Copepod community in the coastal waters off Kochi (India) signify the enhanced estuarine flushing during the Southwest Monsoon

Even though many studies refer to copepods as potential indicators of hydrographical settings and/or water masses, focused studies on this aspect are very scarce in Indian waters. Hence, this study assesses the hydrography and the copepod composition in a cross-shore transect (7–30 m depth zone) off Kochi along the southwest coast of India during different seasons to understand how seasonal hydrography alters the composition of copepods. The copepod community in the study area was found to consist of 36 species (26 dominant) during the Southwest Monsoon [(SWM) June to September], 31 species (16 dominant) during the Northeast Monsoon [(NEM) November to February], and 39 species (26 dominant) during the Pre-Monsoon [(PRM) March to May]. The salient observations in this study are (a) a higher contribution of cyclopoids (45–50%) during the oligotrophic PRM when the microbial food web was dominant; (b) the dominance of several truly estuarine copepods (Acartia plumosa, Acartiella keralensis, Pseudodiaptomous annandalei, and P. serricaudatus) during the SWM when the flushing of the adjacent estuarine system (Kochi backwaters) was the seasonal highest; and (c) the dominant occurrence of Temora turbinata, commonly referred to as an indicator of coastal upwelling, during both the SWM and the NEM indicates their conducive conditions in the study area during both seasons and (d) the occurrence of copepods Acartia danae, A. erythraea, Acrocalanus gibber, A. gracilis, Centropages orsinii, C. tenuiremis, Corycaeus catus, C. speciosus, Oithona similis, O. spinirostris, Oncaea venusta, Paracalanus parvus, and Undinula vulgaris in the study area regardless of seasons. The study concludes that, while the presence of truly estuarine copepods in the study area can be attributed to estuarine watermass indicators, the presence of several other dominant species found regardless of the season cannot, as their occurrence is widespread in the eastern Arabian Sea and the western Bay of Bengal, owing to seasonal water mass exchange between the two regions.