Abstract
Phytoplankton are the primary producer of the food chain in any aquatic ecosystem, and play a crucial role in maintaining fishery resources. The community structure of phytoplankton in tropical mangrove estuarine and adjacent coastal waters was investigated in the South China Sea from January 2013 to December 2013 to compare the significance of two water bodies. Study revealed, 102 species of phytoplankton species under 43 genera covering 6 species of Cyanophyceae, 4 species of Chlorophyceae, 63 species of Bacillariophyceae and 29 species of Dinophyceae from estuarine mangrove area. Whereas 67 species from coastal waters were recorded which comprised of 47 species of Bacillariophyceae, 16 species of Dinophyceae, 2 species of Cyanophyceae with 1 species of both the Dictyochophyceae and Chrysophyceae. The phytoplankton community structure and mean abundance (cells/L) were recorded in a systematic order of Bacillariophyceae > Dinophyceae > Cyanophyceae > Chlorophyceae in mangrove waters. While from coastal waters the systematic order was found as Bacillariophyceae > Dinophyceae > Cyanophyceae > Dictyochophyceae > Chrysophyceae. Phytoplankton mean abundance fluctuated from 567 to 88,890 cells/L in different seasons over the study period with its higher value in the dry season. The mean phytoplankton cell abundance in mangrove estuarine area (38,313.74 +/- 5614.26) found significantly (p < 0.0001) higher than the coastal water (1964.33 +/- 666.68). Phytoplankton species observed from the estuarine waters were dominated by Pleurosigma normanii, Coscinodiscus sp., Coscinodiscus centralis, Coscinodiscus granii, Dinophysis caudata, Ceratium carriense, Ceratium fusus, and Ceratium lineatum. While the blue green algae, Chaetoceros pseudocurvisetus, and Thalassionema sp. found most dominant in the coastal waters. Significant differences (R = 0.23-1, p < 0.05) were noticed in the phytoplankton species community assemblage between intermediate and wet seasons. The findings suggest that mangrove estuarine waters in South China Sea region were more productive in terms of phytoplankton abundance and diversity than coastal waters, which are influenced by the season.