Phytoplankton community structure along offshore transects of some Indian estuaries of east coast: An experience with a summer cruise

Abstract

This paper is based on the analyses of samples collected during a summer cruise onboard CRV ‘Sagar Paschimi’ (Cruise no.09/11) from 1^st to 8^th of April 2011. Species composition, abundance and distribution of phytoplankton, and water quality parameters (transparency, water temperature, salinity, pH, dissolved oxygen, nutrients <i>viz</i>. NO₂, PO₄ and chlorophyll-<i>a</i>) were examined in this study. A total of 123 phytoplankton species were identified. Of total, 86 species of diatoms from 44 genera, 22 species of dinoflagellates from 10 genera, 5 species of green algae from 5 genera, 4 species of cyanobacteria from 4 genera, 2 species of cocolithophores from 2 genera and 1 species of silicoflagellate were identified. Phytoplankton communities were found to vary from transect to transect. Highest and lowest values for species diversity index are associated with Godavari and Gosthani transects respectively. The highest phytoplankton abundance was found at transect Krishna (26680 cells/l) and the lowest at Godavari (9480 cells/l). <i>Thalassiothrix longissima</i> was quantified as the dominant species among diatoms and <i>Dinophysis caudata</i> among dinoflagellates. Abundance of bloom forming species <i>Asterionellopsis glacialis</i> was observed at transects Godavari & Mahanadi. Diversity and evenness indices of phytoplankton were found highest at Godavari transect. There exhibited a linear relationship between chlorophyll-<i>a</i> and phytoplankton abundance at all the transects with deviations at Gosthani and Godavari.