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1.
Samples of the scleractinian coral Pocillopora damicornis were collected from six sites located around four islands in the Ryukyu Archipelago, southern Japan, and subjected to allozyme
electrophoresis. Seven polymorphic loci were examined for their allelic patterns. The ratio of observed to expected genotypic
diversity (0.30 < G
o
:G
e
< 0.64), the ratio of the observed number of genotypes to the number of individuals (0.47 < N
g
:N
i
< 0.75), and deviations from Hardy–Weinberg equilibrium indicated that asexual reproduction plays a major role in the maintenance
of established populations. However, populations were not completely dominated by a single or a few clones, and most clones
were represented by only a few individual samples. The high frequency of typhoons in the region suggests that, in P. damicornis, fragmentation caused through occasional exposure to powerful waves is a major mode of asexual reproduction, but asexual
production of planulae may also be contributing to the maintenance of populations. A significant genetic differentiation (F
ST) was found between the six populations examined (0.027 < F
ST < 0.092, average F
ST = 0.056). The moderate gene flow is discussed according to characteristics of the larval stage of the species, and to circulation
patterns in the region.
Received: 7 August 1998 / Accepted: 18 May 1999 相似文献
2.
Ophiomyxa brevirima is a direct-developing species of brittle-star found around the coast of New Zealand. The mode of reproduction of this ophiuroid
was studied using isozyme electrophoresis of mother and brooded offspring. Multi-locus assessment of the genotypes of 35 adult
females and their brooded offspring was undertaken. A minimum of 45% of broods assessed showed evidence of amictic reproduction,
with all offspring in these broods possessing genotypes that were identical to the genotype of their heterozygous mother.
In most other broods there was evidence of segregation. These observations are interpreted as evidence of both sexual and
asexual reproduction in this ophiuroid species.
Received: 19 November 1996 / Accepted: 28 January 1997 相似文献
3.
C. T. Achuthankutty Y. Shrivastava G. G. Mahambre S. C. Goswami M. Madhupratap 《Marine Biology》2000,137(1):19-22
Effect of salinity on the feeding rate and parthenogenetic reproduction of asexual females of the cladoceran Diaphanosoma celebensis Stingelin was studied. Short-term (10 h) grazing experiments were conducted using Isochrysis galbana as feed at 5, 17, 25 and 30 psu salinity. Gut pigment concentration showed a significantly higher rate of feeding at lower
salinities. Survival, growth, maturity attainment and neonate production of asexual females reared in the above four test
salinities indicated preference for lower salinities (5 and 17 psu). The mean size of adult females decreased from 909 to
593 μm, mean life span from 24 to 5 d, mean neonate production from 12 to 2 and mean size of neonates from 434 to 400 μm as
the salinity increased from 5 to 30 psu. Salinity variations also affected the size and age of primiparous females. Resting
egg formation and sexual reproduction did not occur at the tested salinities. The results indicate that D. celebensis is adapted to low saline, estuarine environments.
Received: 14 January 2000 / Accepted: 24 March 2000 相似文献
4.
The majority of published accounts on scleractinian coral reproduction are from the tropical Pacific and Caribbean, with
very little information known about Red Sea species. This report examines variation in reproductive mode in 24 species of
hermatypic corals (belonging to seven families) in the Gulf of Eilat, Red Sea. Eighteen species are hermaphroditic broadcasters,
two are hermaphroditic brooders and three are gonochoric broadcasters. In the Pocilloporidae, the gonads project into the
body cavity, while in the other six families the gonads reside inside the mesenteries. The number of gonads per polyp in broadcasting
species follows family or genus lines. Fecundity (eggs per polyp) increases with polyp size. Brooding species usually exhibit
one or two gonads per polyp and each gonad contains only one to three oocytes. Oocyte size varies widely and does not relate
to mode of reproduction. The largest oocytes (diameter = 450 μm) occur in the brooding coral Alveopora daedalea and in broadcasting species of the genus Acropora (diameter = 420 μm). Gonad morphology and gonochorism versus hermaphroditism appear to be constrained phylogenetically at
the family or genus level. Lastly, this report compares the data presented for Red Sea scleractinian species with the data
available on scleractinian corals from other geographical regions.
Received: 2 February 1993 / Accepted: 9 March 1998 相似文献
5.
