Turning Brackish: Salinity-Driven Mangrove and Fisheries Decline in the Bangladesh Sundarbans.

The Bangladesh Sundarbans Reserved Forest covers about 6,017 km², forming roughly 60% of the world’s largest contiguous mangrove ecosystem, sustaining 2.7 million people. Since 1991, the reserve has lost 442 km² of forest cover, accompanied by a roughly 54% decline in recorded fish species richness at Mongla fish market (from 172 species in 2003 to 79 in 2016) and accelerating salinity intrusion across critical freshwater zones. The objective is to quantify the causal relationship between reduced freshwater inflow, accelerated salinity intrusion, and ecosystem service degradation in the Bangladesh Sundarbans, with a specific focus on mangrove species composition shifts and livelihood impacts. Methods include secondary data synthesis integrating hydrological records (1996-2020), forest cover mapping (2000-2020), fisheries statistics (Mongla market catch data, 2003-2016), climate impact projections across 27 scenarios to 2050, and ecosystem service valuations. Data sources include Bangladesh Forest Department biodiversity inventories, World Bank hydrological assessments, and peer-reviewed ecosystem studies. Key findings are that reduced Ganges freshwater inflow, primarily due to upstream abstraction and regulation, has intensified salinity penetration into the Bangladesh Sundarbans, exceeding physiological tolerance thresholds for high-value Heritiera fomes (Sundri) across 40% of the reserve. Species composition is shifting unfavorably: projected Sundri losses under all climate scenarios, while salt-tolerant but lower-value Excoecaria agallocha expands. Livelihood impacts are severe: Sundarbans-fringe upazilas, forest and estuary-based activities typically provide roughly 40-75% of household income, and malnutrition in dependent communities exceeds WHO thresholds. The Bangladesh Sundarbans are being damaged by climate change, local overuse, and above all, too little freshwater coming from upstream in the Ganges. Long‑term resilience of the Bangladesh Sundarbans requires institutional reform of Ganges water‑sharing as a prerequisite for effective biodiversity conservation and livelihood security.