Abstract
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.
Highlights
Phytoplankton diversity in the ocean may influence the functioning of marine ecosystems through overall productivity, nutrient cycling and carbon export (Goebel et al 2013)
The fluctuation in nutrient concentration was mainly due to influx of fresh water from Thamirabarani river and monsoon rainfall
Since water current flowing from north to south during the northeast monsoon, nutrient rich fresh water discharged from Thamirabarani River influencing the nutrient dynamics in the fishing grounds that are increasing the nutrients concentration during northeast monsoon
Summary
Phytoplankton diversity in the ocean may influence the functioning of marine ecosystems through overall productivity, nutrient cycling and carbon export (Goebel et al 2013). Variability in primary production may influence the fishery productivity and a strong link between phytoplankton and fisheries variability is proposed by Bainbridge and Mckay (1968) and Cushing (1975) All these factors in turn collectively support the fishery resources of coastal ecosystem. Any changes including depletion of nutrients and biological parameters would affect the health of the coastal ecosystem and alternatively reduce the fish productivity. Phytoplankton alone contributed to about 90.0 % of the total marine primary production (Satpathy et al 2010) The physical process such as hydrodynamic conditions and current patterns are influencing the primary productivity and determining the phytoplankton’s distribution (Dickie and Trites 1983). Chlorophyll ‘a’ (Chl-‘a’) is a unique parameter that influences the primary productivity of aquatic ecosystems and initiates the marine food chain. The hydrographic conditions along the east coast of India undergo significant changes with seasons
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