View article

Diverse anthropogenic activities including alteration of hydrological regime and agricultural development in the upstream of the river catchments modify the structural components of communities and ecological roles of species in estuarine ecosystems. The present study compared the diet, carbon (δ13C) and nitrogen (δ15N) isotope ratios and Layman community metrics of predatory fish and their prey-fish between two estuaries with different degrees of anthropogenic disturbances. The Layman community metrics were estimated following the Bayesian approach. It was revealed that the diets of the predators Arius africanus, Epinephelus coioides, Sillago sihama and Pomadasys argenteus, and their isotopic values including their main prey, the fish Valamugil buchanani, were significantly different between Wami and Pangani estuaries (PERMANOVA, Pseudo-F≥ 3.1, p= 0.05). The comparison test of isotopic niche width at estuary level showed that the isotopic niche of Wami estuary was slightly narrower (3.90-6.94 at 95% CI) than that of Pangani (5.70-9.69 of 95% CI). The comparison of the δ15N values and range of species between estuaries suggest shifts in trophic position of the species in Wami estuary relative to that of Pangani. Furthermore, the Layman metric indices of trophic diversity and redundancy of Wami estuary were substantially smaller, when compared to that of Pangani estuary. These findings indicate that, even though the Wami estuary stands under a conservation status, the extent of disturbances in the upstream is potentially high and enough to induce the ecological changes at the base of the food web downstream, giving rise …