Influence of environmental disturbances and reproductive strategy on genetic diversity and differentiation of Zostera marina populations on the southern coast of Korea

The genetic diversity and differentiation of four Zostera marina populations along the southern coast of Korea were estimated using random amplified polymorphic DNA (RAPD) markers to determine the effects of natural and anthropogenic stresses and reproductive strategy on within‐population genetic diversity. The mean number of alleles and gene diversities, indicating population genetic diversity, was highest in the Z. marina population that was exposed to repeated environmental disturbances, and lowest in the most undisturbed population. The higher genetic diversity in the disturbed population was associated with a higher contribution of sexual reproduction to population persistence. This suggests that both the level of disturbances and the reproductive strategy for population persistence contributed significantly to population genetic diversity at the study sites. According to the analysis of molecular variance (AMOVA), 76% genetic variation was attributable to differences among individuals within populations. The observed genetic differentiation (F_ST = 0.241) among Z. marina populations at the study sites appeared to result from reduced meadow size, increased genetic drift, and a high incidence of asexual reproduction. Increased population genetic diversity can enhance resistance and resilience to environmental disturbances; thus, this investigation of seagrass population genetics provides valuable new insights for the conservation, management, and restoration of seagrass habitats.     

Factors involved in growth plasticity of cockles Cerastoderma edule (L.), identified by field survey and transplant experiments

In Arcachon Bay, a macrotidal coastal lagoon in southwest France, growth rates of cockles Cerastoderma edule (L.) differ greatly between locations. Sampling of populations at different tidal levels showed that the mean shell length was significantly and positively correlated with immersion time, whereas no correlation was found with population density and microphytobenthos biomass. Transplants of cockles between two intertidal sites were used to examine the relative importance of habitat and site of origin for growth rate and condition index. Artifacts due to manipulation were assessed, i.e. the impact of enclosures on growth, conditon index and mortality. During a 5-mo reciprocal transplant experiment, growth rates of the transplanted cockles and the cockles already present were similar, whereas the sites of origin did not affect growth rate. Condition index, however, displayed significant differences in relation to both transplant and origin sites. During a further 6-mo experiment in which cockles were transplanted from one site to four new sites, growth was mainly influenced by tidal level. These results indicate that net growth started when cockles were immersed 30% of the time. It is concluded that, on the scale of Arcachon Bay (156 km²), differences in growth and condition between cockle populations are largely phenotypic. Tidal level (i.e. food supply and emersion stress) accounts for most of these differences, but the existence of genetically or physiologically different populations cannot be excluded.     

Low calcification rates and calcium carbonate production in Porites panamensis at its northernmost geographic distribution

Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO₃ · cm^?2 · yr^?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr^?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO₃ · cm^?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO₃ · m^?2 · yr^?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.     

Evidence of Ostrea lurida Carpenter, 1864, population structure in Puget Sound,WA, USA

Species traits that carry adaptive advantages such as reproductive timing and stress resilience may differ among populations. Knowledge and consideration of these traits should, therefore, be integrated into conservation efforts that include long‐term persistence of species. To test for adaptive differences between Olympia oyster, Ostrea lurida, populations a reciprocal transplant experiment was carried out monitoring survival, growth and reproduction using three established populations of O. lurida within Puget Sound, WA, USA. Performance differed for each population. Ostrea lurida from Dabob Bay had the highest survival at all sites but the lowest reproductive activity and growth. Oysters from Oyster Bay demonstrated the greatest proportion of brooding females at a majority of sites with moderate growth and survival. Together these data suggest the existence of O. lurida population structure within Puget Sound and provide information on how broodstock should be selected for restoration purposes.     

Effect of pollution on genetic diversity in the bay mussel Mytilus galloprovincialis and the acorn barnacle Balanus glandula.

