Phytoplankton assemblage and UV-protective compounds in the river Ganges

Abstract

Interactions between physico-chemical parameters such as pH, temperature, nitrate, phosphate, alkalinity, acidity, biological oxygen demand (BOD), chemical oxygen demand (COD) and solar ultraviolet radiation (UVR) strongly affect aquatic ecosystems. Due to fluctuations in several environmental factors including river water pollution and UVR, organisms are under constant threat. However, phytoplankton protects themselves from environmental extremes by adopting several defense strategies including synthesis of photoprotective compounds such as scytonemin and mycosporine-like amino acids (MAAs). We investigated the presence of scytonemin and MAAs in phytoplankton of some polluted sites of one of the holy rivers of the world, the Ganges at Varanasi, India. We observed phytoplankton assemblages and studied certain environmental parameters which could possibly affect phytoplankton diversity in the river. Phytoplankton consisted mainly of 49 taxa of 34 genera belonging to Bacillariophyceae, Chlorophyceae, Cyanophyceae, and Chrysophyceae. The members belonging to Bacillariophyceae and Chlorophyceae were the two dominant classes, which comprised up to 75% of the total phytoplankton. Photoprotective compounds were isolated and characterized from phytoplankton. Electrospray ionization-mass spectrometry (ESI-MS) analysis of MAAs showed the presence of shinorine, palythinol, mycosporine-glycine and palythine. A high concentration of scytonemin was also observed with an absorption maximum at 386 nm in the studied phytoplankton.