The park occurs on the largest four islands (Tutuila, Ta'u, Ofu, and Olosega), of seven comprising American Samoa. All are rich in fringing coral reefs. The reefs typically have a shallow lagoon or moat (about 2 m deep), a shallower fore-reef, a reef crest (usually emergent at low tide), surge zone (with spur and groove formation on the south-west windward side) and a sharp reef front dropping 5-10 m to a reef terrace and gradually descending to deep water. The waters are clear and warm with abundant fish and have a great coral diversity. Over 200 coral species occur in the park, representing over half of all coral species found throughout the Indo-Pacific region. Dominant genera are Montipora and Porites , followed by Pavona , Pocillopora , Psammocora and Acropora .