Present condition and conservation of snails and their parasitic cercariae on tidal flats in west Pacific region

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Snails living on tidal flats and their parasitic larval trematodes were examined at about 60 sites in Japan. Snail diversities varied from tidal flats, but very high at Gabei tidal flat and estuary of Oura River in Nago city (Amami-Oshima Island), Sone tidal flat in Kitakyushu city and estuary of Takori River in Saga Pref. Seventeen kinds of cercariae were found from all snails examined. Infection rates of cercariae were very high in Batillaria cumingii at Yuuto-cho in Hamamatsu city, in B.multiformis at Jougasawa in Mutsu city, in Cerithidea cingulata at Urauchi River of Iriomote Island and C.rizophorarum at Doki River in Kagawa Pref. Highest diversity (5 species) of cercariae were recorded in Yuuto-cho, Waka River in Wakayama city and Urauchi River. Indices representing diversity and rarity of snails and cercariae were calculated and especially high values were obtained at Gabei tidal flat, Urauchi River and Oura River. Consequently it is thought that those places are most valuable h … More abitats for brackish water trematodes and that they are the most important candidates for conservation. In Thailand, snails and cercariae were examined at about 100 sites and the highest infection rate 100% was recorded in C.cingulata at Ban Klong Klaeng in eastern coast. Total infection rates of C.cingulata were almost the same as those of C.djadjariensis, but in coexisting sites infection rate of one species was often higher than the other. Cercaria diversity was highest at Mangrove Research and Development Station in Phuket town. Moreover we conducted the survey at three sites before and after the Indian Ocean tsunami, but the significant changes in infection rates and cercarial fauna were not detected. In Korea snails and cercariae were examined at seven sites. Infection rates in B.cumingii in Saemangeum tidal flat was very high and thought to be a valuable place for brackish trematodes. However, the tidal flat was closed by banks and snails and their parasites died out. In Myodo Is., Yeosu-shi, diversity of snails was high, but their infection rate to trematodes was very low. Less