Antonymous nature of freshwater phytoplankton in the tropical estuarine environments of Goa, southwest coast of India

Abstract

Estuaries are the most dynamic marine ecosystems serving as potential spawning and nursery grounds for an array of marine fishes and their life stages. Producer community explicitly represented by phytoplankton form essential inertia to propagate the food chain, however on the contrary also could be detrimental due to blooming events. The present study envisages studying the distribution of green algae (Chlorophyceae) and blue–green algae (Cyanophyceae) in two tropical estuaries, namely Chapora and Sal in Goa along the west coast of India. Water samples were collected during July–December, 2016, comprising both monsoon and non-monsoon season. A total of twenty-five species of Chlorophyceae and three species of Cyanophyceae were recorded from these estuaries. Among the two, the Chlorophyceae group was found to be dominant and diverse. These two groups of phytoplankton were strongly influenced by the season in both the estuaries. The Multi-dimensional scaling (MDS) plots revealed salinity as one of the crucial parameters in the composition and distribution of these freshwater groups. Based on Redundancy analysis (RDA) plots, it was noted that, in addition to salinity, other physicochemical parameters (DO, pH, and nitrate concentration) could also affect the distribution of these groups. Two toxic bloom-forming genera (Microcystis and Oscillatoria) belonging to the Cyanophyceae group were reported. It is imperative that such events would play a role in the proliferation of these toxic species in the higher trophic levels.