| Summary: | A bimonthly investigation of amphipod crustaceans in the Upper Songkhla Lagoon from April 2003 to February 2004 was undertaken to determine the abundance and species richness. The mean density of amphipods among stations ranged from 233 to 4937 ind.m-2, while the monthly densities ranged from 600 to 3620 ind.m-2. A total 10 families, 14 genera and 16 species were identified. The diversity among stationsranged from 2-12 species while varying from 8-15 species during the different months. Kamaka cf. taditadi is the most dominant amphipod with 89.2% of total (max. 16486 ind.m-2) in December. It distributed widely and in every sampling month. Photis longicaudata (36-338 ind.m-2) Grandidierella taihuensis (28-65 ind.m-2) Cerapus sp. (3-95 ind.m-2) and Perioculodes cf. acuticoxa (19-54 ind.m-2) distributed widely in all months but with lower densities. The other 11 species were occasionally found and had narrow distribution with low densities (< 20 ind.m-2). The density and diversity of amphipods were higher at the shallower stations nearby the bank (mean depth 1.1 m.) than at the deeper stations in the middle area (mean depth 2.5 m.). The species richness among seasons was not different but the density tended to increase in the rainy season in December and markedly decrease in the post-rainy season in February. The best fitting of the environmental variables to explain the amphipod community pattern of the Upper Songkhla Lagoon for 6 months was a 4-variable combination of pH, salinity, %sand and %organic carbon and a 3-variable combination of depth, DO and %sand for 11 stations (harmonic rank correlation coefficient, ρw = 0.56 and 0.51 respectively).
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