Spatial variability in the phytoplankton community along a transect across the Similan Islands in the Andaman Sea: A case study 2007-2008

The marine phytoplankton community was studied between October 2007 and March 2008 along a transect across the Similan Islands in the Andaman Sea during the southwest and northeast monsoon seasons. Seawater was collected from 11 stations on the transect. At least 146 species belonging to 68 genera in 37 families and 11 orders of marine phytoplankton were identified by microscopic observation. Diatoms were the major group of dominant phytoplankton particularly at depths in the study. Cyanophyta, particularly Trichodesmium spp., was the dominant group but the species diversity was maximal for dinophyta and heterokontaphyta from both monsoon sampling periods. The most diverse genera of dinoflagellate were Ceratium, Dinophysis, and Protoperidinium, while a high variety of diatom genera were Rhizosolenia and Chaetoceros. The relative results between the phytoplankton group and environmental parameters revealed that phytoplankton was strongly affected by salinity and silicate concentration during the southwest monsoon, while the availability of photosynthetically active radiation was significantly correlated with seasonal succession during the northeast monsoon