A STUDY ABOUT RELATION OF RIVER WALL STRUCTURE AND TAIDAL BIOTA DISTRIBUTION IN YOSHINORIVER ESTUARY, AND A SUJETION OF NEW RIVER WALL USING THE RESULTS OF THIS STUDY.

Abstract

In order to grasp the relation between river wall structure and tidal biota distribution at a tidal river ,we surveyed 4 types of river wall structure (dry stone pitching, environmental conservation type, basket block, megaliths pitching) at the tidal area in Yoshino River which flows through the eastern paret of Shikoku Island in Japan. Distribution of tidal biota (Crassostrea gigas、Xenostrobus secures, Grapsoidea ,Caulacanthus okamurai) was observed .Tidal biota were more common at clearance gaps than the surface of river wall because gaps serve a function to maintain wet condition. Japanese oyster (Crassostrea gigas) and crabs (Grapsoidea) were more prevalent at the basket block than the other types of river wall, whilst Xenostrobus secures were less common at the basket block than the other types of river wall. Based on these results we suggest a new improved basket block for breeding Japanese oysters and crabs. And we suppose that this new river wall will control the distribution of the non-indigenous Mytilid Bivalve Xenostrobus which are prevalent in tidal rivers.