Seasonal dynamics of body size in calanoid copepods (Calanoida: Copepoda) from the stressed tropical coast of India, Chennai, Bay of Bengal

Calanoid copepods have gained significant interest due to their rapid response to changes in environment. This study examined the seasonal variation in the size of calanoid copepods and their relationships to various environmental parameters in a tropical coast of India. Zooplankton samples were collected at Marina Beach, India, from January to December 2021. Ten calanoid species were selected based on their distribution to study the seasonal variation in the size, and the results showed a clear seasonal pattern, with smaller size of calanoid observed during summer months with high temperatures and larger sizes during the monsoon season associated with increased rainfall and nutrient availability. Negative correlations were observed between copepod size variation and temperature, while positive correlations were observed with dissolved oxygen, pH, salinity, and chlorophyll-a concentration. Acrocalanus gibber, Acrocalanus gracilis and Canthocalanus pauper showed changes that are more pronounced in body size (0.89–0.99, 1.12–1.23 mm and 1.41–1.52 mm, respectively) indicating species-specific responses to environmental fluctuations. These findings highlight the influence of environmental parameters in determining the size of calanoid copepods in tropical oceans. Moreover, this study contributes to our understanding of the ecological processes and global warming that determine copepod size variation in coastal ecosystems.