Comparative VGP models to analyse the primary productivity in the north Indian ocean and the linkages with rising sea surface temperature

The Primary Productivity of an ecosystem is an indicator of the health of the marine ecosystem and fishing yield. Primary productivity across the continental sea of the North Indian Ocean (NIO) basin was estimated using two vertically generalised production models. We examine the productivity using two non-parametric tests and present the changes using a gridded basin map. In the Behrenfeld and Falkowski (BF) approach, estimated primary productivity shows a significant decline of over 6550 km² from 2003 to 2020, recorded spatially 100 km² adjacent to the coastline. However, an area of 825 km² across the exclusive economic zone of the Indian sub-continent has seen a significant rise in primary productivity. The Kameda and Ishizaka (KI) model limits productivity reduction to 2500 km² across the NIO basin. The seasonal trends indicate reduced summer productivity across the basin. Both models point towards a significant reduction of productivity observed across the Bay of Bengal (BoB) and Arabian Sea (ARS) coastal regions owing to the damaging effects of anthropogenic-induced global warming. Secondly, simultaneous regression analysis using climate-based indicators and satellite-based NPP and Chlr-a data shows a significant reduction with high magnitude in the levels of NPP across the BoB and ARS between 1997 and 2020 due to rising sea surface temperature and a reduction of 9% and 6% in chlorophyll-a levels, respectively. These results point towards the inverse linkage between the rising SST on the primary productivity of the NIO basin and its devastating impacts on marine fisheries, especially in the BoB. These findings underscore the need for urgent action to mitigate the impacts of climate change and promote sustainable management of marine resources.