LIFE-HISTORY OF THE GHOST SHRIMP, CALLIANASSA-JAPONICA ORTMANN (DECAPODA, THALASSINIDEA), ON AN INTERTIDAL SANDFLAT IN WESTERN KYUSHU, JAPAN

Growth, density, survival, and reproduction were examined for the popu lation of the ghost shrimp, Callianassa japonica Ortmann, inhabiting a n intertidal sandflat in western Kyushu, Japan, based on samples colle cted from May, 1989 to April, 1991. During the breeding season (June-O ctober) each year, there were two discrete periods of egg production b y females. The post-larval settlement, with a time-lag of 1-1.5 months (brooding plus larval developmental periods), generated two major rec ruitment cohorts, occurring in July-August (1st cohort) and September- November (2nd cohort). The higher growth rate of individuals after rec ruitment in the 1st cohort enhanced the separation of the two cohorts. Between sexes, the subsequent life history patterns and population ch aracteristics were, for the most part, similar. In females, the majori ty of individuals of each of the two cohorts matured after approximate ly one year, respectively, at around a 20-mm total body length, and a portion of these cohorts survived as a fused cohort until June of the second year, breeding again prior to dying off by the end of September . The pattern of growth was an indetermined type. For each of the two cohorts, the growth rates changed at two transition points of their li fe history, at around the beginning of their two breeding seasons. The growth rate for the 1st cohort slowed down at the first transition po int, while that for the 2nd cohort speeded up there. This led to the a pproach and fusion of the two cohorts near the second transition point , when growth stopped. During periods other than the breeding seasons, high survival rates were exhibited by the two cohorts. During the fir st breeding season, a significantly low survival rate was observed for the 1st cohort, but not for the 2nd cohort. The degree of participati on in breeding activity may be responsible for the above differences b etween cohorts. In the two male cohorts, while the cost of reproductio n did not reduce the growth rates during the first breeding season, it lowered their survival rates more severely compared to those of femal es. This may be responsible for the slightly female-biased sex ratio i n the population (1.06:1). The density of the population as a whole wa s stable throughout the study period, with the mean +/- SD being 901 /- 157/m(2) (n = 27); the adult population declines during the breedin g seasons were effectively replenished by recruitment each year. (C) 1 997 Elsevier Science B.V.