Unveiling the ecology of planktonic harpacticoids (Harpacticoida: Copepoda) in a stressed tropical coastal ecosystem, Bay of Bengal, India

The ecological role of planktonic harpacticoid copepods within marine ecosystems remains understudied. While primarily benthic, a subset of these organisms exhibits pelagic lifestyles. This research investigates the relationship between environmental factors and planktonic harpacticoid communities at Marina Beach, Chennai, a coastal area impacted by pollution from the Adyar and Cooum rivers. Zooplankton samples and environmental data were collected monthly from January to December 2021. Among the seven observed harpacticoid species, Longipedia weberi and Euterpina acutifrons displayed dominance, with mean abundances of 178.2 ± 190.54 ind./m³ and 196.5 ± 155.8 ind./m³, respectively. Notably, the distributional pattern of L. weberi differed from that of E. acutiforns, with the former prevailing when micro-nutrient content in the water was high, particularly from June onwards. Regression analyses revealed a positive correlation between L. weberi abundance and nitrite and phosphate concentrations (R = 0.31 and 0.358, respectively). Furthermore, redundancy analysis indicated a close association between L. weberi and other nutrient parameters, suggesting its potential as an indicator species for coastal eutrophication along the Chennai coast. Throughout the study period, the diversity and distribution of harpacticoid copepods exhibited variations across different months.