A multi-criteria based optimal niche analysis of seasonal productivity in the Bay of Bengal using MODIS data

Abstract

Despite receiving enormous riverine nutrient inputs, the Bay of Bengal (BoB) has a long-standing biogeochemical paradox of comparatively low open-ocean productivity. To understand its long-term trajectory, this study analyzes a consistent two-decade (2003–2022) satellite dataset of Sea Surface Temperature (SST) and Chlorophyll-a (Chl-a) from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua. Our analysis reveals a significant basin-wide warming trend of +0.019 °C/year and spatially heterogeneous changes in productivity, with a pronounced apparent increasing Chl-a trend in the northern coastal zone (>1 μg/m³/year) and a slight decline in open-ocean regions. In areas of nutrient-driven productivity, a weak but statistically significant negative correlation (Pearson's r = −0.204, p < 0.05) between SST and Chl-a anomalies confirms the role of upwelling. As a secondary objective, we developed and applied an exploratory seven-factor Multi-Criteria Evaluation (MCE) model to synthesize these biophysical drivers based on weighted overlay and identify potential productivity hotspots. The model integrates data on SST and Chl-a suitability, thermal and biological fronts, upwelling potential, habitat stability, and depth. The MCE framework successfully identified key productive zones, including persistent biological fronts along the northern coast, characterized by chlorophyll gradients exceeding 6 mg/m³/km, a threshold corresponding to the 90th percentile of all observed gradient values. Notably, with scores >0.7, the spring pre-monsoon period stood out as a time of widespread high productivity, casting doubt on traditional theories of basin-wide oligotrophy. This integrated approach provides a robust quantification of climate-driven trends and offers an exploratory framework for mapping productivity suitability zones, serving as an essential tool for ecosystem-based management in the BoB.