4.4.3. Nitrogen fixation
The abundance of nifH gene was reported to be high in copepods collected from the coastal waters of Denmark (Øresund) (mostly contributed byAcartia spp.) with Vibrio spp. as dominant members[16]. But, in the present study, the nifH gene was found to be high in the CAB of Pleuromamma spp (Figure S4). and one should note that this may be due to the high abundance of genusVibrio in the CAB of Pleuromamma spp. (Supplementary File -S2). Vibrio attached to the exoskeleton, and gut lining of copepods [61] use chitin as carbon and energy source was reported in the past [10]. Furthermore, copepods are reported to be a hotspot for nitrogen fixation at a rate of 12.9–71.9 μmol N dm−3 copepod biomass per day[16]. The abundance of nifH gene in the CAB ofPleuromamma spp. maybe due to the presence of genera likeSynechococcus, Prochlorococcus, Bradyrhizobium, Microcystis, andTrichodesmium (Supplementary File S2).