydney rock oyster. Aust. J. mar, freshw. Res., 1 : 139-154. Thomson, J.M. (1952). The acclimatization and growth of the Pacific oyster {Eryphaea gigas) in Australia. Aust. J. mar, freshw. Res., • 64-73. Thomson, J.M. (1953). The general of oysters and Australian species. Aust. J. mar, freshw. Res., ^ : 132-168. Webb, W.L. (1950). Biogeographic regions of Texas and Oklahoma. Ecol., 31 : 426-433. Wells, H.W. (1961). The fauna of oyster beds, with special reference to the salinity factor. Ecol. Monogr., 3(3) : 239-266. Whittaker, R.H. (1965). Dominance and diversity in land plant communities. Science, N.Y., 147 : 250-260. Whittaker, R.H. and Fairbanks, C.W. (1958). A study of plankton copepod communities in the Columbia Basin, Ecol., 39. • 46-65. Williams, C.B. (1947). The logrithmic series and comparison of island floras. Proc. Linn. Soc. Lond., 158 : 104-108. Williams, C.B. (1964). Patterns in the Balance of Nature. Academic Press (London). Williams, W. and Smith, K. (1972). Growth of the bay scallop : The influence of experimental water currents. J. expt. mar. Biol. Ecol., ^ : 7-18. Wilson, D.P. (1939). The influence of the substratum on the metamorphosis of Notomastus larvae. J. mar, biol. Assoc. U.K., 22(1) : 227-243. APPENDIX 1 Oyster communities at Wallis Lake, Sydney Harbour and Jervis Bay. LOCALITY SPECIES Wallis L. Sydney H. Jervis B. Coelenterata species A Platyhelminthes species A species B species C Sipunculida species A Nemertinea species A species B species C species D Phoronida species A Annelida Booaardia sp. Cirviformia tentaaulata CirratuluB sp. Dorvillea sp. Eulalia sp. Galeolavia oaeepitoea Uaplosaoloploa sp. Lepidonotua sp. Nereis peroniensia Perinereis ambtyodonta Sabellid sp. Syllie sp. Arthropoda Balanue amarytlia Balanua amphitite Chthamalia antennatus Elminiua modestus Ibla quadrivalvis Tetraolita purpurasaena Chelura tevebrana Corophium af, nobile Deto mafia Gammaridae sp. Lais pubeaaens Ligia exotica Melita sp. raratanaia ignatua Photia af. brevioaudata Sphaeroma quoyana Talitvoidea sp. Alpheua elliptica Eriooheir apinoaua LOCALITY SPECIES Wallis L. Sydney H. Jervis B, Leptograpaus variegatua Paragrapsua laevie Pilumnus monilifev Seaarma erythvodaatyla Mollusca Aaanthoahitona sp. Liolophura gaimardi Notoplax sp, Sypharoohiton aeptentrionea Auatroooohl&a obtuaa Bedeva hanleyi Bemhioium auvatum Celtana tramoaerioa Chezaemaea flammea Littorina aautiapira Littorina unifaaoiata Melanerita melanotragua Montfox'tula aonoidea Morula marginalha Naaaapiua buahardi Notoasmaea petterdi Onohidella patelloidea Onahidium anobiua Ophicardellua sp. Patelloidea altiooatata Patelloidea latiatrigata Patelloidea aubmarmorata Pseudoliota sp. Siphonaria dentiaulata Bavbatia sp. Fluviolanatua amarus Kellia naturda Laaaea auatralia Muaoulua variaoaua Mytilus edulis Notirua arenatua Tvichomyia hirauta Echinodermata Patiriella exigua Pisces Favonigobiua tamevenaia Omobranohua anollius Redigobius maovoetoma Waiteopsis paludia >001044401