Plankton as indicators of coastal water bodies during south-west to north-east monsoon transition at Kalpakkam

In the coastal waters of Kalpakkam, a water body characterized by high sali nity, rich nutrients and low temperature (southern-sub surface water SSW) w as seen during the early half of September when the pole-ward current preva iled. This was replaced by low saline, low nutrient and relatively high tem perature water (northern-surf;tce water NSW) during early October when the current was equator-ward, This reversal in current direction is induced by the north-east monsoon winds during the SW to NE monsoon transition. It is also observed that SSW in the Kalpakkam coast during the later half of Sept ember was characterized by the presence of pennate diatoms Nitzschia closte rium, Asterioilella glacialis and Thalassionema nitzschiodes. However, NSW in this coast in early October is characterized by the presence of centric diatom Skeletonema costatum. The two water bodies also have a characteristi c zooplankton population, the SSW is rich in meroplankton and the NSW is po or in meroplankton. Thus, the pennate diatom N. closterium, A. glacialis an d T. nitzschiodes would be considered as indicators of SSW and centric diat om S. costatum as the indicator of NSW.