Delineating the food web structure in an Indian estuary during tropical winter employing stable isotope signatures and mixing model.

Abstract

The food and feeding links and sources in an impacted tropical estuary situated along India's western coast, the Ulhas River Estuary (URE) was analyzed employing the stable carbon and nitrogen isotopic signatures (δ13C and δ15N). Three basal carbon sources, such as mangrove leaves, particulate organic matter (phytoplankton), and detritus, were analyzed together with eight consumer groups from various trophic guilds. The δ13C varied from - 19.67 to - 24.61‰, whereas δ15N ranged from 6.31 to 15.39‰ from the primary consumer to the top predator species. The stable isotope mixing model developed for URE revealed a phytoplankton based pelagic food chain and detritus based benthic food chain in URE. The fairly larger value of SEA (Standard Ellipse Area) in the URE suggest a much broader food web structure and high trophic diversity in the ecosystem. Higher influence of detritus on the assimilated diet of majority of consumers and evidences of nitrogen enrichment in the basal sources such as detritus and particulate organic matter by anthropogenic activities in URE point towards nitrogen pollution and subsequent trophic disturbance in this tropical estuarine ecosystem.