Saowapa Angsupanich

SEASONAL VARIATION OF PHYTOPLANKTON COMMUNITY IN THALE SAP SONGKHLA, A LAGOONAL LAKE IN SOUTHERN THAILAND

The phytoplankton in Thale Sap Songkhla was investigated at 2–3 month intervals from August 1991 to October 1993. The abundance of phytoplankton ranged from 1.4×106 to 1.3×109 cells m−3. A total of 6 divisions with 103 genera were identified as Bacillariophyta: 49 genera, Chlorophyta: 21 genera, Pyrrhophyta: 15 genera, Cyanophyta: 12 genera, Chrysophyta: 3 genera and Euglenophyta: 3 genera. Although phytoplankton abundance was distinctly greater in the first year of study (August 1991–June 1992) than in the second year (August 1992–October 1993), their patterns are similar: 2 peaks yearly. The peaks of phytoplankton occurred in the heavy rainy season (northeast monsoon) and the light rainy season (southwest monsoon). The main bloom was found during December–January, with a predominance of blue-green algae (e.g. Aphanizomenon andPhormidium) and green algae (e.g. Eudorina). Their species composition also increased, an effect of the large amount of rainfall resulting in low salinity during the northeast monsoon. The minor bloom was produced by diatoms during June–July when water salinity was moderate to seawater. Both phytoplankton numbers and species composition were high. However, unpredictably heavy rainfall during the southwest monsoon period may reduce diatom production due to rapid immediate replacement by blue-green species. Besides salinity concentration, a low total nitrogen: total phosphorus (TN: TP) ratio tended to support the growth of blue-green algae. The diversity of phytoplankton was lowest in the heavy rainy period.

Description of three species of Halmyrapseudes (Crustacea: Tanaidacea: Parapseudidae), with a discussion of biogeography

We describe Halmyrapseudes gutui sp. nov. from a mangrove area on Lidee Island, southern Thailand. This species closely resembles H. cooperi, H. killaiyensis, and H. thaumastocheles, but differs in having the lacinia mobilis with three teeth, and the pereopod 1 carpus with 0,1 or 1,1 ventral simple setae proximal to each spiniform seta. We redescribed and synonymized two species of questionable affiliation, Apseudes cooperi and A. digitalis, placing them in Halmyrapseudes, and partly redescribed Halmyrapseudes killaiyensis. Halmyrapseudes and Pseudohalmyrapseudes have disjunct distributions. Halmyrapseudes is similar in distribution to two freshwater fish taxa whose distributions are considered to reflect the breakup of Gondwana and subsequent continental drift. Pseudohalmyrapseudes occurs around Australia, and its distribution seems to be separated from that of Halmyrapseudes by Wallaces Line or Huxleys Line, which are distributional barriers for both terrestrial organisms and an amphidromous shrimp. The adjacent distributions and morphological similarities suggest that Halmyrapseudes and Pseudohalmyrapseudes are sister taxa.