Brackish-water mollusks of Surat Thani Province, southern Thailand.

Brackish-water mollusks inhabiting the mangrove areas along the Gulf of Thailand of Surat Thani Province were investigated for distribution, abundance and natural infections. Nine families and 32 species of brackish-water snails were recovered from 14 sampling stations. Species belonging to the genus Ceritidea of the family Potamididae were mainly examined and Cerithidea (Cerithideopsilla) Cingulata, C. (C.) djadjariensis, and C. (Cerithidea) charbonnieri were naturally infected with 2 types of trematode cercariae, and one which was undetermined. C. (C.) cingulata had the highest infection rate (38.5%). Viewing two snail communities, the first community on the mainland and the second on Samui Island in Surat Thani Province, 28 brackish-water mollusk species were present on the mainland, 15 species were evident on Samui Island, and 11 snail species were common to both the mainland and Samui Island. Measurement of community similarity based on species presence revealed an index of similarity of 0.51. Concerning land use by the local people in the station areas investigated, brackish-water snails in Surat Thani Province are facing habitat degradation by human use.