Bacterial dynamics along the west coast of India during the non-monsoon and monsoon season

Abstract

The West Coast of India (WCI) is influenced largely by semi-annual changes in the wind pattern and monsoonal currents. This is reported to cause upwelling which increases the phytoplankton growth in this region during the summer monsoon and it is recorded to be one of the world's highest primary productivity. Increase in the phytoplankton productivity is known to influence the microbial activity which is one of the key biogeochemical processes of the marine ecosystem as it plays an important role in the biotransformation of organic matter. However, the changes in the bacterial community structure and their heterotrophic enzyme activity with increasing primary production are not clearly understood from this region. Hence in this study, the bacterial dynamics along the WCI at Goa, Mangalore and Trivandrum, were investigated from the continental shelf, slope and off-shore region during the non-monsoon and monsoon season. Seasonal changes in the bacterial parameters such as abundance, viable counts and radioactivity based in-situ primary and bacterial productivity were estimated, along with the physicochemical characteristics. Statistical analysis shows a significant (p < 0.05) correlation between primary and bacterial productivity. Significant seasonal variations could also be established for the physicochemical parameters such as dissolved oxygen, nitrate, nitrite and phosphate, fluorescence values representing the chlorophyll concentration, bacterial abundance, viable counts and productivity. Taxonomic diversity studies on the cultivable bacterial morphotypes have shown that Proteobacteria, Firmicutes and Actinobacteria were the major phyla found during both the non-monsoon and monsoon season and Bacteroidetes, was represented only in the non-monsoon season. The bacterial community structure at phylum, genus and operational taxonomic unit levels also changed with higher diversity in the monsoon season. However, the hydrolytic enzyme activity of the bacterial morphotypes was comparatively lower during the monsoon season probably due to the active primary production. Though this study has improved our understanding of the monsoonal influence on the bacterial dynamics along the WCI, further studies based on metagenomic and transcriptome analysis are required to get a better understanding of the role played by the bacterial community from this region.