The bloom-forming dinoflagellate, Protoperidinium divergenshas been linked with coastaleutrophication in tropical and subtropical regions. Moderate to intense harmful algal bloom of dinoflagellates Protoperidinium divergens (33,500 cells. mL-1) was observed during June 2012in Junglighat Bay of Port Blair in South Andaman. Bloom of Protoperidinium divergenswas observed for four days and declined afterwards due to heavy rainfall with low seawater temperature of 24 to 26°C. A total of 63 species and 33 genera were identified. In the present investigation, the following species of phytoplankton and zooplankton were found to be common; phytoplanktonsuch as Amphorasp., Bacteriastrumsp., Chaetocerossp., Coscinodiscussp., Rhizosoleniasp., Gonyaulaxsp., Protoperidinium sp., Pyrophacussp.and zooplankton such as Paracalanussp.,Euterpina sp., fish eggs, Copepod nauplii, Codonella sp. and Tintinnopsis sp. Hydrobiologicalparameters analyzed during and post-bloom showed dissolved oxygen in the range of 2.23 –4.46mg.L-1. Nutrients such as nitrate varied from 0.37-1.118μmol.L-1,nitritefrom 0.37-1.118 μmol.L-1, phosphate (0.10-0.289 μmol.L-1) and silicate (6.22-9.333 μmol.L-1). Anthropogenic activities increased eutrophication in JunglighatBay and led to nutrient enrichment in the watercolumn, although precipitation could also have favoured the outbreak of these dinoflagellates.
Periodic algal blooms of three diatom species such as Coscinodiscus centralis, Rhizosolenia alata andRhizosolenia imbricata were observedduringSeptember 2011, December 2011 and March 2012 in the coastal waters of South Andaman Sea at Junglighat bay area (11° 39 N and 92° 43 E). The blooms were intense, with Coscinodiscus at aconcentration of 89,000 cells mL-1(contributing 85 to 98% to the total phytoplanktonpopulation), Rhizosolenia alataat a concentration of 13,000 cellsmL-1(86-93%) and Rhizosolenia imbricata at aconcentration of 19,000 cells. mL-1(91-99%). Nutrients, most importantly nitrate and silicate have emerged as the key factors controlling phytoplankton growth in this area.
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