DISTRIBUTION PATTERN OF OCYPODIDAE AND STORAGE FUNCTION OF ORGANIC MATTER BY Macrophthalmus japonicus IN ESTUARINE TIDAL FLATS

摘要

1) Five Ocypodidae species were observed on the seaward tidal flat. It was found that their distribution depended on tidal flowing and salinity. 2) Ocypodidae showed clear interactive habitat segregation even within one tidal flat related to variation of sediment characteristics. Furthermore, a model to predict the distribution of Ocypodidae could be proposed based on the quantification theory type Ⅱ using salinity, altitude, silt content, acid volatile sulfate contents and penetration resistance of sediment as habitat indices. As a result, the distribution of three dominant species could be predicted with an accuracy of 72 %. Therefore, this model would be useful to assess the impact of development on the estuarine environment and effects of restoration for the tidal flat. 3) It was indicated that Macrophthalmus japonicus would selectively feed on diatom from depositions. The population in the whole estuarine tidal flats (170 ha) was estimated to be approximately 120,000,000 crabs in August 2000. The storage values of aggregate carbon and TN were 6.78 ton carbon and 1.49 ton nitrogen respectively, and was equivalent to 0.06 % of the amount of TN discharged from the Yoshino River basin in a year. It was estimated that Macrophthalmus japonicus would purify 1.6% of daily TN of the basin during summer.