The island is characterized by its gentle relief in the northern half of the island and a mountain range in the southern half composed of several phonolitic peaks with altitudes between 500 and 948 meters where there is a patch of primary rainforest. The difference in geomorphology and terrain between the two sides, results in differentiated bioclimatology, has influence in the distribution of major types of ecosystems of the island, such as lotic systems in the area of the massif and its valleys and lentic systems in the northern plains area.

The biosphere reserve is home to great biodiversity in terrestrial as well as in marine ecosystems, with high rates of endemism in many groups of organisms, especially vascular plants, molluscs, insects, birds, reptiles and bats. It is part of the biodiversity hotspot of tropical forests of West Africa, containing a wide range of plant communities and habitats of high international importance such as primary tropical forests, forest shade, palm trees and lowland riparian habitats.

Considering the importance that this area has for the reproduction of sea turtles, seabirds and cetaceans, as well as coral reefs, on the international scene, it’s an area of great interest for the conservation of global biological diversity.