To test if environmental contamination acts as a selection force affecting genetic diversity at the population level, two intertidal invertebrate species, Mytilus galloprovincialis and Balanus glandula, were collected from seven different bay sites in southern California. Collections were made at three relatively pristine 'clean' sites and four 'impacted' sites exposed to heavy industrial or boating activity, and which had previously been identified as having measurable levels of pollution. Genetic diversity at each site was assessed by comparing fragment polymorphisms generated from genomic DNA by randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). All populations retained a large amount of genetic diversity and were genetically similar to each other. However, several different measures of diversity indicated that, for most primers, the populations of both species from impacted sites had lower genetic diversity compared to those populations from clean sites. Individuals at impacted sites were more likely to share the same haplotypes than were those from clean sites. Few bands seen in the clean sites were absent from the impacted sites or vice versa, but a number of bands in the clean site populations were significantly less common in the impacted populations, while a few bands uncommon in clean site populations were more common at impacted sites. Together, these results suggest that pollution at the impacted sites may reduce genetic diversity among the resident invertebrate populations.     

Genetic seascape of the threatened Caribbean elkhorn coral,Acropora palmata,on the Puerto Rico Shelf

It has been proposed that the elkhorn coral Acropora palmata is genetically separated into two distinct provinces in the Caribbean, an eastern and a western population admixing in Western Puerto Rico and around the Mona Passage. In this study, the genetic structure of A. palmata sampled at 11 Puerto Rican localities and localities from Curaçao, the Bahamas and Guadeloupe were examined. Analyses using five microsatellite markers showed that 75% of sampled colonies had unique genotypes, the rest being clone mates. Genetic diversity among genets was high (H_E = 0.761) and consistent across localities (0.685–0.844). F_ST ranged from ?0.011 to 0.047, supporting low but significant genetic differentiation between localities within the previously reported eastern and western genetic provinces. Plots of genetic per geographic distances and significant Mantel tests supported isolation‐by‐distance (IBD) within Puerto Rico. Analysis with the software STRUCTURE favored a scenario with weak differentiation between two populations, assigning Eastern Puerto Rican locations (Fajardo and Culebra), Guadeloupe and Curaçao to the Caribbean eastern population and Western Puerto Rican locations (west of Vega Baja and Ponce), Mona and the Bahamas to the Caribbean western population. Vieques and San Juan area harbored admixed profiles. Standardized F_ST per 1000 km unit further supported higher differentiation between localities belonging to different STRUCTURE populations, with IBD being stronger within Puerto Rico than on larger regional scales. This stronger genetic transition seems to separate localities between putative eastern and western provinces in the Eastern Puerto Rican region, but not around the Mona Passage.     

Current status of coral takeover by an encrusting excavating sponge in a Caribbean reef

On Caribbean reefs, the excavating sponge Cliona tenuis opportunistically colonized dead skeletons of the elkhorn coral Acropora palmata after its massive die‐off in the 1980s. Further C. tenuis population increase occurred by colonization of other coral species, causing coral tissue death through undermining of live tissue and lateral growth. To follow up on a previous (2001) characterization of the abundance and size structure of C. tenuis at Islas del Rosario (Colombia), these factors were again estimated in 2014, along with its substratum utilization. The fate of sponge individuals colonizing massive coral colonies marked in 2001–2004 was also followed. By 2014 C. tenuis was still disproportionally occupying dead A. palmata branches, but its abundance and density, and the cover of other benthic elements, had not significantly changed over the 13‐year period, suggesting that a stasis has been reached. Cliona tenuis was thus initially favored in the 1980s, but substratum monopolization did not occur. From 2001 to 2014, small individuals increased in number and very large ones decreased, suggesting not only that new recruitment is occurring, but also that larger sponges are shrinking or fragmenting. Marked sponges continued killing corals over the first few years, but over longer times they retreated or died, allowing corals to resume upward growth. However, it could not be ascertained whether the sponge retreat was age‐related or the result of some environmental effect. The apparent preference for recently dead clean coral by larvae of C. tenuis and its current dynamics of recruitment, growth, fragmentation and mortality have stabilized its space occupation at Islas del Rosario.     

