If a new zoning system needs to be designed, the first step is to delineate the core zones, or
sanctuaries, that can tolerate only a minimum of human use. These are habitats that have high
conservation value and are vulnerable to disturbances. No disturbing uses should be allowed.
Core zones should be large; they should include as large a variety of habitats as possible, and be
large enough to sustain a breeding population of the key species. Small areas of habitat will have
fewer species than larger ones, and thus, a large core zone may be necessary to protect the
majority of species. For example, a 300-hectare coral reef of the Chagos Archipelago in the
Indian Ocean contained 95% of all the coral genera found in the archipelago, but smaller reefs, or
smaller sections of reef, had lower coral diversity. The number of coral genera decreased as reef
size decreased. Also, certain genera were found only on reefs larger than a certain minimum
area