Productivity changes, morphological adjustments, and Carbon gene profiling of prokaryotic population within the Eastern Arabian Sea during the wane of South West Monsoon

Bacteria are key players in shaping the dynamics of marine ecosystems. This study specifically examines heterotrophic communities in the Eastern Arabian Sea (EAS) along the West Coast of India (WCI) during the Southwest monsoon. We hypothesize that heterotrophic productivity, bacterial biomass and community distribution varies from south to north of WCI-EAS. Measurements were made along the EAS from 4 transects – Kochi (L1-L3), Mangalore (L4-L6), Goa (L7-L9) and Mumbai (L10-L12); 9°N-21°N - during September, 2019. The water samples were analyzed for bacterial production (3H), prokaryotic abundance (epifluorescence) and bacterial biomass (SEM) as cell specific carbon density. Metagenomic analysis was carried out to understand the genetic and functional diversity of bacterial community using Oxford Nanopore sequencing platform. Taxonomic analysis identified Proteobacteria as the dominant phyla in all stations (47-56%) followed by Bacteroidetes (3-26%) in the coastal stations. In the deeper station Proteobacteria is followed by Candidatus Marinimicrobia (3-24%), whereas Actinobacteria (2-24%) and Cyanobacteria (0-13%) higher in offshore surface waters. KEGG pathway analysis showed that bacterial communities of L1 (0m) and L10 (0m) were functionally more active in terms of metabolism than the rest of the stations; the KEGG level two analysis confirms the same in the case of carbohydrate energy metabolism, amino acid metabolism, lipid metabolism, translation and transcription as well. Distinct Carbohydrate active enzymes (CAZy) gene profile was observed between coastal and offshore as well as between north and south. Conclusively, our findings underscore substantial disparities in carbon-associated genes, unraveling their profound implications for the biogeochemical intricacies within the WCI.