Copepod communities and trophic guilds: Patterns of structuring in tropical coastal waters off Southwest India
Date
2026Author
Swetha, R. A.
Madhu, N.V.
Praveena, S.
Muraleedharan, K.R.
Mohammed,H.S. E.
Jithin P.E.
Arya,K.S.
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Monthly investigations conducted during 2020 - 2021 in the nearshore waters (NSW <30?m depth) off Cochin and the Cochin Estuary (CE), along the southwest coast of India, aimed to elucidate the dynamics of mesozooplankton (MZ) community, with particular emphasis on copepod assemblages. Despite their close geographical proximity, the two systems exhibited pronounced differences in hydrographic regimes and biological responses. The CE, a tropical microtidal estuary, shaped by diurnal tidal oscillations and monsoonal river discharge, exhibited highly dynamic hydrography, while the NSW remained relatively stable although under the influence of seasonally occurring coastal upwelling, freshwater influx, and large-scale circulation in the eastern Arabian Sea. These contrasting forcings were reflected in phytoplankton growth patterns, with the CE sustaining higher but more variable chlorophyll a concentrations (6.16?�?5.22?mg?m?3) compared to the NSW (1.29?�?1.14?mg?m?3). Correspondingly, MZ biomass and abundance in the CE showed strong temporal variability, including a marked decline during the summer monsoon (SM) driven by freshwater influx, stratification, and salinity dilution. Copepods consistently dominated both the MZ communities in both systems (80% of total MZ), emphasizing their ecological resilience and trophodynamic significance. Bestiolina similis was a persistent and characteristic copepod in the NSW, regardless of season, reflecting its affinity for euhaline conditions, but its abundance declined in the CE during the SM period, indicating an intolerance to mesohaline environments. In contrast, during winter monsoon (WM) and spring inter monsoon (SIM), both systems supported higher abundance of euhaline copepod taxa such as Canthocalanus pauper, Nannocalanus minor and Corycaeus catus. Feeding guild analysis further revealed a sustained predominance of herbivorous copepods, particularly B. similis and Acrocalanus spp., in both enviornments, closely coupled with phytoplankton availability. Omnivorous and carnivorous copepods appeared episodically, especially in the NSW, where their dynamics were largely modulated by transient hydrographic fluctuations and prey variability.
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