東京湾の潮間帯におけるムラサキイガイの付着,生長および死亡について

Abstract

Mussel (Mytilus edulis galloprovincialis LAMARCK) is the most important animal in the inter-tidal sessile fauna of Tokyo Bay. The settlement of young mussel to the mussel beds occurred during the period from March to September with the peak May to July in Tokyo and Yokohama Harbors, and occurred throughout the year with the peak May to August in Yokosuka Harbor. The growth and mortality were studied on the mussel population found on a horizontal plane (D. L.+1m) in the intertidal zone of Yokohama Harbor. The linear growth of shell length was found during the warm season (April to December), but the growth was almost absent during the winter. The annual variations in growth were illustrated for two different year mussels, i.e. the mean shell sizes of one yearage mussels settled in 1973 and 1974 were 33mm and 28mm, respectively. The life span of mussels after settlement was about two years. The monthly mortality rates of juvenile mussels (less than 20mm in shell length) settled in 1974 and 1975 were 25% and 55%. respectively. Increases of mussel biomass during the spring to summer and the fall were caused by growth in 0 and one year-age mussels of same year settlement, and decreases of the biomass occurred in August and January when the maximum solar radiation and colder weather seemed to contribute to mass mortality of mussels during the exposure to the air.