Actively growing reefs are mainly restricted to the west, or leeward coast where a gently sloping shelf extends about 300 m seaward to a depth of 10 m. Fringing reefs form on this, mainly around headlands, as narrow segments, semi-circles or curved strips. They are generally poorly developed, consisting of reef rock and coral debris covered with Lithothamnion and sparse colonial growths o f Porites porites, P. astreoides, Siderastrea siderea and Millepora alcicornis. At the edge of the shelf, the sea floor falls regularly to about 20 m depth into a narrow trough paralleling the shore. Seaward, a submerged but still slowly growing barrier reef, 12-20 m deep and up to 100 m wide, runs parallel to the coast, extending from north to south and possibly connecting with a barrier reef along the south coast. A second fossil submarine reefal ridge runs parallel with this on the seaward side at 65-70 m depth.