Changes of the copepod community of Ganges estuary following tropical cyclone Yass

Abstract

Tropical cyclones (TCs) are straining the lower food web of Indian estuaries but regular institutional monitoring of those changes is rare. For that the ‘Cyclone Ecology’ research program was established in February 2019 on the Muriganga stretch of the Ganges estuary. On 26 May 2021, a category-1 TC Yass disrupted the ‘Cyclone Ecology’ research program sites. A before-after impact assessment was conducted of the cyclone-mediated changes. Water and copepod samples were collected in the pre-Yass (November 2020 to March 2021) and the post-Yass (June 2021) periods. The aim was to assess changes in diversity and dominance of the copepod community following TC Yass. Post-Yass, estuary became polyhaline for a while losing its usual meso-haline characteristic. Species richness of the copepod community was higher during post-Yass than the pre-Yass period. During the pre-Yass, calanoid copepods Bestiolina similis, Paracalanus parvus and Acartiella tortaniformis co-dominated the community and Bestiolina similis was the most abundant species. Post-Yass abundances of the cyclopoid copepods were considerably higher than the pre-Yass. Further, Oithona brevicornis replaced Bestiolina similisas the most abundant species of the community. Spatial heterogeneity of the copepod community of the pre-Yass period temporarily lost in the post-Yass. Changed species richness, abundances, dominance and spatial heterogeneity of the copepod community even for a short-term may have consequences for the ecology of the lower food web of an estuary. Keeping United Nations Ocean Decade (2021-2030) as the baseline, a nation-wide cyclone impact monitoring and resilience plan of the lower food web of Indian estuaries is recommended.