Field assessment of biochemical stress indices for the sandworm Neanthes virens (Sars)

Certain biochemical stress responses have been observed in the laboratory for Neathhes virens subjected to various environmental and pollutant stressors. The purpose of the present study was to determine whether similar alterations in these biochemical parameters could be detected in a natural population of N. virens from a contaminated site as compared with animals from a nearby reference site. A site in Portland Harbor, Maine, adjacent to an oil storage facility with oil-contaminated sediments was selected as the experimental study area and the reference site was at Pine Point, approximately 15 miles south of Portland.Animals were collected from the two sites on consecutive days on a bimonthly basis at low tide within a day of the full moon from September 1981 through March 1982. Coelomic fluid samples were taken within 2 h after collection and the animals were then frozen in liquid nitrogen for transport back to the laboratory. Coelomic fluid samples were analyzed for glucose and the frozen tissues were analyzed for glycogen, lipid and free amino acid concentrations.Significant differences in these parameters were often observed between the two populations. The glycogen content of animals from the contaminated site was always less than that of animals from the reference site, whereas the lipid levels were always higher. Significant differences between the free amino acid composition of the animals from the two sites were also observed. Although distinct biochemical differences can be detected between these two populations, the considerable biological variation in these parameters may limit their usefulness for field monitoring investigations for this species.     

Vertical zonation and aggregated distribution of the Manila clam on subtidal sand flats in a coastal brackish lagoon along the Sea of Japan

The Manila clam, Ruditapes philippinarum, has maintained small‐sized populations in a semi‐enclosed brackish lake along the Sea of Japan, the Honjo area of Lake Nakaumi, although the environment and biota of this area have changed dramatically due to a large‐scale reclamation project. There should be underlying processes that enable the restoration of this species from small‐sized populations, such as the existence of source (i.e. reproductive) populations in other areas and depth zones of the lake. However, there has been no robust, properly designed evaluation of the distribution of the Manila clam in the subtidal sand flats. In order to elucidate the possible mechanisms that allow for the persistence of populations of the Manila clam, we examined the spatiotemporal and vertical variation in distributions of 0‐age clams in the subtidal zone of sand flats. Seasonal effects on population variations showed erratic changes among depth zones without a decreasing trend along the depth gradient. Further, many local populations became extinct even in the shallower zones due to seasonal (summer) hypoxia at deeper zones and hypoxia by the accumulation of key benthic species (Asian mussel and decaying macroalgae) in mats at shallower zones. A few surviving local populations were stable with a spatial‐fragmental (patchy) distribution, associated with fragmented accumulations of Asian mussels and macroalgae. Efforts to maintain stable populations and to restore this species in the subtidal area may depend on these small, restricted, patchy local populations. These findings suggest that high fertility and productivity of the Manila clam as well as patchy distribution of small populations may contribute to the maintenance of the population and the avoidance of extinction (by spatially diffusing the risk of extinction) in harsh environments resulting from the reclamation project.     

Elevation of cytochrome P450-immunopositive protein and DNA damage in mussels (Mytilus edulis) transplanted to a contaminated site

Mytilus edulis were collected from a reference site (Port Quin) and an urban/industrial contaminated site (New Brighton) in the UK during June 1999. Levels of PCBs (sigma7 congeners) and CB-138 were determined to be, respectively, 21 fold and 16 fold higher in the mussel digestive glands from New Brighton. Levels of CYPIA-immunopositive protein were 1.5 fold higher (P < 0.05) at the polluted site but the levels of DNA strand breaks were 1.3 fold higher (P<0.05) at the reference site. Mussels from Port Quin were placed in cages at both sites and both transplanted and indigenous populations sampled in September (13 weeks). Mussels transplanted from the reference site to the industrial site, reported elevated levels of CYP1A-immunopositive protein (1.4 fold; P < 0.05) and higher levels of DNA damage (1.2 fold; P < 0.05) compared to caged populations at the reference site and a PCB loading similar to the populations from the polluted site. Moreover, transplanted mussels had DNA damage 1.8 fold greater (P < 0.05) than indigenous mussels at the transplant site. These changes were small but significant when compared to the observed temporal changes in the indigenous populations.     

