Fish communities reveal the ecological quality of a small, temporarily closed tropical estuary in response to natural and anthropogenic interventions

In this study, an estuarine fish community index (EFCI) was applied so as to evaluate the ecological quality of Poonthura estuary, a temporarily closed sandbar estuary, located along the south-west coast of India. Specifically, the study examined the impacts of several natural and anthropogenic interventions, (1) a pollution mitigation plan of the confluent rivers draining into the estuary, during the years 2016 and 2017, (2) extreme climatic events in the form of catastrophic floods during 2018–2019, and (3) closure of the largest solid waste disposal plant located near the banks of the rivers that drain the estuary followed by river cleaning and restoration initiatives during 2019–2020. The EFCI could thus be compared at two different time periods (2016–2017 and 2019–2020) to assess the ecological condition of PE. The EFCI was also applied to assess the ecological condition of PE during open, semi-closed, and closed-mouth state events. The estuary is rated as a moderately polluted system, since the threshold value (42) falls well below the maximum score of 100. The increased freshwater flow associated with flooding and the closure of the largest sewage treatment plant could have resulted in increased fish diversity and improvement in ecological quality during the years 2019–2020.