Coral reefs occur in warm, clear, shallow ocean habitats that are rich in life. The reef’s massive structure is formed from coral polyps.Polyps are tiny animals that live in colonies; when coral polyps grow, they leave behind a hard, stony, branching structure made of limestone. Pillar Coral (Dendogyra cylindrical), sponges and soft corals such as Sea Fans (Gorgonia sp.), Sea Whip (Pterogorgia pp.) are abundant in St. Maarten’s waters.
Fringing reefs are the most common reef type around St. Maarten. Patch reefs (small isolated reef areas) are found along the eastern, western and southern coasts and can be observed at dive sites such as Isabella Reef, One Step Beyond and Little Sister. Many upper reef slopes on the eastern part of the island have spur and groove formations (coral ridges alternated by sand channels). These can be observed as dive sites such as Spanish Rock, Molly BeDay and Hen and Chick.
Coral reefs help protect the coastline from storm damage by reducing wave energy and slowing/diverting water currents. They also provide a safe shelter as well as feeding grounds for many marine animals such as fish, sponges, sea fans, shrimp, conch, lobsters, anemones, octopus, crabs, molluscs, urchins, worms and sea anemones. For some fish, such as parrotfish, the coral itself provides a source of food; others, such as sharks and barracudas live off the reef’s inhabitants and visitors.
A total of 153 species of reef fish have been recorded at St. Maarten’s dive sites; the most common are Blue Tang (Acanthurus coeruleus), Bluehead (Thalassoma bifasciatum), Sergeant Major (Abudefduf saxatilis), Spotted Goatfish (Pseudupeneus maculatus) and Ocean Surgeonfish (Acanthurus bahianus).
The most common shark species is the Blacktip Reef Shark (Carcharhinus melanopterus). Spotted Eagle Rays (Aetobatus narinari) are also present. All four Caribbean species of sea turtle can be found on St. Maarten’s reefs, cropping on soft corals and sponges: Hawksbills (Eretmochelys imbricate), Green Turtles (Chelonia mydas), Leatherbacks (Dermochelys coriacea) and Loggerheads (Caretta caretta). The latter are rare visitor.
While St. Maarten’s reefs are in good condition in comparison to other Caribbean reefs, they face a number of natural and man-made pressures. Unsustainable development on the island has resulted in the sedimentation and nutrient enrichment of the marine environment, which in turn smothers and kills reef organisms. The raised nutrient concentration from pollution stimulates the growth of algae, which can out compete hard corals for settlement space.
Natural threats include storm damage, outbreak of disease, coral bleaching agents.