Population Dynamics of Sessile Bivalves Mytilus galloprovincialis and Xenostrobus securis in Hyper Eutrophicated Bay, Japan

This study was conducted to clarify the population dynamics of the two predominant bivalves, Mytilus galloprovincialis and Xenostrobus securis, in Dokai Bay, Japan. Quantitative sampling of sessile animals and monitoring of water quality in Dokai Bay, were carried out from 1991 to 1992. We applied cohort allometry to these species to evaluate their population dynamics. These bivalves predominated on the vertical walls of the intertidal zone, and its maximum standing stock reached 18.3kg/m2 for M. galloprovincialis and 10.6kg/m2 for X. securis. With respect to M. galloprovincialis, it is suggested that most of the population inhibiting the inner bay will be spoiled by anoxic water in summer, and the population which is inhabiting the bay-mouse will act as a source population to support the whole population in Dokai bay. On the other hand, X. securis dominated the inner part of the bay, and a negative relationship was found between X. securis biomass and the number of sessile animal species in Dokai Bay. In this study, we found typical population dynamics of the sessile animal community in the eurtophicated area.