SEKIGUCHI, HIDEO (Faculty of Bioresources, Mie University). 1988. Taxonomical and ecological problems associated with phyllosoma larvae. Benthos Research (Bull. Jap. Assoc. Benthology), 33/34, 1-16. Several taxonomical and ecological problems, associated with phyllosoma larvae of the scyllarid and palinurid lobsters, are discussed as follows: (1) discrepancy between classification of phyllosoma larvae and their adults, based mainly on SEKIGUCHI (1986a), SEKIGUCHI snd SAISHO (1988) and unpublished data, (2) geographical distribution of the Panulirus japonicus group, based on SEKIGUCHI (1988), (3) relative abundance of the Panulirus species in Japanese and adjacent waters, based on SEKIGUCHI (1988), (4) phyllosoma larvae in Japanese waters, based on Wada et al. (1985), SAISHIO et al. (1983) and SEKIGUCHI (1986b, c), (5) why P. japonicus does not inhabit in Bonin (Ogasawara) waters and Japan Sea, based on SEKIGUCHI (1988), (6) mistery of the early life history of Panulirus japonicuslarval recruitment processes of the species, based on SEKIGUCHI (1985, 1986c).

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IMABAYASHI, HIROMICHI and TERUYOSHI IWATANI (Faculty of Applied Biological Science, Hiroshima University), 1988, Growth and distribution in planktonic larvae of the small bivalve Theora lubrica (Preliminary report). Benthos Research (Bull. Jap. Assoc. Benthology). 33/34, 17-24 Planktonic larvae of the samll semelid bivalve Theora lubyica, which developed from demersal eggs of approximately 60μm diameter, were reared at a water temperature of 12-25°C. The larvae grew linearly and the rate of growth increased with water temperature; 2.3μm/day at 12°C, 5.8μm/ day at 15°C and 7.8-12.5μm/day at 20°C. The size of first settled bivalve varied largely in shell length from 187.5 to 245.0μm (mean: 214.6μm). At a shallow waters where benthic bivalves were predominantly inhabited but disappeared almost in late summer (IMABAYASHI & TSUKUDA 1984), planktonic larvae after umbonal stage (shell length: 125μm) were collected more than 100 shell/m³ during a year and showed a maximum density of 7, 344 shell/m³ in spring. The diurnal investigation showed that the larvae were always concentrated near soft-muddy sediment and formed a small aggregation which migrated horizontally according to tidal current (maximum velocity: 19 cm/sec). Hence it is due mainly to the migration of aggregated larvae that the large settlemet occurs at suitable nursery ground.

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TAMAI, KYOICHI (Nansei Regional Fisheries Research Laboratory, Kochi). 1988. Distribution and life history of Prionospio ehlersi FAUVEL, 1928 (Polychaeta: Spionidae) in Japan. Benthos Research (Bull. Jap. Assoc. Benthology), 33/34; 25-32. Prionospio ehlersi was a common spionid polychaete in benthic communities of soft bottom sediments ifl western Japan. It favoured the muddy or sandy mud sediment in oxidized environments, whereas it scarcely occurred at the areas with reduced conditions (D.O. saturation percentage of the bottom water was less than 50%). The population generally had a biased sex ratio to female (1:2), and the worms did not mature until they had grown into the body size with 0.38mm in the width of peristomium or 4.4mg in wet weight. This polychaete was annual species, and had a extended breeding season as a population. For example, in Tosa Bay, mature individuals with eggs or sperm were observed from April to November, and newly recruited individuals were collected from August to December. The egg size ranged from 95 to 105μm in diameter.

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MATSUMASA, MASATOSHI and YASUSHI KURIHARA (Biological Institute, Faculty of Science, Tohoku University). 1988. Distribution patterns of benthic small crustaceans and the environmental factors in a brackish shallow-water lagoon, Gamo lagoon. Benthos Research (Bull. Jap. Assoc. Benthology) 33/34, 33-41. Distribution patterns of benthic small crustaceans and the environmental factors influencing them were investigated in a brackish shallow-water, Gamo lagoon. Four amphipods (Grandidierella japonica, Kamaka, sp., Corophium uenoi and Melita sp.) and a tanaid (Tanais stanfordi) were recorded. In the benthic sandy habitat, distributions of four amphipods overlapped greatly, and especially G. japonica and Kamaka sp. were abundant. Both species distributed on the subtidal area in winter and spring, but G. japonica dominantly appeared on the subtidal and lower intertidal area (below M.L.W.) and Kamaka sp. mainly appeared on the intertidal area above M. L .W. in summer and autumn. C. uenoi and T. stanfordi were abundant on the surface of a concrete embankment of the channel part. The seasonal change in number of C. uenoi corresponded to biomass of the filamentous algae Polysiphonia sp. growing on the embankment, but the seasonal change in number of T. stanfordi did not. A lot of tubes of C. uenoi were observed among filaments of Polysiphonia sp. and tubes of T. stanfordi in thin layer of sediment on the embankment. These indicate that those four benthic small crustaceans distribute correlating with substrata such as the bottom sediment, the thin sediment on embankment and the filamentous algae Polysiphonia sp. in Gamo lagoon.

