BIOMASS AND SEASONAL VARIATION OF PLANKTON DIVERSITY IN SEAGRASS AND CORAL REEF ECOSYSTEMS OF MANDAPAM COAST IN GULF OF MANNAR
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Date
2017
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Fisheries College and Research Institute, Thoothukudi, Tamil Nadu Dr.J.Jayalalithaa Fisheries University
Abstract
The present study was conducted to assess the plankton species diversity, biomass and its seasonal variations in the three coastal locations in the near shore waters of Mandapam viz. Chinnapalam (station 1 – coastal water with seagrass beds), Shingle Island (station 2 - coastal water with coral reefs) and Kundhukal (station 3 - coastal waters without seagrass and coral reefs as control station). Monthly sampling was carried out from September 2016 to May 2017 in all the three stations. The overall minimum and maximum values of surface water temperature, depth, pH, salinity, dissolved oxygen, nutrients (nitrite, nitrate, phosphate and silicate), ammonia, BOD, COD, gross primary productivity and chlorophyll-a in all the three stations were between 25 and 30⁰C, 0.5 and 1.15 m, 7.68 and 8.23, 31 and 36 ppt, 2.68 and 4.69 ml. l-1, (0.0186 and 0.6318 μg-at-NO2-N.l-1, 0.0005 and 0.049 μg-at-NO3-N.l-1, 0.1123 and 1.1621μg-at- PO4-P.l-1, 0.084 and 1.981μg-at- Si.l-1), 0.0012 and 0.168 μg-at-NH3-N.l-1, 0.22 and 3.12 ml.l-1, 0.32 and 3.84 mg.l-1, 0.0737 and 1.194 mgC.m-3h-1 and 0.01 to 2.11 mg.m-3 respectively. All the water quality parameters were found to be within the levels prescribed for coastal waters. During the study period, a total of 69 species of phytoplankton and 65 species of zooplankton were recorded. Of these 60, 46 and 62 species of phytoplankton and 59, 49 and 59 species of zooplankton were observed in the stations 1, 2 and 3 respectively. The minimum and maximum number of phytoplankton ranged from 11 to 30, 10 to 18 and 12 to 29 at stations 1, 2 and 3 respectively. The minimum and maximum number of zooplankton ranged from 18 to 40, 16 to 23 and 19 and 36 at stations 1, 2 and 3 respectively. In station 1, the density of phytoplankton and zooplankton ranged between 89 and 1123 cells.l-1 and 126900 and 667400 nos.m-3 respectively. The density of phytoplankton and zooplankton ranged between 61 and 122 cells.l-1 and 108100 and 512300 nos.m-3 respectively in station 2, whereas the station 3 had the range of density of phytoplankton and zooplankton between 70 and 1081 cells.l-1 and 89300 and 935300 nos.m-3 respectively. The eggs of Caranx sp. were observed during January 2017 and February 2017 at station 1 and the same was observed during November 2016, January 2017, and April 2017 at station 3. The eggs of clupeid group were also observed during January 2017 at station 3. Few species of fish larvae were observed during March 2017 at station 1 and during February 2017 and May 2017 at station 3. The species richness index varied from 2.15 to 5.38, 1.88 and 3.43, and 2.27 to 4.90 at stations 1, 2 and 3 for phytoplankton respectively. For zooplankton it varied from 3.33 to 7.13, 2.97 to 4.30 and 3.64 to 6.29 for stations 1, 2 and 3 respectively. The species diversity index for phytoplankton and zooplankton varied from 0.43 to 1.20 and 0.88 to 1.58, 0.89 to 1.25 and 0.96 to 1.32 and 0.89 to 1.26 and 1.16 to 1.51 for stations 1, 2 and 3 respectively. Phytoplankton density showed a significant (at 5% level) positive correlation with nitrate and salinity in stations 1 and 3 respectively. Zooplankton showed significant (at 1% level) positive correlation with salinity and net primary productivity in station 2. The study concluded that the seagrass ecosystem is more productive with high plankton biomass and diversity than the coral reef ecosystem.
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