Gammarid fauna of many station samples taken from Shijiki Bay were classified into association types based on the cluster analysis of species compositions, and the sediment types were also classified by the similarity analysis of granulometric compositions. A close correlation was found between the distribution of ten gammarid associations and that of four major sediment types in the whole area. In the inner part of the bay where the grain size composition of the habitat units shifted gradual, shift of faunal composition of gammarids in those areas was also gradual. Most of gammarid species have no significant correlations with organic matter content, nitrogen content and shell matter content of the sediment except for four species. The Ampeliscid -dominated community (community II including association types II₁ to II₉) occurred in the central part of the bay, especially, the most dominant species Byblis japonieus occurred on the various sediment types ranging from very fine to coarse sand, accompanying with characteristic subdominant species in different associations. Distinct segregation of sediment type utilization was observed among the species belonging to the same genus such as Ampelisca and Corophium. Distribution patterns of the gammarid associations in the bay are explained by mosaic patterns of sediment types, high correlation between gammarid distributions and sediment types, and by interspecific habitat segregation of some important species.

抄録全体を表示

The Ohta River flowing through Chugoku district empties with six branches into Hiroshima Bay situated in the northwest region of the Seto Inland Sea of Japan. The bottom fauna survey was conducted at stations established along a canal of the Ohta River and adjacent shallow marine area. A distinct transition of faunal composition was observed at a short distance between the river region and the sea out of the river mouth. In the canal, various taxonomic groups of brackish species and euryhaline ones of marine origin occurred, forming a very rich community. While, marine region in front of the river mouth harboured mainly polychaetes. The similarity analysis of community composition between sampling stations were highly suggestive of transverse formation of salt wedge. The faunal transition pattern was compared with those of the other rivers.

抄録全体を表示

Corophium volutator, a mud-flat amphipod, has a prolonged reproductive season from February to November in Amakusa, western Kyushu, and shows semi-lunar (high temperature conditions) or lunar (low temperature conditions) reproductive rhythmicity. The population density of this amphipod changes according to the rainy season, from June to July, and typhoon season, from August to September. Therefore, this period is the critical period, C. volutator shows semi-lunar reproductive cycle, i.e, synchronized reproductive activity. To evaluate the adaptative significance of this reproductive rhythmicity in unpredictable environments a simulation model of reproductive activity and asynchronous one are calculated under various assumptions. As a result, animals with synchronous reproductive activity can produce more progenies than those without synchronous reproduction under low population density and skewed sex ratio (males/females <1).

抄録全体を表示

Presently there is considerable controversy surrounding larval recruitment processes of the Japanese spiny lobster Panulirus japonieus. This is based primarily on the lack on other than occasional phyllosomes in the neighbour-ing coastal waters north of the Kuroshio. Purposes of this review paper are to inquire the reasons why very few of phyllosomes of P, japonicus have been obtained in the Japanese waters, This paper includes discussions as follows: (1) possible identification of several local populations in P. japonieus by using biochemical genetic techniques, (2) ecology of phyllosomes and pueruli in palinurid lobsters, (3) problems concerning larval recruitment processes in Florida's (P. argus) and Japanese (P. japonieus) spiny lobsters, (4) the sub-tropical gyre in the western North Pacific and the geographic distribution of P. japonieus, (5) hypotheses con-cerning (a) how newly spawned phyllosomes of P. japonieus quickly enter the Kuroshio and Countercurrent and the middle to late stages phyllosomes are retained there, then (b) how migratory pueruli of P. japonieus recruit to the juveniles and adults in the shallow waters, and (6) possible causes of yearly fluctuations of puerulus abundance within traps set in the shallow waters and stock-recruitment relationships.

抄録全体を表示

The intertidal amphipods, which were previously regarded as single species Melita koreana, were studied in the central part of the Inland Sea of Japan. As the result, occurrence of four species (M, koreana, M, rylovae and two unnamed species, sp. I and sp. II) were recognized. M, ryilovae was treated as synonym of U. koreana by Nagata (1965), however, the differences are valid throughout the ontogenetic development, no intermediate form was observed. The four species reported here are distinguishable by morphologyical differences in male gnathopod 1 and female coxal plate 6. The adult body size is also different by species. The amphipods have precopulate habit before mating. Though there was little difference in breeding behavior among the species, no interspecific precopula was observed in cross-breeding experiment. Active selective response of males to females suggested that the males discriminated the conspecific females. These four closely related forms are reproductively isolated each other by ethological mechanism, and should be evaluated as discrete species.

抄録全体を表示

Sediment meiofauna in and around the seagrass bed were quantitatively studied at Yojiro beach in Kagoshima city, south Kyushu. Sampling was carried out at three stations every 3 months from November 1982 to August 1983. The temporal variations in total density of meiobenthic higher taxonomic groups and the species composition of nematodes are described, and the similarity among stations examined. Nematodes, the most dominant group (74-99%), was studied in detail. Seventy three species were identified. The depth distribution of some dominant species was determined. Except for the deep burrowing species, Cobbia trefusiaeformis, which characterized the summer sample at stn.II, 75-85% of total nematodes concentrated in the upper 3cm of the sediment. The relation between the distribution of feeding types nematode species and the nature of sediment is discussed.

抄録全体を表示