Abstract:
Ecological study of polychaetes in organic enriched condition in Pak Phannang Bay, Nakhon Si Thammarat Province was carried out during dry season in May, 2007 and wet season in October, 2007. The study area was divied into 17 stations. Macrobenthic diversity of 89 species 13 taxonomic groups were recorded in the area. Polychaetes, mollusk and crustaceans were the dominant groups. Rich diversity were recorded in the mangrove forest. Polychaetes of 39 species from 19 famillies were recorded from the area Namalycastis cf. indica and Heteromastus sp.A were dominant in the mangrove forests and mangrove creeks. Dendronereis pinnaticirris and Prionospio (Minuspio) japonica were abundant in thd Pak Phanang river while Nephtys (Nephtys) capensis, Mediomastus sp.A and Sabellidae sp.A were found to dominate the bay area. Polychaetes assemblage can be used as indicator species of organic enriched condition in the Pak Phanang Bay. The ratio between the three dominant benthos, revealed that polychaetes were the most dominant benthos in the area indicating the organic enriched condition in the bay. The first group was the benthic community associated with high organic content consisted of errantia namely Ceratonereis burmensis, Dendronereis pinnaticirris, Namalycastis cf. indica, Nephtys (Nephtys) capensis, Alglaurides sp.A and sedentaria namely Sabellidae sp.A, Heteromastus sp.A, Neomediomastus sp.A, Neoheteromastus sp.A, Mediomastus sp.A, Notomastus sp.A, Capitella sp.A, Capitella sp.B, Pulliella sp.A, Prionospio (Minuspio) japonica, Prionospio (Minuspio) multibranchiata, Cossura sp.A, Sabellidae sp.A, Ampharetidae sp.A The area in the Pak Phanang Bay showing the organic enriched conditions were Pak Phanang river in front of the Uthokvibhajprasid Dam and the mangrove plantation on the eastern side of the bay and The latter group consisted of errantia namely Aphrodotidae sp.A, Lepidonotus sp.A, Leonnates cf.persica, Nereis cf. persica, Nephtys (Nephtys) capensis, Marphysa cf. depress, Diopatra sp.A, Goniada sp.A, Glycera sp.A, Sigambra sp.A and sedentaria namely Sabellidae sp.A, Scyphoprotus sp.A, Mediomastus sp.A, Pseudopolydora sp.A, Prionospio (Prionospio) malayensis, Prionospio (Prionospio) depauperata, Scoloplos (Leodamous) sp.A, Haploscoloplos sp.A, Sabellidae sp.A, Cirratulus sp.A, Sternaspis scutata associated with moderate organic content sediment in mangrove creek and the bay. Namalycastis cf. indica, Neomedimastus sp.A, Neoheteromastus sp.A, Prionospio (Minuspio) japonica and Ampharetidae sp.A were proposed as indicator species of organic enriched condition. In determining the organic enriched condition in the Pak Phanang Bay, concluded from the ratio of dominant benthic groups, indicator species/groups and AZTIs Marine Biotic Index (AMBI) indicated that Pak Phanang river closed to the dam and the mangrove plantations on the eastern side of the bay were highly disturbed by the organic enriched condition than the Pak Phanang river along the western mangrove plantations and outside the Pak Phanang Bay.