Ecosystem modelling to understand the trophic dynamics and ecosystem health of a small tropical Indian estuary

Abstract

Estuaries provide enumerable ecosystem services to mankind in terms of provisional, regulating, supporting, recreational and information services. However, the persistent human-environment interactions for these services altered the ecological integrity of estuaries. Although the small estuaries receive little attraction in scientific studies due to their low surface area and regional importance, these ecosystems are more vulnerable to anthropogenic pressures and require urgent attention from the scientific fraternity. The Terekhol Estuary (TRE) is a small tropical estuary situated along Goa, west coast of India, gaining recognition in recent years due to the pollution risk from tourism activities. Moreover, the estuary also behaves as an extension of the marine realm during the dry season. The food web structure and network flow indices of the TRE was assessed to reveal its present ecological status. The Ecopath modelling approach was employed to delineate the ecosystem structure and trophic functioning of the estuary distributed in 22 ecological compartments from 2018 to 2019. The trophic level of the food web ranged from detritus (TL-1) to sharks (TL- 4.53). The ecosystem structure demonstrated a grazing chain (herbivory) based organization over the detritus-based pathway. The proportion of exports to the total flows was 35% for the TRE. The model has a high total system throughput (12,043.6 t km−2 year−1), low system omnivory index (0.17) and connectance index (0.21), and a moderate relative ascendency (45.1%). Finn's cycling index (2.17%) indicated very low recycling in the system. All these indicators along with the eco-exergy index (8567.22 g detritus equivalent m−2), specific eco-exergy (38.25) and robustness index (0.11) classified the estuary as be immature, less stable and less organized and is in the initial stages of its development. The ecological indicators analyzed here point towards a medium to a high level of impact in the TRE due to anthropogenic activities. We also highlight the management measures to be implemented in order to restore the ecological quality of the TRE.