Factors determining variations in viral abundance and viral production in a tropical estuary influenced by monsoonal cycles

Abstract

Viruses are the most abundant, dynamic, and ubiquitous components in the marine and estuarine environments. They outnumber prokaryotes in their abundance by at least one order of magnitude, but their relationship varies across environments. The present study examined the environmental factors (temperature, salinity, inorganic nutrients, and host abundance) that influence abundance and distribution of viruses in a tropical monsoonal estuary (Cochin estuary — CE) in India. Water samples were collected daily for one year from two stations with different hydrological settings in the estuary. Virioplankton abundance (VA) fluctuated daily with no definite pattern, but synchronized with the variations in prokaryotic abundance. On a seasonal scale, the abundance of virus and prokaryotes were higher during the summer months (pre-monsoon period) compared to monsoon and post-monsoon. The temporal dynamics of virioplankton was influenced by prokaryotic abundance (PA), viral production (VP), temperature, salinity and nutrient concentrations. The viral to prokaryote ratio (VPR) ranged from 1–44. There were significant (p<0.001) temporal and spatial variations in VA, PA, VP and VPR. The non-parametric distance-based linear regression analysis indicated viable prokaryotic abundance as the most important predictor variable for viral abundance. Other determining factors such as salinity, phosphate, and nitrate might have an indirect influence on the viral pool by altering host dynamics either by decreasing susceptibility to infection or by modifying characteristics of viral proliferation. Elevated densities of virus and prokaryotes during pre-monsoon season suggested an active and important participation of viruses in the dynamics of the microbial communities in this estuary during dry pre-monsoon season.