People living in poverty depend directly on local ecosystems for food and income, yet the coastal dimension of this poverty–environment nexus remains poorly understood. We examine seagrass-associated fishing and household poverty using household socio-economic data from 156 Indo-Pacific communities, linked to estimates of seagrass-proximate populations. Fishing households were consistently poorer than non-fishers, and seagrass-dependent households earned ~23% less than other fishers. Complete seagrass dependence was concentrated among lower-income households, with each additional purchasing-power-adjusted dollar per day associated with a 5.5% lower likelihood of exclusive seagrass dependence. Scaled across the Indo-Pacific, these patterns suggest at least 18 million people in poverty may use seagrass meadows while fishing, including 6.5 million who depend on seagrass as their only fishing habitat. These results make visible a population of millions that depend on seagrass, underscoring the need for management that identifies dependents, protects legitimate access and addresses land-based threats that undermine livelihood security.