Diversity and seasonal variations of plankton in coastal waters receiving salt pan effluents off Thoothukudi, south-east coast of India

The present investigation deals with the assessment of diversity and seasonal variations of plankton in coastal waters receiving salt pan effluents (station 1) in comparison to a reference site (station 2) of apparently unpolluted water. The species diversity of phytoplankton was comparatively more in station 1as compared to station 2 where as the density of phytoplankton was found to be lower in station 1 (48 - 177 cells l(-1)) compared to station 2 (44 - 565 cells l(-l) ). The maximum and minimum density were recorded during summer and monsoon season respectively. With regard to zooplankton composition, station 2 recorded higher numbers of species (42) followed by station 1. In both stations, maximum density of zooplankton was observed during summer. Zooplankton density ranged from 9,800 (November, 2011) to 70, 800 no. m(-3) (May, 2012) at station 1 and 15,400 (December, 2011) to 2,07,000 (May, 2012) at station 2. The species richness index D for phytoplankton varied from 0.43 to 0.76 and 0.79 to 2.05 in station 1 and 2 respectively. The species richness index D for zooplankton in station 1 and 2 varied from 0.99 to 1.63 and 1.09 to 3.84 respectively. The species diversity index ('H') for the phytoplankton in station 1 and 2 varied from 0.75 to 1.37 and 1.06 to 1.95 respectively. The species diversity index ('H') for the zooplankton in station 1 and 2 varied between 1.64 to 2.28 and 1.66 to 3.25 respectively. The present investigation showed that the plankton diversity of coastal waters receiving salt pan effluents (station 1) was influenced by seasonal variations as compared to the unpolluted coastal waters of station 2.