Bunaken National Park extends over an area of 890.65 km² of which only 3% is terrestrial, including Bunaken Island, as well as the islands of Manado Tua, Mantehage, Nain and Siladen.
The waters of Bunaken National Marine Park are up to 1,566 m deep in Manado Bay, with temperatures ranging between 27 to 29 °C. It has a high diversity of - corals, fish, echinoderms or sponges. Notably, 7 of the 8 species of giant clams that occur in the world, occur in Bunaken. It also claims to have seven times more genera of coral than Hawaii, and has more than 70% of all the known fish species of the Indo-Western Pacific.
Oceanic currents may explain, in part, why Bunaken National Marine Park has such a high level of biodiversity. Northeasternly currents generally sweep through the park but abundant counter currents and gyros related to lunar cycles are believed to be a trap for free swimming larvae. This is particularly true on the south side of the crescent-shaped Bunaken Island, lying in the heart of the park. A snorkeler or diver in the vicinity of Lekuan or Fukui may spot over 33 species of butterfly fish and numerous types of groupers, damsels, wrasses and gobies. The gobies, smallish fish with bulging eyes and modified fins that allow them to attach to hard surfaces, are the most diverse but least known group of fish in the park.
source : wikipedia
