Known and Unknown Biodiversity, Risk of Extinction and Conservation Strategy in the Sea

Abstract

The ocean supports more different major kinds of organisms (phyla, classes) than any other environment on Earth. These lineages represent unique legacies that have been evolving separately for half a billion years and are more likely to contain novel genetic and chemical material than more recently evolved groups. Despite its huge expanse, the sea contains only 15% of the world’s 1.9 million described species. Empirical studies and calculations based on the species-area curve indicate that global coastal environments, tropical coastal zones and coral reefs support about 219,000, 195,000, and 93,000 described species, respectively. The pinnacle of presently known marine biodiversity, coral reefs occupy about 0.2% of the world’s oceans but contain 34% of the described marine species. Several lines of evidence suggest that as many as 90% of the species in the sea remain undiscovered and unstudied. If reefs contain the same area-specific diversity as rain forests, then coral reefs contain at least a million total (known and unknown) species. Almost half a billion people, 8% of the world’s population, live within 100 km of a coral reef, and over half of global coral reefs are under severe (about 30%) or medium (about 30%) threat. Ecological disturbances such as overfishing, overpopulation and mass mortalities of grazers, coral bleaching, outbreaks of disease, and loss of live cover due to sedimentation and other stresses plague coral reefs on a global scale. Marine environments have been considered to be less vulnerable to extinction than terrestrial and freshwater habitats due to the pervasive view that all marine organisms have long-lived pelagic stages and wide geographic distributions. It is therefore often concluded that marine conservation efforts must be of a very large, multinational scale. The present research indicates that most marine and especially coral reef species are small, inhabit holes in the bottom, produce few offspring, occupy restricted geographic distributions, and are vulnerable to extinction. If 30% of global reef habitats are degraded beyond recovery in the next few decades, we stand to lose almost 10,000 described species and at least 80,000 total (known and unknown) species (using the most conservative figures for total species). Because a significant percentage of marine species occupy restricted geographic areas, however, establishment of small marine protected areas (targeting either high species richness; rare, endemic or unique species; or unique or ecologically important habitats) can be effective. Where possible, they should be established in spatial networks that protect the critical habitats of species with broad dispersal and wider geographic ranges as well. However, these smaller marine protected areas are faster and easier to establish and maintain than large multi-national protective regions. They should be pursued relentlessly. The need has never been greater.