Climate change leads to dead zones in Bay of Bengal, says study

Kochi: A new study that highlights the seasonality and the impact of climate change recorded the occurrence of a dead zone at the bottom, an area devoid of fish and other macro-organisms, in the western Bay of Bengal.

The study by scientists of the Centre for Marine Living Resources and Ecology (CMLRE), Union ministry of earth sciences, recorded the extreme dominance of a single species (Parascombrops pellucidus), a ray-finned fish, in the dead zone periphery, in a condition termed the ‘edge effect’. An edge effect is when a species lives on the boundary of two different habitats.

A dead zone is associated with the co-occurrence of cold and warm core air and strong biological pumping. According to the study, the continental margin of the western Bay of Bengal in the north is observed with a hypoxic area devoid of fish, termed a dead zone. The deep bottom realm is influenced by environmental changes indicating seasonality in the demersal communities. “There could be dead zones in the Arabian Sea also, but we haven’t looked at the marine life and its impact,” said BR Smitha, who authored the paper with M Hashim and KV Anish Kumar.

To understand the impact on marine life in that region, a total of 59 trawl operations were made in the depth range of 200-1,100m, yielding between zero and 1,190kg of total catch, including fish, crustaceans and molluscs. Zero catch was recorded at eight sites, most of which were in the slope regions at 100-1,200m depth.

Hypoxia in marine ecosystems directly or indirectly affects fish population structure, community composition and ecosystem functioning. This may result in excess mortality or the emigration of organisms from the area, resulting in dead zones.

The authors said the dead zone’s seasonal occurrence indicates the influence of natural or anthropogenically induced climatic variability can even affect demersal/bottom-dwelling organisms. The study region is known for the enormous sediment runoff from the north, from the Ganges-Brahmaputra riverine systems and several other peninsular rivers, indicating the anthropogenic intervention.