Islands of Mytilus edulis as a habitat for small intertidal animals: effect of Mytilus age structure on the species composition of the associated fauna and community organization

Community structure of the associated animals of low intertidal patches of Mytilus edulis L. with different age structure was investigated at Asamushi, northern Japan.Each patch was composed of similar components i.e. live M. edulis, byssal threads, shell fragments, sediments, algae and associated animals.The amounts of sediments, shell fragments and byssal threads were greater in the periphery (MP) and central part (MC) of adult mussel patches than in patches of young (Y) and old (0) mussels.Total organic matter within sediments increased in the following order: 0, MC, MP and Y. Algal growth was luxuriant in Y and this supported abundant amphipods.Species richness was higher in older patches and species diversity (H') and equitabihty (J') were higher in MP and MC than in Y and 0. Sediments, shell fragments and byssal threads seemed to play an important role in increasing heterogeneity of environments and thus species diversity.Similarities in species compositions among MP, MC and 0 were high, but those between Y and other patches extremely low.This fact is probably caused both by the presence of a large number of epiphytic animals in Y and the difference in the composition of creeping fauna among the patches.Based on these results, the processes controlling community organization of Mytilus islands are discussed.