The lowered biomasses and fragmented habitats resulting from the impacts of fishing are predicted to lead to local extinctions especially among large, long-lived, slow growing species. Key ecosystems are those ecosystems for which it is most important to measure changes in extent, or those ecosystems for which it is possible to measure changes in extent. In many countries, coral reefs contain rare or locally endemic or threatened species, are of particularly high species richness, represent rare or unusual habitat, are severely reduced in area relative to their potential original extent, are under a high degree of threat, and/or are of high actual or potential economic importance.