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[Species composition and abundance of decapod crustaceans were studied in the waters off Geoje Island, located off the southeastern coast of Korea, using a shrimp beam trawl from November 2000 to October 2001. Water temperature above the sea bottom was lowest ( 25°C) in August. A total of 196,149 individuals of 41 species from 17 families and 3 suborders was observed. Shrimps (Macrura Natantia) accounted for 23 species, hermit crabs (Anomura) and crabs (Brachyura) for 7 and 11 species, respectively. Crangon hakodatei was the most abundant species both in terms of overall number and biomass. Total biomass showed three peaks during the study period. The first peak in January was due to C. hakodatei and Charybdis bimaculata. The second and third peak were due to C. hakodatei and Palaemon gravieri. Cluster analysis, based on monthly abundance data of the 12 dominant species, showed that the species could be separated into three different groups: resident, seasonal, and temporary. The decapod community structure in the study area was predominantly affected by the resident group. La composition specifique et l'abondance des Crustaces Decapodes ont ete etudiees dans les eaux de l'ile Geoje, situee pres de la cote sud-est de la Coree, a l'aide d'un chalut a crevette entre novembre 2000 et octobre 2001. La temperature de l'eau du fond a ete la plus basse en mars ( 25°C) en aout. Au total 196149 individus appartenant a 41 especes de 17 familles et 3 sous-ordres ont ete observes. Les crevettes (Macroures Natantes) sont representees par 23 especes, les Bernard l'Hermite (Anomoures) et les crabes (Brachyoures) par 7 et 11 especes respectivement. Crangon hakodatei a ete l'espece la plus abondante, a la fois en termes de nombre d'individus et de biomasse. La biomasse totale a montre trois pics durant la periode etudiee. Le premier pic, en janvier etait du a C. hakodatei et Charybdis bimaculata. Le second et le troisieme pics, etaient dus a C. hakodatei et Palaemon gravieri. L'analyse des groupements, basee sur les donnees d'abondances mensuelles des 12 especes dominantes a montre que les especes pouvaient etre separees en 3 groupes differents: les residentes, les saisonnieres et les temporaires. La structure de la communaute des Decapodes dans la zone etudiee est conditionnee de facon predominante par le groupe des especes residentes., Species composition and abundance of decapod crustaceans were studied in the waters off Geoje Island, located off the southeastern coast of Korea, using a shrimp beam trawl from November 2000 to October 2001. Water temperature above the sea bottom was lowest ( 25°C) in August. A total of 196,149 individuals of 41 species from 17 families and 3 suborders was observed. Shrimps (Macrura Natantia) accounted for 23 species, hermit crabs (Anomura) and crabs (Brachyura) for 7 and 11 species, respectively. Crangon hakodatei was the most abundant species both in terms of overall number and biomass. Total biomass showed three peaks during the study period. The first peak in January was due to C. hakodatei and Charybdis bimaculata. The second and third peak were due to C. hakodatei and Palaemon gravieri. Cluster analysis, based on monthly abundance data of the 12 dominant species, showed that the species could be separated into three different groups: resident, seasonal, and temporary. The decapod community structure in the study area was predominantly affected by the resident group. La composition specifique et l'abondance des Crustaces Decapodes ont ete etudiees dans les eaux de l'ile Geoje, situee pres de la cote sud-est de la Coree, a l'aide d'un chalut a crevette entre novembre 2000 et octobre 2001. La temperature de l'eau du fond a ete la plus basse en mars ( 25°C) en aout. Au total 196149 individus appartenant a 41 especes de 17 familles et 3 sous-ordres ont ete observes. Les crevettes (Macroures Natantes) sont representees par 23 especes, les Bernard l'Hermite (Anomoures) et les crabes (Brachyoures) par 7 et 11 especes respectivement. Crangon hakodatei a ete l'espece la plus abondante, a la fois en termes de nombre d'individus et de biomasse. La biomasse totale a montre trois pics durant la periode etudiee. Le premier pic, en janvier etait du a C. hakodatei et Charybdis bimaculata. Le second et le troisieme pics, etaient dus a C. hakodatei et Palaemon gravieri. L'analyse des groupements, basee sur les donnees d'abondances mensuelles des 12 especes dominantes a montre que les especes pouvaient etre separees en 3 groupes differents: les residentes, les saisonnieres et les temporaires. La structure de la communaute des Decapodes dans la zone etudiee est conditionnee de facon predominante par le groupe des especes residentes.]

鹿児島湾の小型底曳網漁船に同乗して採集したヨツトゲシャコSquilloides leptosquilla を用いて, 産卵期および食性を調べた。生殖腺指数の解析結果より, 本種の雌の成熟サイズは頭胸甲長10mmで, 産卵期は5～9月, 産卵盛期は7～9月と推定できた。胃内容物の観察により, 本種は肉食性捕食者で主にエビ類を捕食することがわかった。特に, 鹿児島湾における水産上の有用種であるナミクダヒゲエビSolenocera melantho を捕食している個体の出現頻度が高かった。

Examination of the stomach contents of the Japanese mantis shrimp Oratosguilla oratoria showed that this species is a very intensive predator on the Macrura which is a principal component of the benthic megalofaunal community. Thus, the mantis shrimp, by feeding largely on the Macrura, may have a major influence on this community structure in Hakata Bay. The shrimp was also revealed to be an intensive predator on the Pelecypoda despite underestimation of preda-tion intensity, based on the stomach contents, because of its shell-smashing behaviour. Further-more, this study showed that many Macrura were captured during September and November by the mantis shrimp and that female shrimp of reproductive sizes also consume many Pelecypoda, As a prey species, mantis shrimp themselves were found infrequently in the digestive tracts of other predators.

Samplings of decapod crustaceans were conducted in the Yukinoura River to estimate the influence of a dam having no fishway on the distribution of these animals. Eight decapods were collected from freshwater area. Two of them, Geothelphusa dehaani and Neocaridina denticulata, were landlocked species, and the others were amphidromous or catadromous species. The present fauna can not be compared directly with the fauna before the dam construction because of the absence of comparable studies. Comparing the species composition from respective sampling stations, however, the influence of the dam on their distributions can be estimated as follows: (1) Caridina typus, Macrobrachium japonicum and Macrobrachium formosense could no longer get by the dam into their former habitats. (2) Eriocheir japonicus could reach the dam lake but stopped migrating upstream into its former habitat. (3) Caridina leucosticta had the upper part of its former habitat destroyed by the dam and dam lake. (4) N. denticulata had an expansion of distribution because of the still water environment in the dam lake. (5) G. dehaani was unaffected by the dam. At first glance, Caridina japonica, a resident in the uppermost stream, can be categorized in the fifth category, but its population density seems to have decreased after the completion of dam in 1976.