Seasonal variation in reproduction and population size structure was investigated for the suspension-feeding bivalve Limopsis tajimae Sowerby inhabiting the upper bathyal zone (300 m deep) of Suruga Bay, central Japan. The bivalve was collected at 1- to 4-month
intervals for a period of 22 months, and bottom environment was monitored concurrently to detect factors affecting seasonality
in the bivalve. Bottom water temperature, organic carbon and nitrogen contents in the sediments did not exhibit seasonal variation.
Size-adjusted soft-tissue weight varied slightly, but statistically significantly between stations and months. However, its
seasonal pattern was not obvious, and the pattern of temporal variation was totally different between stations. The sex ratio
did not deviate from 1:1, and there was no significant difference between shell lengths of females and males. Females possess
both immature small oocytes and large developed oocytes in their ovaries throughout the year, suggesting that they can potentially
undergo year-round continuous reproduction. The proportion of developed oocytes in each female varied greatly from month to
month, although no seasonal cycle was obvious. Population size structure of L. tajimae was polymodal. A mode of the smallest size class occurred in most months, suggesting long periods of bivalve recruitment.
These findings indicate that seasonal variation in reproduction of the bivalve was negligible, probably reflecting constant
physical and nutritive conditions of the bottom environment.
Received: 6 January 1998 / Accepted: 19 May 1998 相似文献
6.
In the eutrophic Veerse Meer lagoon (The Netherlands) large amounts of free-floating thalli from Ulva spp. are present from May to October. In winter however, no algae seem to occur in the lagoon. Sexual reproduction appears
to be negligible, as spore formation and germling growth are observed only sporadically. Results of a field survey showed
that in winter, viable Ulva biomass is present buried in the sediment of the shallow parts of the lagoon. Freezing experiments demonstrated that the
algae are able to survive temperatures of −5 °C for 2 weeks when kept in darkness. In spring, the buried Ulva thalli are liberated out of the sediment to initiate a bloom. A field experiment indicates that bioturbation by the lugworm
Arenicola marina does not stimulate the release of the thalli. Burial and winter survival can explain the rapid increase in Ulva biomass in spring and suggest that the initial spring biomass is one of the major factors determining the maximal biomass
in summer.
Received: 28 October 1997 / Accepted: 20 January 1998 相似文献
7.
Reproduction in the sea urchin Centrostephanus rodgersii was examined in two types of habitats (“barrens”, i.e. habitats characterised by the high crustose coralline algal cover
typical of urchin-barren grounds, and by the absence of macroalgae; and “fringe”, i.e. habitats characterised by a high macroalgal
biomass and few C. rodgersii) at four locations in New South Wales. The four locations: the Solitary Islands, Sydney, Ulladulla and Eden, span the distribution
of C.␣rodgersii from the subtropics at its northern limit to temperate waters near its southern limit. Histology and estimates of gonad retrieval
rate (GRR) from January 1994 to October 1995 indicated that reproduction was synchronous at all locations. An increase in
the tempo of gametogenesis in May and onset of spawning in June at all locations is consistent with entrainment in response
to exogenous factors. Over the range studied, C. rodgersii experienced relatively similar daylength cycles and contrasting sea-temperature cycles. Short days and lunar conditions coinciding
with the solstice appear likely proximate cues for the onset of spawning. The major difference in reproduction among locations
was in the duration of spawning. In the southern parts of its range breeding occurred over a 5 to 6 mo period, whereas at
the Solitary Islands it lasted ≃1 mo. At most locations the GRRs were significantly higher in the fringe habitat than in the
barrens habitat. The lower reproductive output of urchins in the barrens habitat was attributed to the food-poor conditions
typical of this habitat. The developing fishery for C. rodgersii is likely to be most effective from March to early May. Urchins from barrens areas may not provide sufficient yield to warrant
harvesting.
Received: 29 October 1997 / Accepted: 18 May 1998 相似文献
8.
