Jimly C. Jacob, Ramya K. D, Bright Singh I. S and Rosamma Philip
Bathymetric and spatial alterations of sedimentary parameters and its influence on heterotrophic bacterial population in the shelf sediments of south east coast of India (Bay of Bengal) were analysed. The hydrographical parameters did not show significant (p<0.05) spatial variation though it varied with depth. Sediment was fine sand at 50 -100m depth and clayey silt at 200m depth. Organic matter in the sediment ranged from 0.95 - 3.76% showing significant depth wise variation (p<0.05). Total heterotrophic bacterial population ranged from 4.87 × 103 – 2.32 × 105 CFU g-1 dry wt. and the abundance was greater towards the northern latitudes. Bacillus, Vibrio and Alteromonas were the dominant genera in the shelf sediments followed by Alcaligenes, Enterobacteriaceae, Acinetobacter, Flexibacter and Moraxella. Significant positive correlation of bacterial abundance with sediment texture and organic matter was evident from the spearman rank correlation analysis. BIOENV identified dissolved oxygen, clay, silt and total nitrogen as a combination of environmental parameters that best explained the distribution patterns of heterotrophic bacteria (ρ = 0.644). The Principal component Analysis (PCA) displayed higher similarity of environmental characteristics within respective depth regions. First two components together explain 90% of the data variance between stations. The canonical correspondence analysis (CCA) further substantiated that major environmental parameters (such as temperature, dissolved oxygen, silt, sand and organic matter), had significant effects on the spatial distribution of culturable heterotrophic bacteria in the shelf sediments of Bay of Bengal.