To counteract human impacts and maintain the integrity of coral reefs, thousands of marine protected areas (MPAs) have been created around the world. But according to a new Nature Communications study, most of the evolutionary diversity of corals and fish aren't supported by this network of protected areas.
Evolutionary diversity is a measure of the differences in the length of the branches of evolutionary trees after species diversification. The total number of different species in an ecosystem is often a sign of how healthy it is, but understanding how related these species are (in evolutionary terms) is also vital since closely related species typically perform similar roles. More distinct lineages, on the other hand, have different or complementary roles that are critical for ecosystems to function. For marine environments, fossil records have shown that the extinction risk of species is mostly determined by geographic range size: Restricted range species are less buffered against variability under constantly changing environments.
So, to quantify the extent that evolutionary history is protected in coral reefs across the globe, a team led by David Mouillot of Université de Montpellier calculated how much of the geographic range of over a thousand species is covered by the MPA network. They focused on 805 species of coral and 452 species of fish from the wrasse family – two important parts of marine biodiversity with well-known evolutionary histories – who live in shallow reef habitats that have a monthly sea surface temperature of at least 17°C (62.6°F). Then, they looked at how much evolutionary history is encompassed by all the species on a shared evolutionary tree branch relative to this geographic range.
They found that, while the world’s MPA network currently covers 5.9 percent of the total coral reef area, it captures just 1.7 percent of the total known evolutionary history of corals, and only 17.6 percent of the evolutionary history of fish is protected. That means about 7,160 million years of the evolutionary history of corals and 3,586 million years of fish are not adequately protected by MPAs.
Marine protected areas were established at first to conserve species diversity, rather than evolutionary diversity. However, according to the researchers, the latter is a crucial – and often overlooked – component of biodiversity. It insures the long-term functioning of ecosystems by providing different ways of using resources or responding to disturbances, Mouillot explains to IFLScience.
For corals, the longest evolutionary branches with low protection are mostly in the Atlantic and the Eastern Pacific; for fishes, the highest concentrations of poorly protected long branches are located in the Western Indian Ocean and Central Pacific.
Butterflyfish and coral staghorn. Terry Hughes