A. G. Grottoli 《Marine Biology》1999,135(3):437-449
Stable-isotope and growth records of coral skeletons are often used to reconstruct tropical paleoclimate, yet few surveys
have systematically examined the natural variability in coral skeletal 13C, 18O and maximum linear skeletal extension (MLSE) across depth. Here, interspecific, intraspecific, and geographical variations
in coral skeletal 13C, 18O, and MLSE were examined in the corals Porites compressa, P. lobata, and Montipora verrucosa grown at 1.7, 5.0, and 8.3 m depth from August 1996 to March 1997 at The Point Reef and Patch Reef #41 field sites in Kaneohe
Bay, Hawaii. Coral skeletal 13C values significantly decreased with depth and differed between species, but did not vary between field sites. 18O values were not significantly different across depth within a species, but did differ among species and field sites. High-resolution
analysis of the intra-annual variation in skeletal 13C and 18O in P. compressa at 2.0 m depth confirms that these isotopes reflect changes in solar irradiance and temperature, respectively. Changes in
MLSE across depth were consistent within, but highly variable among, species. Peak MLSE occurred at 1.7, 5.0, and 8.3 m for
P. lobata, P. compressa, and M. verrucosa, respectively. Such interspecific variation in MLSE patterns may be attributable to one or more of the following: increases
in zooplankton in the diet, changes in metabolic processes, or changes in growth form with depth. Overall, these results imply
that natural inter- and intraspecific variability in coral skeletal 13C, 18O, and MLSE should be considered when interpreting and comparing coral-based tropical paleoclimate data from various coral
species, depths, and field sites.
Received: 6 October 1998 / Accepted: 8 July 1999 相似文献
9.
Reproductive success among clonal taxa is often portrayed as a simple function of clone size, but reproduction in Pseudoplexaura porosa (Houtuyn), a common Caribbean gorgonian, reflects a more complex relationship between size and gamete production. Tagged
colonies were sampled at two reefs in the San Blas Islands, Panama during the 1995 spawning season to determine the colony
size at first reproduction, size-dependent polyp fecundities, and whole colony gonad production, and to follow the gametogenic
cycle. Additional data were obtained during non-spawning months in 1984 and 1985. Of 120 colonies ranging in height from 20
to 250 cm, only colonies taller than 50 cm were reproductive. An average of 4.33 oocytes polyp−1, 560 to 800 μm in diameter, were released during monthly synchronous spawning events from June to September. Oocytes released
each month developed from a group of intermediate size oocytes present at the end of the preceding month. Almost all oocytes
>560 μm were released during each spawning event. Spermatogenesis was a shorter process than oogenesis. During each spawning
month, mature spermaries developed from a group of <125 μm spermaries. Virtually all spermaries >190 μm were released each
month, and most of the spermary volume in mature male polyps was generated anew each month of spawning. Among reproductive
colonies, polyp fecundity increased with colony height from 50 to 200 cm. Per capita fecundity of >200 cm tall female colonies
was lower than for 150 to 200 cm colonies, but whole colony fecundity of large colonies was greater due to the exponential
increase in the number of polyps that occurs with increasing colony height. In male colonies, both polyp and colony reproductive
output increased with colony height. The large amounts of sperm produced by large male colonies probably contributes to the
high rates of in situ fertilization observed in P. porosa. Differences in fecundity as a function of colony size and sex suggest differences in some combination of the cost of reproduction
and/or allocation of resources to reproduction.
Received: 9 September 1998 / Accepted: 7 June 1999 相似文献
10.
The wedge sole Dicologlossa cuneata (Moreau, 1881) is a coastal species that lives along the inner shelf waters of the Gulf of Cadiz down to a depth of 115 m.
Its fishery, the size composition of the exploited population, and its reproduction have been studied on the basis of data
acquired from commercial statistics from 1984 to 1994 and from sampling carried out during 1993 and 1994. The relative abundance
of the species and its geographic and bathymetric distribution have been examined by analysis of four trawl surveys carried
out from 1992 to 1994. D. cuneata is captured mainly by the trawl fleet, and to a lesser extent by gillnet gears. Wedge sole fishery has a marked seasonality.
