This exceptionally vast zone has been divided into four sectors, each of which possesses unique characteristics.
In the North-West sector, the great sedimentary plains of the lagoon shelter significant populations of reef sharks, Malabar groupers, giant Harlequin sweetlips and manta rays.
The sector is also a refuge for seven species of marine snakes and comprises 75 % of the islets located in North Province waters. These islets are used as nesting grounds by most of the marine birds frequenting the area.
The North-East sector is a favourite gathering-place for dugongs and also boasts several green turtle nesting sites. Almost all of New Caledonia's mangrove species are found in the dense and widespread estuary mangroves and the vast seagrass beds serve as breeding areas and nurseries for a number of fish families (Gerreidae, Lethrinidae and Lutjanidae).
Two barrier reefs off the coast from Hienghène are an outstanding feature of the Eastern sector, which is bordered by 1,200 ha of wetlands fringed by mangroves. Corals of exceptional size dot the excellently well preserved seaward slopes of this sector. During the southern winter, the area offers humpback whales a safe and clement refuge, and is also a key nesting site for loggerhead turtles.
Finally, the South-East sector is one of New Caledonia's greatest treasures in terms of marine biodiversity. Some species rarely found elsewhere (Ribbon eels, Lacy scorpionfish and Humphead parrotfish) are almost a common sight here. Humpback whales also use the sector to breed and rear their calves and, in September and October, it is not unusual for sperm whales to draw near the outer reefs on their migration northwards.