Abstract: Growth patterns in the shell and soft parts of the dogwhelk Nucella freycineti were examined. Growth rings in the shells were investigated by X-ray photography and were shown to form annually. In snails that hatched in summer, the first rings formed in the first winter. The shell growth equation was determined based on the age character, population age structure, seasonal growth rate and size frequency distribution of the population. The maximum shell growth occurred in summer. The life span was estimated to be>11 years. Low physiological activity and/or starvation induced by low temperature might be main factor(s) causing the formation of annual rings, although age might also influence ring formation. Total body weight increased in late summer in males and from late summer to winter in females. Gonad weight showed a similar trend in each sex. After the reproductive season, shell growth occurred in summer, and body weight increased from summer to winter. These growth characteristics might promote higher survival and fitness.

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Abstract: We studied the community structure of mobile epifauna on the seagrass Enhalus acoroides at a subtidal seagrass bed in Thailand to examine whether the abundance and community structure of the epifauna are affected by (1) the position within the seagrass patches, and (2) the seagrass patch sizes. We collected mobile epiphytic animals on E. acoroides at the center and the periphery of large (>3.6m² in area) patches, and from small (<1.1m²) patches. The most dominant animal was a grass shrimp, Latreutes sp., followed by several species of gammarid amphipods, a polychaete and gastropods. Species richness, the total number of individuals and the number of the eight major species did not differ significantly between the center and periphery of the large patches. The density of Latreutes sp. was significantly smaller in the large patches than the small patches. Turbellaria spp. were also less common in the large pathces. In contrast, the density of a chaetognath (Spadellidae sp.) tended to be higher in the large patches. Species richness, total animal density, and the densities of other dominant animals did not differ significantly between large and small patches. These findings demonstrate that the position within E. acoroides patches has only a minor effect on the abundance and diversity of the epifaunal community, whereas the size of patches has a larger effect on the epifauna. It was also suggested that the response of mobile epiphytic animals to seagrass patch structure is scale-and species-specific.

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Abstract: The sulfur isotope composition of soft tissues of Bathymodiolus septemdierum, B.aduloides, B.platifrons, and B.japonicus collected from deep-sea hydrothermal vent and cold seep communities in Japanese waters was measured. The.δ34S values(-0.4 to+5.5‰ relative to CDT)of B.septemdierum were similar to those of hydrogen sulfide in the associated hydrothermal fluids(δ34S=+3.1 to+5.6‰). The fairly low δ34S values of B.aduloides(-15.4 to-12.4‰)indicate assimilation of hydrogen sulfide derived from the dissimilatory reduction of seawater sulfate by sulfate-reducing bacteria. On the contrary, B.platifrons and B.japonicus had much higher values(δ34S=+12.7 to+19.8‰), which fall within the common isotopic range of marine plankton, algae, and benthic animals.These two species appears to assimilate seawater sulfate(δ34S= +21‰)with limited kinetic fractionation of sulfur isotopes(up to-6‰).The present sulfur isotopic analysis provides evidence for two kinds of sulfur source, i.e., isotopically light hydrogen sulfide vs. heavy seawater sulfates. The previously documented. δ34S values of Bathymodiolus from the Mid-Okinawa Trough, which were different from those obtained in the present analysis, are evaluated in terms of the species'physiological ecology on the basis of available data.

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Abstract: A shallow Sargassum zone at around 1 to 2m depth was followed sequentially by an Eisenia zone at 2-7m depth, a Dilophus zone less than 1m wide, and a crustose coralline algal zone furthest offshore. Cobblestone areas were found here and there at 2 to 3m depth. Samples handpicked and/or obtained by air-lifting were obtained around a station in each zone and a cobblestone area in June, August, October, and December, 1990, and March, 1991. A matrix of Pearson's correlation coefficients of species composition with respect to the analytical unit of “site×time” was scaled multidimensionally. Behavioral areas of the MDS plots were similar between the Sargassum zone and cobblestone area, and between the Dilophus and crustose coralline algal zones, but the Eisenia zone was quite separate from these. A dendrogram of species-specific distribution pattern with respect to the analytical unit of. “species×time” showed three strata differing in linkage levels, i. e. 18 subclusters with linkage levels of extremely low dissimilarity, nine clusters of low dissimilarity linkage, and three superclusters linked at relatively high levels of dissimilarity. Out of the nine clusters, Clusters 1, 3, 5, 6, and 8 were characterized by having their highest relative densities in the crustose coralline algal zone, the Dilophus zone, the Eisenia zone, the Sargassum zone, and the cobblestone area, respectively. The respective superclusters were characterized by high relative densities in the following areas: Supercluster 1, either the Dilophus zone or the crustose coralline algal zone; Supercluster 2, the Eisenia zone; Supercluster 3, either the Sargassum zone or the cobblestone area. Subclusters corresponded to subtle variations of cluster characteristics. These facts demonstrate the important role of algae in the structure of benthic animal distribution.

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Abstract: Sexual and asexual reproduction of the fissiparous asteroid Coscinasterias acutispina(Stimpson)was studied in two populations(Kurosaki and Uozu)in Toyama Bay, Sea of Japan, during April 1998-March 1999(Kurosaki)and April 1998-October 1999(Uozu). A total of 96% and 87% of all starfish collected at Kurosaki and Uozu, respectively, showed signs of asexual reproduction by fission. Monthly changes in the ratio of regenerated arm length to maximum arm length revealed that starfish in these populations split most frequently in summer. There was a marked difference in the development of gonads between the two populations. In the Kurosaki population, monthly changes of gonad indices and histological observations on gonads indicated a distinct annual cycle, with a winter spawning season in both males and females. In the Uozu population, gonad indices remained low, and no starfish with mature gonads were observed during the study. An unbalanced sex ratio was observed in both populations; the Uozu population was composed entirely of males. The absence of mature gonads and the extremely biased sex ratio suggest that larval recruitment was low or absent in the Uozu population.

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