Differences in bivalve assemblages of artificial and natural tidal flats in inner Tokyo Bay

Abstract

To evaluate the ecosystem services of an artificial tidal flat, bivalves at six artificial and five natural tidal flats were sampled in inner Tokyo Bay. Moreover, the most dominant species, the Manila clam Tapes (Ruditapes) philippinarum, were reared using in situ enclosure cages to determine the environmental factors affecting bivalve community structure. There were no differences between the bivalve assemblages of artificial and natural tidal flats. The results showed that the bivalve assemblages were determined not by sediment characteristics of a tidal flat but by the location in the bay. The dominant species started with the Manila clam in the southern part, which has a direct connection with the Pacific Ocean, followed by Mactra veneriformis, Musculista senhousia, and Xenostrobus securis with distance to the mouth of the bay. The most important environmental factors responsible for the bivalve community structure in the bay were salinity and hypoxia. In the southern part of the bay fertile Manila clam populations provide ecosystem services of collecting clam "Shiohi-gari". On the other hand, in the northern part of the bay where the coastal population density is high, tidal flats provide ecosystem services of coastal stability by wave dissipation or landscape benefits.