中海における二枚貝群集の特徴と干拓堤防建設により隔てられた汽水域の変化

抄録

Bivalve community structure and its relation to the environmental factors in Lake Nakaumi, southwest Japan were examined for the surveyed data of 1997 and 2006. The brackish mussel Musculista senhousia was the predominant species of Lake Nakaumi in both years. Lake Nakaumi was divided into two areas, Honjo Area and Nakaumi Area, by the construction of reclamation dikes in the 1970s. The community and environmental features of the two areas were different. The bivalve community of Honjo Area was quite simple, while that of Nakaumi Area had some varieties. The homogeneity of salinity in Honjo Area was supposed to be the reason for the simple community structure. The bivalve community in Lake Nakaumi was divided into four types. These types were influenced by the frequency of the dominant species, primarily Musculista senhousia, and secondarily other dominant species. The spatial distribution of the community types changed from 1997 to 2006, and the area of no bivalves markedly increased in Honjo Area. The organic material of the sediment in Honjo Area apparently increased after the construction of dikes. This was supposed to increase the consumption of dissolved oxygen and expand the area of anoxia and no bivalves in Honjo Area.