A comparison of growth patterns between non‐indigenous Halophila nipponica and the native sympatric Zostera marina on the southern coast of the Korean peninsula

The growth dynamics of two co‐occurring seagrass species, Zostera marina and Halophila nipponica, were examined on the southern coast of the Korean peninsula. Zostera marina is a native dominant seagrass species in Korean coastal waters, whereas H. nipponica is a non‐native tropical and subtropical species that has extended its distributional range to the temperate coastal areas of Korea. To examine the differences in the growth dynamics of H. nipponica and Z.  marina, their morphology, density, productivity and biomass, as well as local environmental conditions, were monitored monthly from January 2008 to July 2009. Underwater irradiance at the study site was the highest in April 2009 and the lowest in January 2008. Water temperature ranged from 10.4°C in January 2009 to 24.8°C in September 2008. Significant differences in growth dynamics were observed between the species, due to the effect of water temperature at the study site. Density and areal productivity were the highest in April 2008 and June 2008, respectively, for Z.  marina but the highest in July 2008 for H. nipponica. Leaf size, shoot height and shoot weight were the highest in July 2008 for Z.  marina but the highest in August 2008 or September 2008 for H. nipponica. The productivity of both species was strongly correlated with water temperature at the study site. However, the productivity of these species was not strongly correlated with underwater irradiance or the nutrient availability of either the water column or sediment pore water. Zostera marina exhibited the ecological characteristics of a temperate seagrass, whereas H. nipponica retained the features of a subtropical/tropical seagrass, even after adapting to the temperate coastal waters of Korea.     

Regional and species specific sexual reproductive patterns of three zooxanthellate scleractinian corals across the Eastern Tropical Pacific

Sexual reproduction of zooxanthellate scleractinian corals in the Eastern Tropical Pacific (ETP) is influenced by the interactive effects of regional and local oceanographic conditions, as well as a variety of other environmental factors. Differences in spatial and temporal gamete development and reproductive patterns of three widespread scleractinian corals of this region—Pocillopora damicornis (branching colony morphology, characterized as hermaphrodite broadcaster), Pavona gigantea (massive colonies, characterized as gonochoric broadcaster/sequential co‐sexually hermaphroditic) and Porites panamensis (encrusting colonies, characterized as gonochoric brooder)—were evaluated at local and regional scales across the ETP. This area extended from the Gulf of California (24°N) to the southern coast of Ecuador (–1°S), including offshore islands, using existing data pooled from prior studies. Predictive models were employed based on environmental variables: sea surface temperature, daylight hours, diffuse attenuation co‐efficient at 490 nm and photosynthetically active radiation. Datasets were extracted from satellite images ( https://oceancolor.gsfc.nasa.gov ) and analysed using WAM_STATIST ver. 6.33® software to obtain monthly average data from each site. The spatial (region, sub‐region and site) and seasonal (wet, dry) variation in reproductive activity (% colonies with gametes) differed among the three species; significant interactions were season × sub‐region for P. damicornis, season × site (sub‐region) for P. gigantea, and season × site for P. panamensis, for which sub‐region was not considered as a factor. The predictive models also suggest that gamete production/maturation of P. damicornis and P. gigantea is influenced by local differences in sea surface temperature and daylight hours. Porites panamensis was not correlated with any environmental variable examined. Variations in local and regional reproductive developmental patterns are likely an acclimatization response by each species imposed by the timing and duration of local stressor events. This analysis has provided insights into the diverse local and regional physical drivers that affect species responses and acclimatization in sexual reproduction across the ETP.     

