Impact of the Diatom Asterionella glacialis (Castracane) Bloom on the Water Quality and Phytoplankton Community Structure in Coastal Waters of Gopalpur Sea, Bay of Bengal

摘要

Occurrence of mono-species bloom of the diatom Asterionella glacialis (Castracane) in the coastal waters of Gopalpur sea, north-western Bay of Bengal and its impact on the water quality and phytoplankton community structure is reported in this paper. The bloom period persisted for about two weeks, from third week of March to 4th April 2004. Population density of phytoplankton discerned manifold increase from 4.63 x 10~4 cells l~(-1) on 22nd February 2004 to 3.96 x 10~7 cells l~(-1) on 26th March 2004. An overwhelming dominance of Asterionella contributing about 99.5% of the total phytoplankton count was observed during peak bloom period. Chlorophyll-a contents also showed an exponential increase that rose to 237.5 mg m~(-3) during peak bloom period from its pre-bloom concentration of about 3.26 mg m~(-3). The stable hydrographic conditions coupled with increased nutrient concentrations have triggered the blooming of this diatom species. Termination of bloom occurred with the depletion of nitrate and silicate in the medium water. Phytoplankton community structure in terms of their species diversity, species richness and evenness showed distinct variations during the pre-bloom, bloom and post-bloom periods.