<p>Sustainable use of biodiversity in the Sundarbans- the world’s largest mangrove forest shared between Bangladesh and Indiahas become increasingly complex due to rising climatic and livelihood pressures. There has been a general agreement that traditional ecological knowledge (TEK) is key to supporting ecosystem services (ES) and community resilience, yet it continues to be undervalued in management decisions. This study investigates how communities in Koyra and Sarankhola, near the Sundarbans in Bangladesh, use ES with TEK, and how TEK changes because of ecological shifts and governance. Based on interviews, focus group discussions, and field observations, this study investigates how TEK mediates ES use in a rapidly changing the social- ecological system of the Sundarbans ecosystem. According to the results, ecosystem services are declining, and TEK is weakening, creating a social-ecological trap. The elderly master harvesters continue to possess strong ecological literacy- demonstrated through their ability to interpret tides, winds, and species behaviors yet younger generations are becoming increasingly disengaged from forest-based activities. Despite this, a measure of resilience persists, sustained by informal networks of cooperation and enduring cultural ethics. Our findings emphasize that ensuring the sustainability of the Sundarbans requires more than ecological restoration alone; one vital step is that TEK must be integrated into co-management frameworks, policies, and educational initiatives to safeguard both natural ecosystems and the cultural systems that sustain the Sundarbans ecosystem and dependent livelihoods.</p>