Acropora coral colonies as microhabitats for sponges in Tayrona National Natural Park,Colombian Caribbean

Sponges are sessile organisms capable of colonizing diverse substrata. In the Caribbean, coral reefs have suffered a drastic decline, and branching corals of the genus Acropora have been widely decimated. On dead coral skeletons and around surviving tissue the settling of sessile organisms can be observed, sponges being common. In order to investigate whether or not sponges have a preference for a particular species of coral, or for specific microhabitats of the colonies, we evaluated species composition, cover, richness and diversity of sponges colonizing the dead parts of still live colonies of the branching corals Acropora palmata and Acropora cervicornis in five locations of the Tayrona National Natural Park in the Colombian Caribbean. Ten colonies of Ac. palmata were quantified in each of the five locations, and eight Ac. cervicornis colonies in each of two locations. Quantification was carried out using video taken within 0.625‐m² photoquadrats. Seventeen sponge species were found, 13 of them associated with Ac. palmata and seven with Ac. cervicornis. Desmapsamma anchorata, Clathria venosa and Scopalina rutzleri were found to be common to all Ac. palmata locations, while De. anchorata occurred in the two Ac. cervicornis locations. On Ac. palmata, encrusting sponges dominated, while on Ac. cervicornis branched and lobed sponges predominated. Significant differences in sponge cover were not found among locations but were observed in the sponge species present. On Ac. palmata the species with highest cover were D. anchorata and Cla. venosa, while on Ac. cervicornis it was De. anchorata. The richness and diversity of sponges were low for both coral species, and their varying distribution can be attributed to the differences in available substrate for attachment, given coral colony morphology; for Ac. palmata, sponges predominated on the underside of the branches, semi‐cryptic areas and colony bases, whereas for Ac. cervicornis, they were located over the entire area of the cylindrical branches. Surviving colonies of Ac. palmata and Ac. cervicornis that are still erect offer additional microhabitats for reef sponges, some of which can be found directly interacting with live coral tissue, further threatening their recovery.     

Bioaccumulation and depuration of Zn and Cd in mangrove oysters (Crassostrea rhizophorae, Guilding, 1828) transplanted to and from a contaminated tropical coastal lagoon

In order to study Zn and Cd accumulation and depuration, a set of oysters, Crassostrea rhizophorae, were transplanted to a metal contaminated coastal lagoon and another one was harvested there and transplanted to a non-polluted site. C. rhizophorae oysters and Perna perna mussels native from both sites were collected in order to monitor variability of metal concentration in resident populations. After three months exposure, oysters transplanted to the polluted site accumulated fourfold Zn (307-1319 microgg(-1)) without reaching the concentration level of resident oysters (9770 microgg(-1)). Cadmium concentrations had a slight but significant decrease during the same period (1.25-0.54 microgg(-1)). Oysters transplanted to the non-polluted site, showed threefold Zn depuration (6727-2404 microgg(-1)), while Cd had no significant variation (0.90-1.45 microgg(-1)). Results showed that transplanted oysters do not reach heavy metal concentrations in indigenous populations suggesting transplanted organisms would be better used to evaluate bioavailability instead of environmental concentrations.     

Biology of evechinus chloroticus (Echinoidia: Echinometridae) from different localities

Growth bands were demonstrated in the apical plates of Evechinus chloroticus by grinding horizontal sections which were air dried for several days and treated with lactophenol + 0.5% ferrous ions for a few minutes. Only one dark band was formed each year, during summer.

Evechinus grew considerably faster at Kaikoura than at Kaiteriteri, about 2 cm and 1 cm a year respectively, until growth slowed with increasing age. These differences may relate to food availability.

Numbers in year classes varied considerably, and in some Evechinus populations year classes were absent. Most urchins at Kaiteriteri were less than 6 + years old, but urchins up to 10 years old were aged at Kaikoura. More old urchins were found in deeper populations at Kaikoura, where a number may have been up to 15 years old.

