Results (
Thai) 1:
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DISCUSSIONSurat Thani Province in southern Thailand is richin brackish-water snails. In this investigation, 32species of brackish-water mollusks were found alongthe Gulf of Thailand (Table 2). Comparison of thisinvestigation with Brandt’s report (1974), and with theexception of unidentified species of Stenothyra,showed that 25 species collected were commonlypresent in the provinces of Thailand, 5 species wererare (present in some provinces of the country), and 1species was very rare (known only from Surat ThaniProvince) (Table 6).It is noteworthy that some species that had not beenpreviously found in Surat Thani Province wereobtained in this study – for example, Littorinopsismelanostoma of Chon Buri (Table 6). In contrast, manyof the rare species named in Brandt’s investigation,were not found in this study – for example, Neritina(Vittoida) variegata of Surat Thani and Clenchiellamicroscopica of Rayong, Chanthaburi, Trat, Bangkokand Surat Thani provinces.Table 3 demonstrates the fundamental unit(species) of the natural community actually existingin nature, during the time of the investigation andamong a variety of environmental stations. Amongthese brackish-water snails, Neritina (Dostia) violaceawas the most common species since it was found in 11stations (Tables 2 and 3). With the results obtained,more specific studies of the quantitative ecology ofthese snails are needed to confirm these findings.The brackish-water snail Cerithidea that was
most sensitive to trematode infection was C.
(Cerithideopsilla) singulata. Since the second type of
cercaria seemed to be a human parasite, it will be
identified after determination of the DNA sequences.
It is also interesting to note that high infection rates of
C. (C.) cingulata were recorded in stations 10 and 11.
Both stations are disposal areas for solid wastes with
poor sanitation, and many kinds of wastes including
human feces were found in station 11 (Table 1). Those
facts mean that life cycles of some trematodes have
been well maintained between final hosts and
intermediate hosts. Therefore, field collection of
Cerithidea species for further study is recommended.
Distributional relationships of brackish-water snail
species on the mainland and on Samui Island had
moderate similarity, with a calculated index of
similarity of 0.51 (Table 5). The information available
showed that the nature of brackish-water snail
communities of Surat Thani Province, between the
mainland and Samui Island, featured some similarity,
but not high similarity. Concerning land use by the
local people in the station areas investigated (Table
1), the brackish-water snails of Surat Thani Province
are facing degradation of habitat by human use. Thus,
brackish-water snails may be an indicator for studying
environmental health impacts in the future.
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