Size-frequency distributions from commercial samples and from bottom-trawl surveys are very similar, ranging from 12 to 26 cm
total body length (TL). D. cuneata is a “repeat-spawner”. Peak spawning is from January to May. Females attain sexual maturity at 18 cm TL, while sexually mature
males have been observed at 15 cm TL. The flexibility of the spawning strategy of D. cuneata throughout its distribution range is discussed. The scarcity of small specimens in the monthly samples and sequential spawning
throughout the year prevented the estimation of growth parameters by means of length-frequency analysis. D. cuneata is present in greatest abundances in the sandy–muddy bottoms of the Guadalquivir River mouth at 15 to 30 m depth. Its optimum
habitat coincides with the principal commercial fishing grounds. The possibility of reproductive vertical migration is discussed,
but more precise data are needed before a viable hypothesis can be made.
Received: 1 July 1997 / Accepted: 27 November 1997 相似文献
11.
Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef 总被引:2,自引:0,他引:2
The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate
the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations.
S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore
reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from
December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies
in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of
multi-locus genotypes indicated a high number of unique genotypes (N
go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role
of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations
indicated that gene flow is restricted between some reefs (F
ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F
ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation.
Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern
in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene
flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further
from the coast.
Received: 10 July 2000 / Accepted: 5 October 2000 相似文献
12.
Life cycle of the copepod Calanus hyperboreus in the Greenland Sea 总被引:11,自引:0,他引:11
H.-J. Hirche 《Marine Biology》1997,128(4):607-618
The seasonal ontogenetic migration of the Arctic copepod Calanus hyperboreus was described from surface-to-bottom hauls in the central Greenland Sea Gyre (GSG) and in the Westspitsbergen Current (WSC).
All stages except females spent the winter below 500 m in the GSG and below 1000 m in the WSC. Seasonal ascent begins in April,
and descent in July. For the C.␣hyperboreus population an active downward transport of 8.1 g m−2 dry weight during 8 months of overwintering was estimated, similar to flux rates of particulate matter in sediment traps.
Seasonal distribution of biomass was determined from weight measurements of single stages. Annual means varied from 4.0 to
9.2 g m−2 in two different years in the GSG and were 1.1 in 1 year in the WSC. The life cycle in the Greenland Sea was reconstructed
from field data on stage composition, vertical distribution, reproduction, and moult cycle phase from tooth development of
CV. Laboratory experiments were conducted on the moulting of CIV and CV in fall. A 3-year (males) and 3- to 4-year (females)
life cycle is proposed for the GSG and 2 to 3 years for the WSC. However, the small number of young larvae and the incomplete
spring ascent by older copepodites observed in the WSC cast doubt on the reproductive success in the WSC. A suite of physiological
strategies and adaptations performed by the developmental stages support survival of this species in harsh environments.
Received: 25 January 1997 / Accepted: 11 February 1997 相似文献
13.
Sexuality and cyst formation of the spring-bloom dinoflagellate Scrippsiella hangoei in the coastal northern Baltic Sea 总被引:3,自引:0,他引:3
The temporal sequence and the magnitude of the sexual reproduction and subsequent cyst deposition of the common spring-bloom
dinoflagellate Scrippsiella hangoei (Schiller) Larsen was studied during spring 1996 on the SW coast of Finland, Baltic Sea. The abundances of the different
size of fractions of S. hangoei (14 to 18 μm, 18 to 22 μm and >22 μm) were monitored in the water column, and the deposition of resting cysts was measured
using moored sediment traps. Cyst sedimentation rates were measured throughout the seasonal cycle in order to estimate cyst
resuspension rates for the quantitative assessment of the fraction of population undergoing encystment. The onset of sexual
reproduction, indicated by a significant increase of the small cells (14 to 18 μm) representing gametes, occurred in a nutrient
replete environment well before the exponential growth phase and peak abundances of vegetative cells. Gamete formation was
followed by high abundances of large cells (>22 μm) representing planozygotes, and subsequent sedimentation of resting cysts.
Approximately 60% of the asexually growing bloom population was estimated to form planozygotes, suggesting that encystment
was an important factor in bloom termination and possibly plays a role in the regulation of the magnitude of the bloom. Finally
encystment accounted for 40% of the entire S. hangoei population, resulting in a considerable loss of the bloom population and an input of the vernal phytoplankton biomass to
the benthos.
Received: 11 December 1998 / Accepted: 8 April 1999 相似文献
14.