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IMAI, TOSHITAME (Kanagawa Pref. Fish. Exp. Stn.), MICHIMASA CHIKAYAMA (Dept. Fish. Kanagawa Pref.), SAICHI KANASUGI (Kanagawa Pref. Fish. Exp. Stn.), KAZUNARI OGAWA, RYUICHI MITOMI and AKIHIKO MAKI (Chiyoda Dames & Moore Co. Ltd.). 1988. The structure of rock components of artificial reef and the spatial disbribution of abalones. Benthos Research (Bull. Jap. Assoc. Benthology), 33/34; 43-51. An underwater investigation was made by SCUBA diving at Matsuwa, Miura Peninsula, Kanagawa Prefecture, in order to clarify the favorable habitat structure for abalones on the artificial reef. The reef was constructed by a pile of rocks encircled by a concrete frame, considerable number of three abalone species, Haliotis sieboldii, H. gigantea and H, discus had been introduced previously. Firstly, all abalones attached on rocks of the reef were fished, and topographic features of the whole reef were surveyed. Then, all rocks were heaved up on board the boat for measuring their shape and size. All abalones caught with the location data, and identified to the species. The data were analyzed using computer graphics, on the raletionships between the structure of rock components and the spatial distribution of each abalone species. The reuslts were summarized as follows: (1) most of abalones were found close to the bottom less than 25cm in height, (2) most of abalones attached on shaded faces of piled rocks, (3) concerning the habitat preference by species, Haliotis discus outnumbered on the effectively sheltered faces of rocks not accessible by divers. This habit makes the species most difficult to retrieve in fishing among three abalone species. (4) Light condition was very important for abalone distribution. As for favorable condition of resting site, effectively sheltered and appropriately shaded condition seems to be more important than the shape and capacity of the room created by rock components.

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Phytal meiobenthos on eelgrass leaves was investigated in Amakusa, west Kyushu. Seasonal variation of nematode community was studied, especially on species composition, total nematode density and feeding type composition. The top rank taxon in the phytal meiobenthos was Harpacticoids and nematodes came the second throughout the year, while in April nematode became the top rank by sudden increase of a few dominant species. Total nematode density reached annual maximum in April, then decreased to low density in June, again increased and made small second peak in August. This seasonal fluctuation pattern is much similar with that of epiphyte biomass. The increase of epiphyte biomass seemed to contribute nematode abundance through increase of habitat complexity in micro-scale and food resource. In the feeding type analysis by WIESER'S buccal morphology criteria, the epigrowth feeder was the most dominant type throughout the year, except February, when the non-selective deposit feeder increased and took over the top rank. The characteristics of nematode communities of phytal and sediment layer in the eelgrass bed was briefly compared.

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Some ecological information about deep-sea ophiuroids is reviewed, with some notes on their roles in deep-sea benthic communities and general ecological trends along the depth gradient. The ophiuroids are numerically important members in deep-sea benthic communities. Recently, many ecological studies have been carried out on deep-sea ophiuroids. The underwater photography has been used to elucidate life styles and feeding habits, and the quantitative analysis of the bottom photographs has clarified population densities and spatial patterns. Stomach contents of deep-sea benthic organisms have indicated that many ophiuroid species are omnivorous, and that ophiuroids are sometimes consumed by the other predacious organisms. Moreover, a few in situ experimental approaches have been applied to estimate their respiration. Thus, some examples have been obtained about food webs and energy budgets in deep-sea benthic communities. Reproduction and population dynamics were revealed by analysis of size-frequency distributions and gonads of seasonal samples, showing seasonal recruitment and annual synchronous reproduction for some species in the deep sea.

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The introduced spider crab, Pyromaia tuberculata, was originally distributed along the Pacific coast of southern North America. Its occurrence in Japanese coastal areas was first recorded in 1970, in and near Tokyo Bay, on the Pacific coast of central Japan. Thereafter, increase of abundance in that bay and some additional collection record of the crab in other regions were reported. To ascertain recent state of geographical distribution of the crab, a questinnaire was sent to the laboratories and stations of marine biology and fishery science covering whole Japan in winter, 1984. Geographical distribution of the crab along Japanese waters was determined by the result of the questionnaire. The crab was distributed along the Pacific coast of central Japan, eastern part of Seto Inland Sea, and a small inlet on the western end of Honshu, faced to Japan Sea. It tended to be abundant in organically polluted, large and shallow bays e. g. Tokyo Bay, Ise-Mikawa Bay and Osaka Bay. The informations about the initial place and time of introduction of the species, and process of spreading along Japanese waters were not obtained.

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Field observations on the population trends and life history of recently introduced spider crab Pyromaia tuberculata were made in organically polluted inner Tokyo Bay. The crab population was abundant through late fall to early summer at the deeper subtidal bottom where heavy oxygen deficiency and temporal extinction of benthic animals occurred every late summer. Egg-carrying females were found throughout the year. By aquarium experiments, negative logarithmic relationship was ascertained between incubation period of eggs and the water temperature. The incubation period varied from 7 days (26°C, summer) to 84 days (8.5°C, winter). The recruitment of young crabs was recorded in early spring, midsummer and late fall, but successful recruitment occurred only in late fall when the bottom environmental conditions improved and the adult density was low. Young crabs recruited in late fall were estimated to reach maturity and start breeding within three months. Adaptive significance of such life history traits of the crab to subsistence under organically pollluted unstable environment is discussed.

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OMORI KOJI, (Department of Biology, Faculty of Science, Ehime University). 1988. Preliminary report on the benthic communities in the mangrove area of Iriomote Island, Okinawa. Benthos Research (Bull. Jap. Assoc. Benthology) 33/34, 91-94. Community composition of macrobenthos and some environmental variables of bottom substrate were investigated in two mangrove areas of Iriomote Island, Okinawa, and the relationships between them were analyzed by the canonical correlation analysis method. The most important canonical correlation coefficient of environmental variables was concerned with particle size of organic detritus derived from mangrove litters, and the stations of two study areas were discriminated by the coefficient. One locality was characterized by coarse detritus fraction and the other was characterized by the finer fractions. Considerable number of macroherbivores directly consume mangrove leaves occurred only in the latter locality. The composition of benthic fauna, consumption and decomposition process of mangrove derived organic matter seemed to be different by locality, mainly influenced by topography and other habitat conditions.

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