Evaluating energy flow, trophic structure, and network indices of a tropical reservoir ecosystem in Southern India

Abstract The foodweb of the Karapuzha reservoir ecosystem was constructed using modelling software Ecopath with Ecosim. This reservoir has a high biomass of primary producers that can support a fairly large fish biomass. Ecotrophic efficiency values of zoobenthos show that these primary consumers are heavily consumed. Hence at higher trophic levels flows are very low. The overall estimated fish biomass in the reservoir was 23.01 metric tonnes, with the carps having higher biomasses than other fish species. The trophic structure reveals that the reservoir can be split into four trophic levels. Flow from trophic levels I to II was 1123 t km−2 whereas flows from level II into level III was just 257.8 t km−2. Analysis of Lindeman's spine indicates that the foodweb of the Karapuzha reservoir is primarily a grazing food chain. The ascendancy of the Karapuzha reservoir is estimated at 24.5 percent, indicating a high overall maturity. This suggests that Karapuzha is immune to disturbance and a reasonably mature environment, although with a vulnerable foodweb. The large biomass of zooplankton and the TPP / TR value of 1.77 show that it is a healthy ecosystem but for overfishing, which is an area of concern. Stocking this reservoir with major carps (Catla catla, Labeo rohita and Cirrhinus mrigala) will help to properly use the primary production and also enhance energy flows. This will also help to improve the livelihood of the local tribal community who depend on fish catch from this reservoir.