Influence of oil and gas exploration activities on the macrobenthic community structure of the Krishna-Godavari basin (Ravva coast), Western Bay of Bengal

The influence of oil and gas exploration activities on the macrobenthic community of an offshore oil and gas drilling site was investigated along the Krishna-Godavari basin (KG), Western Bay of Bengal. In the oil well sites, the enrichment factor of most of the metals (Cu, Zn, Pb, Cr) showed relatively higher values (EF > 10), indicating their anthropogenic origin. The macrobenthic community exhibited a conspicuous reduction in biomass (av. 33.5%), density (av. 20.9%) and diversity (av. 6.7%) in and around the oil well platforms. Polychaetes abundance increased towards the oil well platforms and decreased away from the wells, whereas cumaceans dominated at the coastal stations. The lower density of Ampelisca sp. in the oil well platforms and higher density at the locations away from the oil wells indicates the adverse effects of exploration activities. Along with the environmental variables such as depth, sediment texture and composition, trace metal concentration also had a prominent influence on the macrobenthic fauna. The biotic indices (H' index and AMBI) exhibiting slightly disturbed condition at the oil well sites; and M-AMBI exhibiting moderate-good-high condition, reveals the distinct distribution pattern of benthic communities in the region. Slightly disturbed conditions at a distance of 1-1.5 km from the oil wells compared to the undisturbed conditions at regions 3-4 km away from the platforms reveals the impacts of oil and gas exploration activities on the benthic habitat quality.