Diurnal variation of phytoplankton community in the coastal waters of South Andaman Island with special emphasis on bloom forming species

Abstract

Species composition, abundance and distribution of phytoplankton dynamics were studied from the coastal waters of South Andaman Islands during December 2015 to February 2016. Physico-chemical parameters and phytoplankton species composition were observed during the study. Environmental parameters such as surface water temperature - 33ºC (r=0.96; <em>p</em><0.001), air temperature (r=0.78; <em>p</em><0.01), salinity 37 psu (r=0.42; <em>p</em><0.1), pH 7.8 (r=0.34; <em>p</em><0.1), and dissolved oxygen (6.14mg L^-1) were recorded. A total of 82 species under 50 genera of phytoplanktons were recorded belonging to Bacillariophyceae, Dinophyceae, Cyanophyceae and Silicoflagellate groups. Diatoms were represented by 68 species belonging to 40 genera, Dinoflagellates were represented by 12 species belonging to 8 genera, and 1 species belonging to a genera Cyanophyceae and Silicoflagellate were observed. Among the diatoms, <em>Coscinodiscus centralis, Rhizosolenia alata, R. imbricata, </em><em>Bacteriastrum furcatum, Leptocylindrus danicus, Odentella sinensis, Pleurosigma </em>sp.<em>, Skeletonema costatum </em>and <em>Thalassionema nitzschioides</em> and among the dinoflagellates, <em>Ceratium furca, Prorocentrum micans, P. divergens</em> and <em>Pyrophacus</em> sp. were the most prevalent diatoms and dinoflagellates encountered in the samples. The population density fluctuated between in the range of 53-63034 cells.mL^-1. The highest population density was recorded in January at (St.1) Chatham bay due to the blooming of diatom <em>R. imbricata </em>(63000 cells.mL^-1), were observed. Moreover, increase in water temperature and salinity was also found to be an influencing co-factor that had contributed to the algal bloom.