Estimation of Crustacean Habitat Distribution by Counting Their Burrow on Amparu Tidal Flat, Ishigaki Island

AMPARU is a large tidal lagoon located on the west coast of Ishigaki Island, where a variety of small crabs range over. In these thirty years, however, accumulation of red clay from the watershed has been changing the topography and the hydraulic characteristics of the lagoon, and then changing the environments for the crabs to habitat there. This paper presents a result of a field survey that is the basic stage of a study to understand the special distribution of crabs in relation with the conditions of bed materials and hydraulic characteristics in the lagoon. First, spacial distribution of five kinds crabs and there burrows are clarified through photograph analysis and quadrat survey, and it is concluded that the burrow's distribution can be an effective information to estimate the distribution of three kinds of crabs who make burrows. And then, it is found that the habitat distribution of each kind of crab can be highly related to their living characteristics, such as territorial competition , burrow takeover, seasonal torpor and efficiency of nutrition as well as environmental conditions such as grain distribution of bed materials, organic matter content and submergence frequency.