Seasonal and Interannual Variations in Biomass and Abundance of Megabenthos in Ise Bay, Central Japan

Abstract

Abstract: Due to recent eutrophication, oxygen-poor water develops annually near the bottom of Ise Bay, central Japan, in summer to autumn. This study examined seasonal and interannual variations in the abundance, biomass and distribution of megabenthos in the bay over a 7-year period to see if they were affected by this oxygen-poor water. The biomass of megabenthos, as well as the abundance/biomass of the dominant megabenthos species, drastically decreased during warm periods when oxygen-poor water developed, and increased from autumn to spring of the following year when oxygen-poor water no longer occurred. Seasonal variations in the spatial distributions of dominant species changed closely with the development of oxygen-poor water. The dominant taxa among the megabenthos(mainly echinoderms and crustaceans)and the dominant species within each dominant taxon changed drastically during the study. For crustaceans, the dominant species from 1996 to 1998(Paradorippe granulata and Cancer gibbosulus)differed greatly from those dominant from 1993 to 1994(Carcinoplax vestita, Oratosquilla oratoria and Charybdis bimaculata). This change may have been related to the matching/mismatching of spawning and larval recruitment events of each dominant taxon or species with the development and dissolution of oxygen-poor water in the bay.