Tidal Flat Macrofauna in the Inner Part of Ariake Bay.

Abstract

The macrofauna of three estuarine tidal flat areas at the mouth of the Chikugo River, Rokkaku River, and Shiota River in the inner part of Ariake Bay is described. Sampling was done from a boat during high tide using a Smith-McCintyre grab sampler (22.522.5 cm) at 11 stations in each area in December, 2005, and May and August, 2006. Sediment was sieved through a 1-mm mesh screen and the residue was fixed, stained with Rose Bengal, and sorted. Multivariate analyses showed that community structure di#ered significantly between the tidal flats. This was mainly due to di#erences in the abundance of the semelid bivalve Theora fragilis, capitellid polychaetes, the arcid bivalve Scapharca kagoshimensis, the venerid bivalve Ruditapes philippinarum, and stenothyrid gastropods Stenothyra spp. The distribution of endangered species and invasive species also di#ered between tidal flats. The invasive corbulid bivalve Potamocorbula laevis and nassariid gastropod Nassarius sinarus, and the endangered tellinid bivalve Tellina iridescens, arcid bivalve Tegillarca granosa, and camptandriid crab Camptandrium sexdentatum occurred mainly in the mudflats of the Rokakku River and/or Shiota River estuaries, while the brachiopod Lingula anatina and mytilid bivalve Modiolus metcalfei were mainly distributed in the Chikugo River estuary. Di#erences in sediment grain size were likely the main factor resulting in di#erences in the macrofauna and the distribution of endangered species among the tidal flats.