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 × 104 to 6.34 × 104 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/m3 with high concentrates were recorded during summer. Primary productivity was ranged from 13.8 to 28.7 mg, C/m2/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.

The present investigation was intended to assess the seawater quality of Digha (India) in the northwestern coast of the Bay of Bengal. Digha is a meso-tidal coastal plain located between two major estuarine systems, i.e. Subarnarekha and Hooghly located respectively on the western and eastern sides of the West Bengal along the northeast coast of India. The sampling was made at nine stations at various distances. Significant seasonal variations in environmental parameters and nutrients were observed during the study period. Analyses of physicochemical characteristics of the study area indicated that the level of dissolved oxygen (DO), biological oxygen demand (BOD), total dissolved solid (TDS) and nutrients is within the permissible limit. The results clearly revealed that, though sewage discharge takes place in the coastal waters, the quality of the water was not affected. It may be due to the large quantity of estuarine water input from the Hooghly estuarine system that have enhanced dilution of discharged sewage in Digha coastal waters. Strong tidal activities, wave dynamics and coastal current further dilute the effluent water in the study area, resulting to the minimised sewage effect on coastal ecosystem. Further studies on the heavy metal concentration and benthic diversity can be assessed to understand the health of the ecosystem.

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