Ecosystem models are essential for understanding the complex trophic interactions of a marine food web. An Ecopath model was built on Northern Bay of Bengal (NBoB) ecosystem considering 29 functional groups to understand the trophic interactions and ecosystem functions. Results showed that the mean trophic level of the NBoB ecosystem was 3.146. The ecotrophic efficiency of the ecosystem ranged from 0.510 to 0.995. Species such as Arius spp., Tenualosa ilisha and Harpadon nehereus showed higher ecotrophic efficiencies which suggested that those species were highly exploited. The total system throughput was 4163.712 t/km2/year. Further, Finn's cycling index was 14.39% of the total ecosystem throughput and the Finn's mean path length was 3.203. The ratio of total primary production to total respiration was 1.445 and the total transfer efficiency of the NBoB ecosystem was 16.43%. Those statistics suggested that the NBoB is a highly efficient detritus-based ecosystem which is possibly in its early stage of maturity. The mixed trophic impact analysis showed that the majority of the functional groups had negatively affected the trophic interactions of the NBoB ecosystem but the detritus, phytoplankton, benthos and non-penaeid shrimps had positively affected the trophic interactions. Use of trawl and bag nets had considerable negative impacts on the various functional groups of the NBoB ecosystem. In the NBoB ecosystem elasmobranchs was the keystone group. Upeneus spp. and Polynemidae, and Caranx spp. and Carangidae had considerable niche overlaps in the NBoB ecosystem. Overall increases in the mean trophic level, Finn's cycling index, gross efficiency and fluctuations of the total biomass were the key indicators of the changes that the NBoB is experiencing in recent years. That may affect the trophic interactions of the NBoB foodweb; therefore, regular monitoring of the components of the food web is recommended.
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