The Tortugas Banks are coral reefs that developed on a foundation of Pleistocene karst limestone at depths of 20 to 40 m. The banks are extensive with low coral diversity, but high coral cover. The most conspicuous coral is Montastraea cavernosa, and black coral (Antipatharia) are common on the outer bank edges. The banks are also used by groupers and snappers that support a major fishery. The banks lie within the Florida Keys National Marine Sanctuary.