Copepods are considered as indicators of ecological stresses of estuaries. Spatial-temporal changes of diversity, abundance, and dominance of the copepod community of India's Ganges River estuary were hypothesised to result from abiotic fluctuations, seasonal change and the COVID-19 lockdown which possibly affected the habitat. This hypothesis was studied by sampling the estuary on different occasions between February 2019 and October 2020. Salinity and pH showed significant temporal variability but not significant spatial variability. Water temperature showed no significant spatial-temporal variability. Salinity showed significant negative relationships with diversity and abundance of the copepod community. After the COVID-19 lockdown (between unlock phase 1 to 5), nutrient status of the estuary did not show significant temporal variation. The copepod community mostly comprised calanoids except for the cyclopoids Oithona spp. Relative abundances of Pseudodiaptomus binghami, Eucalanus crassus and Labidocera euchaeta declined but Paracalanus indicus , Acrocalanus gibber , Acrocalanus gracilis , Acartia spinicauda , Acartia sewelli and Oithona brevicornis increased after COVID-19 lockdown. Bestiolina similis was the most abundant copepod and along with Acartiella tortaniformis , Acartia spinicauda , Paracalanus parvus and O. brevicornis co-dominated the community on various occasions. Spatial ordination of the copepod community was not significant either in the pre- or post-lockdown period. Diversity and total abundance of the copepod community were affected neither by seasonal change nor by temporal variability of water temperature and pH. Temporal variability of species richness was significant only in the post-lockdown period. Pre- vs. post-lockdown comparisons of diversity indices and total abundance of the copepod community were not significant. Overall, copepods were not much affected by abiotic and seasonal changes, and the COVID-19 lockdown. That indicates their flexibility to habitat variability and less suitability as indicators of chronic ecological stresses of excessively large river-estuaries.
Does the copepod community of the Ganges River estuary of India indicate ecological stress?