The dynamics of the molluscan community in the soft bottom of Hakata Bay, Japan, with special reference to the summer stratification period

Abstract

The dynamics of the molluscan community inhabiting the soft bottom of Hakata Bay, north Kyushu, was studied during May to October, 1984. Distribution of animal density depended mainly on two dominant species, Theora Zubriea and Museulista senhousia. The center of mollusc distribution moved out from the inner waters of the bay and stayed in the middle waters during the summer stratification period when the dissolved oxygen in the bottom water diminished. The center returned to the inner waters when dissolved oxygen returned to higher levels. The community structure in various parts of the bay was studied before, during and after the strati-fication period. The community structure changed in relation to the range of fluctuation and to th.e minimal values of dissolved oxygen concentration. The similarity indices among the communities from various waters also changed seasonally. Two molluscan communities sometimes had similar structure but the formative processes may not have been the same. Different oxy-gen levels affect the process of community formation.