Reduced take-off ability in robins (Erithacus rubecula) due to migratory fuel load 总被引:11,自引:0,他引:11
Lind Johan Fransson Thord Jakobsson Sven Kullberg Cecillia 《Behavioral ecology and sociobiology》1999,46(1):65-70
Recent studies have shown that large fuel loads in small birds impair flying ability. This is the first study to show how
migratory fuel load affects flying ability, such as velocity and height gained at take-off in a predator escape situation,
in a medium-distance migrant, and whether they adjust their take-off according to predator attack angle. First-year robins
(Erithacus rubecula) were subjected to simulated attacks from a model merlin (Falco columbarius), and take-off velocity and angle were analysed. Robins with a wing load of 0.19 g cm−2 took off at a 39% lower angle than robins with a wing load of 0.13 g cm−2, while velocity remained unaffected. The robins did not adjust their angle of ascent in accordance with the predator's angle
of attack. Since many predators rely on surprise attacks, a difference in flight ability due to varying fuel loads found in
migrating robins can be important for birds' chances of survival when actually attacked.
Received: 28 October 1998 / Received in revised form: 12 January 1999 / Accepted: 30 January 1999 相似文献
15.
The benthic crustacean Saduria entomon occurs frequently in deeper parts of the Gulf of Gdańsk. It is one of a few species able to survive oxygen deficiencies in
its natural environment. The anaerobic heat production of S. entomon during 40 h of anoxia was determined. Additionally, the effects of size, sex and activity of the organism on its heat production
were investigated. Average heat production of S. entomon was 0.25 ± 0.16 mJ g−1 wet wt s−1 (n=55, avg. length 39 ± 6 mm). The amount of heat produced decreased with increasing body size. The heat production of S. entomon males was greater than that of females ( p<0.05). Specimens kept in chambers with glass beads and water were less active and had lower metabolic rates than those placed
in chambers containing water only (more active). During 40 h of anoxia S. entomon gradually decreased its heat production to 5–16% of aerobic level, demonstrating the high adaptation of this species to changeable
oxygen conditions in the Baltic Sea.
Received: 31 July 1997 / Accepted: 21 January 1998 相似文献
16.
The abundance, biomass and distribution of Solenicola setigera, a colonial heterotrophic protist found only with the centric chain-forming diatom Leptocylindusmediterraneus, are reported for four major ocean basins. The distribution is cosmopolitan, and abundances and biomass are usually low (<500 colonies l−1); however, in the summer of 1993, we observed a major biomass component (range = 5 to 31 μg C l−1) in the surface waters of the North Atlantic attributable to S. setigera. These colonies of S. setigera were exceptionally large, and unusual in possessing high abundances of Synechococcus sp., a normally solitary cyanobacterium, embedded in the matrix covering the cells. We hypothesize that this relationship
was mutually beneficial for both Solenicola setigera and Synechococcus sp.
Received: 5 January 1998 / Accepted: 22 May 1998 相似文献
17.
Although oysters are commercially very important in Brazil, there is still much dispute about the number of Crassostrea species occurring on the Brazilian coast. The dispute is centered around C. brasiliana, considered by some authors to be a junior synonym of C. rhizophorae. In this paper we compared, by allozyme electrophoresis, sympatric and allopatric populations of the two putative species.
Of the 17 loci analysed, five were diagnostic for the two species in sympatry (gene identity = 0.46 to 0.47), clearly demonstrating
that they are distinct biological species. Heterozygosity (h) levels were high for both species (h = 0.24 to 0.28), and no heterozygote deficiencies were observed in any population (local inbreeding, F
IS
= 0.141; P > 0.70). Levels of population structure in C. rhizophorae along 1300 km of coast were very low (population inbreeding, F
ST
= 0.026; P > 0.15), indicating that the planktonic, planktotrophic larvae of these species are capable of long-range dispersal.
Received: 14 January 1999 / Accepted: 8 December 1999 相似文献
18.
