Copepods of a creek and an inter-tidal beach of Ganges estuary: Perspectives of Professor Amalesh Choudhury memorial field work at Sagar Island, India

Copepods of inter-tidal estuarine beaches are less studied so hardly compared with those of creeks where both the habitats are integral parts of a single river-estuary; the current research is an attempt towards that. In a tribute to the legendry estuarine biologist of India Professor Amalesh Choudhury, a memorial field work was conducted by the author seasonally between February 2021 and October 2022 at Chemaguri Creek and inter-tidal beach of Sagar Island where Ganges estuary meets Bay of Bengal, a place where Prof. Choudhury did many of scientific works. During the field the author sampled copepod assemblages and measured water quality of Chemaguri Creek and inter-tidal beach at the south of Sagar Island. For both the habitats salinity and water temperature varied significantly among seasons but total Phosphate did not. The total Nitrogen levels varied significant among seasons only in the inter-tidal beach. Calanoid copepods of Paracalanidae and Acartiidae families dominated both the habitats. Species richness and cumulative abundance of the copepod community were higher in the creek than the inter-tidal beach. Dissimilarity within the copepod community of two contrasting habitats were 30.54%, majorly contributed by cyclopoids and harpacticoids. Inter-tidal beach had more harpacticoids than creek which had more cyclopoids than the previous. Acartiella tortaniformis dominated creek whereas Acartia spinicauda dominated inter-tidal beach. The community was largely made of small to medium size copepods. Multivariate analysis suggested both the habitats of the Ganges estuary, have respective micro-habitats which play prominent roles in limiting the community structure than the seasonal changes.