The effect of prey size on growth of the carnivorous polychaete Halla okudai was evaluated in feeding experiments by combining three size classes of the prey, the clam Ruditapes philippinarum, with three size classes of the polychaete. Small polychaetes showed a significantly higher growth efficiency (growth increment / ingested portion of prey, measured as energy content) with small prey than with large ones. The reverse relation was observed in medium and large polychaetes. These results suggest that the optimal size of prey for this polychaete is 10 to 20% of its own body weight. The amount of jelly-like material secreted by the polychaete during handling increased with prey size; thus, handling was considered to be another large cost in the foraging behavior, in addition to the energy expended in searching.

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The intertidal biota of Hatakejima Island in Tanabe Bay, central Japan, was investigated in May, 1993. A survey of selected animal species around the entire coast of the island revealed different patterns of distribution in relation to wave exposure and substratum type. Comparison between the present data and those obtained in 1983 shows that several species obviously extended or contracted their distribution ranges around the island. In the survey of a selected area on the south coast, 173 macro-benthic species including 112 animal and 61 plant species were recorded. Mollusca and Crustacea were dominant among the animals, and Rhodophyta among the plants, in terms of number of species. Comparison between the present data and those obtained in 1969 and 1984 on the south coast reveals that the total number of animal species and their distribution ranges decreased from 1969 to 1984 and increased from 1984 to 1993. The species with a southern geographical distribution (<35°N) contracted and the indicator species of eutrophic water expanded their ranges from 1969 to 1984, and the reverse changes occurred from 1984 to 1993. Photographs show drastic changes in the shore scene: obvious sedimentation in 1984 and alternation of the dominant sessile bivalves between 1969 and 1993. The fluctuation in abundance of the species with a southern geographical distribution paralleled changes in the water temperature, and the fluctuation in abundance of the indicator species of eutrophic water paralleled changes in the indices of nutrient level. An influence of these environmental factors on the faunal changes of the intertidal Hatakejima Island during the last 25 years is inferred.

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Two species of tropical lancelet, Epigonichthys maldivensis (Cooper) and E. lucayanus (Andrews), were collected from bottom sand dredged by SCUBA-divers at depths of 10-14m among coral reefs in Nanwan Bay, southern Taiwan, in June, 1996. The average density, inclusive of both species, was roughly 25 ind. m^-2, with E. maldivensis in the minority. Many individuals of both species longer than 13mm were sexually mature. The present specimens represent the second record from Taiwan of the circum-tropical E. lucayanus after a gap of 20 years and the first find in Taiwan of the Indo-West Pacific E. maldivensis. SEM observations of the gut contents and material extracted from the sandy bottom of the habitat suggest that the lancelets may feed on surface detritus. Some morphological notes and a key to 5 East Asian lancelet species are also given.

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Two sympatric forms (I and II) of the estuarine grapsid crab Hemigrapsus penicillatus from the Nanakita River (Sendai, Japan) were detected by starch gel electrophoresis. Form I consists of individuals possessing the allele 6Pgd^B, while Form II has the allele 6Pgd^C. Heterozygote individuals (genotype of B/C ) were not observed at the 6Pgd locus. Form I is also characterized by the alleles Aat-2^C and Pgm^A, while Form II has the alleles Aat-2^B and Pgm^B. Morphological analysis revealed that the patch of soft hairs on the male chela in Form II individuals is much larger than that in Form I. The above results suggest that the two sympatric forms are reproductively isolated and represent sibling species.

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A simple coring device was designed for obtaining surface sediments and the overlying, near-sediment-surface water in lakes and shallow marine bays. It consists of a removable corer tube and valve attached to the inside wall of an Ekman grab by a clamp. The device has several advantages as follows: 1) core samples can be obtained with minimal disturbance to the sediment-water interface; 2) samples can be successfully collected even from sandy bottoms; 3) it can be easily operated even from a small boat.

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The distribution and abundance of benthic animals and their relationship with tidal height, large-scale (10-100cm) rock-surface topography, and small-scale (0.1-5cm) rock-surface topography were studied in the Intertidal community of an exposed rocky shore in northern Japan. Both scales of rock-surface topography strongly affected the distribution and abundance of most sessile and mobile species. Species-specific use-patterns were observed in both scales of rock-surface topography. Tidal height affected the largecale topographic use patterns of benthic animals, but not the small-scale topographic patterns. Chthamalus challengeri had a wider niche breadth and smaller niche overlap of rocksurface topography than the competitively superior species Septif er virgatus and Mytilus trossulus. This suggests that niche partition contributes to species coexistence in intertidal habitats where predation and disturbance rarely play an important role in reducing competition.

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