Coastal ecosystem services in South Africa’s largest natural bay: The role of marine benthic filter feeders in mitigating pollution

•We evaluated the role of mussels in enhancing coastal water quality.•The study took place in False Bay, Southern Africa’s largest natural bay.•Most environmental indicators showed a 2-way gradient: onshore-offshore, west-east.•Pollution inputs were mainly detected on one side of the bay.•Coastal circulation and intertidal filter feeders mitigated anthropogenic inputs.