Size‐frequency distributions varied markedly among populations. Distributions appear most influenced by recruitment intensity, and higher growth rates and greater longevity were found in populations with predominantly large urchins, as at Kaikoura.     

Population genetic diversity and structure of a dominant tropical seagrass,Cymodocea rotundata,in the Western Pacific region

Cymodocea rotundata is an ecologically important tropical pioneer seagrass species distributed in the Indo‐Pacific region. The population genetic diversity and structure of this species were analysed at 46 sites spanning the Philippines, Ryukyu Islands (northern limit) and Hainan Island, by using microsatellite simple sequence repeat (SSR) markers. Analyses revealed the persistence of C. rotundata likely relies on local population dynamics and fitness influenced by environmental gradients, with sexual reproduction prevalent in the Philippines while the Ryukyu and Hainan populations were predominantly established by clonal spread. Analysis of molecular variance showed significant genetic differentiation (P < 0.001) among three geographic regions: the Philippines, Ryukyu and Hainan. Furthermore, the mean fixation index value was very high (F_ST = 0.36), indicating poor dispersal potential or limited gene flow. Allelic richness and heterozygosity of C. rotundata was comparable in the Philippines and Ryukyu Islands populations. More private alleles were found in the Philippines and excess heterozygotes in the Ryukyu Islands. STRUCTURE analysis revealed that the Ryukyu and Hainan populations were mosaics of admixed alleles of individuals from the Philippines. An assignment test suggested that recruitment occurs from the Northeast Philippines to Ryukyu Islands. These results suggest that the Philippine populations are tropical seagrass hotspots and perhaps the origin of the populations in the Ryukyu and Hainan Islands. This scenario is most likely driven by the Kuroshio Current and island integration events during plate tectonic activities. The Philippine Archipelago is considered of high importance for conservation objectives and management plan of seagrasses. Likewise, the Ryukyu Islands are also important in terms of conserving regional diversity because locally adapted genotypes have important evolutionary potential in the face of environmental change.     

Variability in low tide populations of tuatua,Paphies donacina,in Pegasus Bay,Canterbury, New Zealand

Paphies donacina (Spengler, 1793) populations were surveyed at 11 low tide sites on surf beaches along Pegasus Bay, Canterbury, New Zealand, during summer 1998. Random sampling was not feasible. At the non‐random sites chosen the average number of tuatua per 5 m of shoreline ranged between 0.1 and 62. Total wet weight biomass m^‐2 was highest at the southern sites in the Bay. There were site‐related differences in length frequency distributions of tuatua populations. Northern populations included a wide length range and southern populations were dominated by larger bivalves. Average shell length increased significantly with distance south, being close to 40 mm at Waikuku and 80 mm at Taylors Mistake. The shell length: width and weight relationships were similar for tuatua collected over the whole geographic range. Average dry weight condition index varied significantly between sites (ANOVA F= 23.3, d.f. = 10, 329) depending on the length distribution of the contributing population. Where populations included a wide length range the condition index was positively correlated with shell length but in populations dominated by larger bivalves there was either no relationship or a negative relationship with shell length. Juvenile tuatua were found at average densities between 81 and 1200 m^‐2 at all sites except Taylors Mistake. The mean length of recruits ranged from 2.2 to 3.1 mm and shell length was independent of both juvenile and adult density. These results are discussed in relation to the environmental and other factors thought to influence population structure and recruitment of tuatua in Pegasus Bay.     

