Nutrients and phytoplankton dynamics in the fishing grounds off Tiruchendur coastal waters, Gulf of Mannar, India

Nutrients and phytoplankton dynamics in the traditional fishing grounds off Tiruchendur coast, Gulf of Mannar, India revealed a clear seasonal trend influenced by prevailing monsoon system in east coast of India. A total of 73 species of phytoplankton were identified from the fishing grounds, revealed higher abundance in summer months compared to other seasons. Among the three stations, maximum phytoplankton abundance was recorded in station 2 followed by stations 1 and 3. The phytoplankton abundance ranged from 2.85 x 10(4) to 6.34 x 10(4) cells/l, with higher and lower value observed during summer and post monsoon season respectively. Chl-a showed similar seasonal trend with phytoplankton abundance and fluctuated from 0.4 to 6.8 mg/m(3) with high concentrates were recorded during summer. Primary productivity was ranged from 13.8 to 28.7 mg, C/m(2)/day with maximum and minimum during summer and monsoon respectively. It was understood from the study, ammonia could be acting as the limiting nutrient for phytoplankton growth, while the role of nitrate, nitrite, phosphate and silicate remained insignificant. At the time of diatom population proliferates there was a drop in the nutrient levels was observed during the study. The water current flowing from north to south during the northeast monsoon, nutrient rich fresh water discharged from Tamirabarani River influencing the nutrient dynamics in the fishing grounds that are ultimately increasing the nutrients concentration during northeast monsoon.