Ecophysiological status of copepods in the oxygen minimum zone of Eastern Arabian Sea

Eutrophication of marine ecosystems is a global problem, particularly in a changing climate and the spreading of Oxygen Minimum Zones (OMZs). The eastern Arabian Sea has both seasonal and permanent/perennial OMZs, but our understanding of the fauna there is extremely poor. So, this study investigated the composition and physiological status (alive or dead) of zooplankton (copepods) in the two OMZs. The study was accomplished by employing a Multiple Plankton Net and vital staining method. Our results showed for the first time that the oxygen deficiency adversely impacted the physiological status of copepods in OMZs which was reflected as (a) a two-fold decrease in zooplankton in the more intense oceanic OMZ compared to the coastal OMZ, (b) a marked increase of dead copepods in both OMZs (50 to 60 %) compared to normoxic waters (35 %) observed in previous studies and (c) higher copepod carcasses (50-70 %) and lower copepods larvae in the intense oceanic OMZ.