Influence of reach geomorphology on hyporheic communities in a gravel‐bed stream

The surface sediment, subsurface sediment, and hyporheos were sampled by freeze‐coring at three sites of contrasting geomorphology in a New Zealand gravel‐bed stream. No differences in size class composition were detected among the subsurface sediments of the three sites but the forced pool‐riffle (a stretch of stream where the sequence of pool and riffles is controlled by in‐channel bedrock outcrops) had significantly finer surface sediments than the other sites. The hyporheos of all sites was dominated numerically by insects, including nymphs of Deleatidium and Oniscigaster, and chironomid larvae. Of the non‐insect taxa, Isopoda, Oligochaeta, and Acari were most common. No significant differences existed between total invertebrate density or taxon richness at the sites. Aoteapsyche was found only in the plane bed site, whereas Nesameletus was found only in the forced pool‐riffle. Psilochorema and Nematoda occurred at significantly lower densities in the forced pool‐riffle than in the plane bed or floodplain sites. For most taxa, local variation within a site was greater than that between sites. Total invertebrate density was highest near the sediment surface but no significant differences were found between the three sites in this or any other depth layer. Significant site‐depth interactions were obtained for three taxa (Zelandobius, Ostracoda, and Oligochaeta) indicating that local geomorphology may result in differential depth distributions of hyporheic species.     

To what extent are the fish compositions at nearshore sites along a heterogeneous coast related to habitat type?

This study has tested the following main hypotheses. (1) The composition of fish assemblages in nearshore waters along the lower west coast of Australia will differ significantly among four habitat types (1–4), which could be distinguished quantitatively from each other by differences in the values for a statistically selected suite of enduring environmental variables. (2) The extents of the differences in ichthyofaunal composition among the four habitat types will statistically match those in the suite of environmental variables that distinguish those habitat types. A 60.5 m long seine net, with 9 mm mesh in the bunt, was used seasonally for 2 years to sample fish from sites representing each of the four nearshore habitat types, which differed broadly in their exposure to wave activity and the extent and location of seagrass beds. The compositions of the fish faunas in each habitat type were significantly different from each other in all but one case. Ichthyofaunal composition did not differ significantly between years in any habitat type and differed significantly among seasons in only one habitat type. The arrangement of the rank orders of similarity in matrices constructed from the abundances of the fish species at each site also did not differ between years but did differ among seasons. Moreover, the arrangement of the ranks in the similarity matrices produced from the ichthyofaunal data recorded at the various sites in each season were significantly correlated with that in the distance matrix constructed from the environmental data for those sites, with the correlation (ρ) ranging from 0.476 in winter to 0.696 in autumn. These results thus demonstrate that the extents of the differences in the fish compositions among the various habitat types parallel those in the environmental data for the corresponding habitat types. The subset of species that provided the best correlation with the environmental distance matrix, and which was thus most responsible for distinguishing among the fish compositions at the four habitat types, was also determined for each season.     

Inter‐population differences in feeding ecology under nitrogen‐limited diets: Field growth and the role of cannibalism in limiting/improving reserve accumulation

Growth is determined by an organism's physiology, physical environment, and biological conditions, including food availability and any intra‐ and inter‐specific interactions that can affect feeding activity. To analyse how all these factors interact to produce final growth in the herbivorous/detritivorous crab Neohelice granulata, we performed field and laboratory experiments with juveniles and adults from three populations which differed genetically as well as in their physical environment and the organic matter (OM) content in the soil that serves as food. We evaluated (a) growth in the field: Juveniles of the three populations were cross‐transplanted in exclusion cages; (b) effect of the presence of adults on juvenile feeding: We measured the feeding activity of small juveniles in presence/absence of an adult male as potential predator in the field; and (c) effect of diet on cannibalism: We analysed the cannibalistic behavior of adult males from two of the populations in the laboratory after they had received protein‐rich (24%) and protein‐poor (3%) diets. In experiment (a), final size was similar for the crabs from all three origins but growth differed between sites. Experiment (b) showed that the presence of adults interfered with feeding activity at the two sites with lower weight indicators. In experiment (c), we observed that low protein diet increased the cannibalistic behavior of adult males, and this effect was more intense in crabs from the poorest food site. Our results contribute to understanding the set of factors and interactions involved in the response of individuals to the prevailing conditions in natural environments in order to maintain a growth rate, perhaps at the expense of different reserve accumulation. They also enable discussion of the limitations of approaches used in laboratory experiments.