The distribution and diversity of culturable aerobic heterotrophic benthic bacteria in the continental slope of the Bay of Bengal: Linked abiotic factors, including a tsunami

The culturable aerobic heterotrophic benthic bacterial population and community structure in relation to the physico-chemical parameters in the continental slope of the Bay of Bengal was studied. In addition, diversity indices were calculated and pretsunami (in 2004) and post-tsunami (in 2005) diversity values were compared. Sediment samples were collected from two cruises in the depth zone of 214–1000 m (10°36′ N–20°01′ N and 79°59′ E–87°30′ E). The vertical distribution of the total heterotrophic bacterial population during both cruises was higher in the top section (0–3 cm) of the sediment. The average total heterotrophic bacterial population was in the range of 0.42–37.38 × 10⁴ CFU/g to 1.66–19.73 × 10⁴ CFU/g dry sediment weight during the two cruises, respectively. The limiting physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, and clay as revealed from multiple regression (r = 0.75) and BIOENV (Partial Correlation ρω = 0.447) analyses. The shannon-Wiener index (H′ log e), Simpson index (D), Margalef index (d) and Pielou’s evenness index (J′) were found to be higher in the 1000 m depth stations. Cluster analysis showed that the 500 m depth stations clustered either with the 200 m or with the 1000 m stations. The 200 m depth stations never formed a cluster with the 1000 m stations. Pre-tsunami diversity indices at two depth ranges (200 m and 1000 m) were higher than those of the post-tsunami indices, which was quite evident from the cluster analysis as well. This study confirms the effect of the tsunami surge in the sediments of the continental slope of the Bay of Bengal in the marine ecosystem, which is also attributed to the temporal variation of the heterotrophic bacterial population and diversity.