Post-Settlement Processes Determining the Features of Bivalve Assemblages in Tidal Flats

Abstract

The mouths of two rivers in Japan, the Ano and the Shitomo, are adjacent to each other but show a marked difference in their bivalve assemblages on the tidal flats. From the results of a four-year field investigation on the densities of larvae and recruitants of three dominant bivalves (Nuttallia olivacea, Ruditapes philippinarum, Musculista senhousia), we sought to see whether pre- or post-settlement processes are the important factors determining the features of the bivalve assemblages in each river. They were found to be determined basically by post-settlement processes. However, in some years, they were determined after larval recruitment (>1.0mm in shell length), and in other years immediately after the larvae had settled on the tidal flats or after the bivalves had reached a certain size but before larval recruitment.