Change in the Composition of Molluscan Shell Assemblage Washed up on the Shore in Amami Island, Japan

Abstract

Molluscan shells washed up on the shore in Amami Island, south of Kyûshû were quantitatively sampled by beachcombing and sand-sorting on the strandline in 1979 and 1988, between which a lagoon near the sampling sites was landfilled for construction of a new airport. In all the samples, the most dominant part was occupied by gastropods, most of which were free-living epiphytes in the intertidal or subtidal zone. Between the two years, the proportions of interstitial detritus feeders, e.g., Caecids, and grazers of colonial animals, e.g., Triphorids, decreased. Data on the composition of the number of individuals per family were used for a principal component analysis. The trend in the variation of the shell assemblages between the two years coincided with the gradient of environmental disturbance. This suggests that changes in the composition of molluscan shell assemblage resulted from deterioration of the coral reef ecosystem, caused by human activities.