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The largest continental shelf Oxygen Minimum Zone (OMZ) in the world is formed along the Indian western shelf in the eastern Arabian Sea during the Southwest Monsoon [(SWM); June–September], which is a natural pollution event associated with the coastal upwelling. This study examines the composition, abundance, and distribution of copepods during the Northeast Monsoon [(NEM); November to February] and SWM in 50 m depth zones along the Indian western shelf in the eastern Arabian Sea. The NEM was characterised by warm, stratified, and low-salinity waters in the southeast Arabian Sea and cold, high-salinity, and well-mixed waters in the northeastern Arabian Sea. During the SWM, cold and Dissolved Oxygen (DO) deficient waters (<22 μM/0.5 ml L−1), which are the signs of coastal upwelling, were evident all along the study zone, but with more intensity off Kochi, Mangalore, and Goa in the south than off Mumbai and Okha in the north. The zooplankton total biomass and abundance showed seasonality with a general decrease during the SWM (av. 3.68 ± 1.29 ml m−3 and av. 5711 ± 3096 Ind. m−3, respectively) compared to the NEM (av. 7.37 ± 2.17 ml m−3 and av. 14,473 ± 4966 Ind. m−3, respectively). At the same time, the abundance of Polychaeta and Siphonophora showed an increase during the SWM (av. 1187 ± 1055 Ind. m−3 and av. 169 ± 119 Ind. m−3, respectively), probably a result of the DO deficient waters associated with upwelling. Two striking seasonal features in Copepoda community were evident in this study: (a) a compositional shift from Cyclopoida dominant during the NEM to Calanoida dominant during the SWM, and (b) the coastal OMZ along the Indian western shelf during the SWM was dominated by Calanoida, which include oceanic OMZ species such as Pleuromamma indica , Lucicutia flavicornis , L.paraclausii , Eucalanus elongatus , Subeucalanus pileatus , S.subcrassus , and Clausocalanus furcatus. This forms a clear imprint for the extension of the oceanic OMZ into nearshore waters during the SWM due to coastal upwelling. • Considered Copepoda as an indicator of coastal hypoxia along the Indian western shelf. • A compositional shift of Copepoda was evident during different seasons. • Many Copepoda of oceanic OMZ were found in the coastal hypoxic zones. • The study shows the biological continuity of the coastal and oceanic OMZ. [ABSTRACT FROM AUTHOR]

The baseline study of Microplastics (MPs) in zooplankton (copepods, chaetognaths, decapods, and fish larvae) from six different zones along India's west coast (off Kanyakumari/Cape Comorin, Kochi, Mangalore, Goa, Mumbai, and Okha) in the Eastern Arabian Sea (EAS) is presented here with their vast ecosystem impacts. This investigation revealed that zooplankton in all six zones accumulated MPs pellets (52.14%), fibres (28.40%), films (10.51%), and fragments (8.95%). The highest average retention of MPs (MPs/individual) was found in fish larvae (av. 0.57 ± 0.18) while copepods had the lowest (av. 0.03 ± 0.01). The presence of low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate was confirmed by Raman Spectra of MPs. The MPs in zooplankton found in this study (av. 22 ± 7 pieces/m3) were nearly 2-fold greater than those found in some of the world's most densely populated areas. It is shown that the strong southerly coastal currents could advect the MPs contaminated water mass too far away, having the potential to affect the fish and corals. • This pilot study on Microplastics (MPs) was focused on the west coast of India. • MP contamination in selected marine zooplankton groups is being investigated. • Out of four kinds of MPs found, the pellet type was the dominant one. • MPs increased at higher trophic levels within the zooplankton community. • High MPs in zooplankton and the coastal currents aggravate the risk of transferring them to fishes and corals. [ABSTRACT FROM AUTHOR]