The impact of detritivorous fishes on a mangrove estuarine system

Sundarban mangrove ecosystem in India is one of the largest detritus based ecosystem of the world and it supplies the detritus and nutrients to the ad jacent Hooghly-Matla estuarine complex. In this estuary a group of fish com pletely detritivorous in nature, belonging to the genus Mugil spp. is prese nt. This group of fish is expected to have important effects on the trophic dynamics of ecosystems, but exact nature of these effects is not known. In order to study the impact that detritivory by fish may have on the estuari ne food chain, we developed mathematical formulations. We run two models, o ne with phytoplankton, zooplankton, carnivorous fish, detritus and nutrient and without this group of fish and a second one after including this fish in the system. In our model this group of fish has no major impact on prima ry productions of the estuarine system but has extensive role in total fish production. Coexistence of detritivorous fish and carnivorous fish occurs within reasonable parameter range. We have tested different growth rates of phytoplankton, grazing rates and predation rates of zooplankton, detritivo rous fish and carnivorous fish for total system equilibrium. Carnivorous fi sh predation rate on detritivorous fish and detritivorous fish grazing rate on detritus are very important. Different foraging ratios are also tested in this study. Foraging preference of carnivorous fish on detritivorous fis h appears significant for the system equilibrium. (C) 2001 Elsevier Science B.V. All rights reserved.