The taxonomic status of the Montastraea annularis species complex is unclear. Much evidence has been accumulated to support the separation into 3 species, but the presence
of intermediate morphotypes and the apparent lack of effective reproductive barriers in some areas are yet unexplained. Several
authors have made a call for the introduction of new traits that can be used to resolve differences among closely related
coral species. We collected skeletal and tissue samples from corals within the M. annularis species complex (15 each of M. annularis, M. faveolata, and M. franksi) and 10 morphological intermediates from several reefs in the Florida Keys. Multivariate analysis of corallite skeletal measurements
supported the separation of the species complex into three taxa. We detected two main fluorescence emission peaks at 480 nm
(turquoise) and 515 nm (green) that were not distributed equally among the three species. Every M. annularis colony had a major turquoise fluorescence peak. Some had a weak green secondary fluorescence peak. Colonies of M. faveolata and M. franksi had either the green or turquoise fluorescence peak, but at significantly different frequencies. The intermediate morphotypes
proved to be highly heterogeneous with respect to both micromorphology and fluorescence, and their nature could not be fully
explained. We were not able to separate the three species using fluorescence characters alone, however this new trait does
increase our understanding of the taxonomic structure within the M. annularis species complex.
Received: 21 January 2000 / Accepted: 1 September 2000 相似文献
19.
DNA sequence diversity of octopods was investigated using the mitochondrial cytochrome oxidase III gene (mtCOIII). DNA was
obtained from ethanol- or formalin-fixed tissue of 15 specimens belonging to Octopus mimus Gould, 1852, Octopus vulgaris Cuvier, 1797 and Scaeurgus unicirrhus d'Orbigny, 1840, from coastal waters of the Mediterranean (France), the southwestern Atlantic (Brazil), the Caribbean (Costa
Rica) and the southeastern/tropical Pacific (north Chile/Costa Rica). A 612 bp fragment of the mtCOIII gene was sequenced
and aligned to the orthologous sequences available from northeastern Pacific Octopus species. Possible phylogenetic relationships were reconstructed. The mtCOIII gene tree revealed two main clusters, one comprised
O. rubescens, O. dofleini and O. californicus, while the other included all O. vulgaris specimens, O. bimaculatus, O. bimaculoides and O. mimus. With one exception all South American haplotypes including O. bimaculatus and O. bimaculoides appeared as the sister group of the Mediterranean haplotype of O. vulgaris, indicating that most of the South American O. vulgaris specimens investigated would not belong to the recently redescribed species O. vulgaris restricted to the Mediterranean and eastern Atlantic. The treatment of O. mimus as a species distinct from Mediterranean O. vulgaris is supported by a high nucleotide divergence of 12.7%. Based on the mtCOIII gene tree the existence of cryptic species among
O. vulgaris-like octopods is suggested.
Received: 15 January 1999 / Accepted: 15 October 1999 相似文献
20.
The structure of the larval fish assemblages in three large estuarine systems on the KwaZulu-Natal coast of South Africa
was examined using a combination of univariate, distributional and multivariate techniques. The database was comprised of
a full annual set of larval fish samples taken from each estuarine system: Durban Harbour, Richards Bay Harbour and St Lucia
Estuary. The mean monthly densities of each species in each system were used in the species matrix, and the mean monthly values
of salinity, temperature and turbidity were used in the environmental matrix. The mean species diversity and evenness index
were significantly higher in Durban Harbour (H′ = 1.03, J′ = 0.65) than in the other two systems. The cumulative dominance curve showed that St Lucia Estuary has a high dominance
of a few species, with Richards Bay Harbour intermediate and Durban Harbour being the most diverse. Classification and MDS
(multiple-dimensional scaling) analyses of larval fish densities in all three systems grouped together into three main clusters
on the basis of system. The species similarity matrix (inverse analysis) clustered into five groups at the 25% similarity
level. The MDS analysis of the same matrix showed that the groups separated out according to the degree of estuarine association
of a species and hence habitat type. The species most responsible for system groupings were: Glossogobius callidus, Gilchristella aestuaria, Stolephorus holodon, Croilia mossambica and Gobiid 12. The “best fitting” of the environmental variables to explain the larval fish community patterns in each system
was turbidity on its own (weighted Spearman's rank correlation, ρw = 0.55). The relationship of larval densities to environmental conditions was shown to be species-specific with estuarine
species (e.g. G. callidus and G. aestuaria), having a strong positive correlation with temperature and turbidity but negative correlations with salinity. In summary,
much longer term studies with more sites within each system are needed to assess whether the larval fish assemblages are stable
or at an equilibrium (both spatially and temporally) and whether these assemblages are indicative of the relative “health”
and nursery function of the system.
Received: 28 April 1999 / Accepted: 30 May 2000 相似文献