Distribution of size-fractionated phytoplankton biomass from the anthropogenically stressed tropical creek (Thane creek, India)

Abstract

Size-based partitioning of phytoplankton biomass is a crucial determinant of the type of food web functioning in an aquatic ecosystem. Seasonal and spatial distribution of total as well as size-fractionated phytoplankton biomass (pico, nano and micro-phytoplankton) from the tropical creek (Thane creek, India), was assessed in response to ambient physicochemical parameters. Nanophytoplankton biomass contributed the significant fraction (69%-97%) of total phytoplankton biomass throughout the creek irrespective of the seasons. The ability of nanophytoplankton to proliferate under low solar insolation helped them in sustaining high biomass in nutrient-rich turbid water. Microphytoplankton, which was the second dominant class, contributed 3%-19% during pre-monsoon, 11%-19% during monsoon and 3%-7% during post-monsoon. High suspended sediment load and mesozooplankton grazing pressure have played an essential role in structuring the microphytoplankton biomass. Competitive disadvantage under high nutrient concentration resulted in low picophytoplankton biomass throughout the creek. The dominance of nanophytoplankton biomass deciphered the prevalence of herbivorous based food web in the Thane creek. The Pearson�s correlation and the canonical correspondence analysis interpreted nutrient enrichment, suspended sediments and temperature played a significant role in determining the size structure of phytoplankton biomass. The eutrophication status of the study area studied using Trophic state index (TRIX). Availability of surplus nutrient during all the seasons could be the main factor behind the eutrophic to hypereutrophic (6.7-8.8) condition of the Thane creek.