Vertical distribution of juvenile sea cucumber Apostichopus japonicus in a mesocosm experiment

Abstract

Early life history of the sea cucumber Apostichopus japonicusis important for developing methods forstock management and enhancement. However, information on the ecology of juvenile sea cucumbers in the wild is scarce, partly because of their low density. We investigated their diel change in vertical distribution in an adventitious mesocosm containingjuvenile sea cucumbers in the yard of the Maizuru Fisheries Research Station, Kyoto University.The density of A. japonicusjuveniles in shallow water was higher than in deepwater. The profiles of the water temperature and salinity were relatively uniformthroughoutthe water column, while photon strength was higher in shallow water in daytime. This result shows that juvenileA. japonicussea cucumbers have negative geotaxis despite havingnegative phototaxis. In field observations in Maizuru Bay, there were no juveniles at shallow sites, such asshores, suggesting that other environmental factors