Double jeopardy and global extinction risk in corals and reef fishes

Coral reefs are critically important ecosystems that support the food security and livelihoods of hundreds of millions of people in maritime tropical countries, yet they are increasingly threatened by overfishing, coastal pollution, climate change, and other anthropogenic impacts, leading to concerns that some species may be threatened with local or even global extinction [1, 2, 3, 4, 5, 6 and 7]. The concept of double jeopardy proposes that the risk of species extinction is elevated if species that are endemic (small range) are also scarce (low local abundance) [8]. Traditionally, marine macroecology has been founded on patterns of species richness and presence-absence data [9, 10 and 11], which provide no information on species abundances or on the prevalence of double jeopardy. Here we quantify the abundances of >400 species of corals and fishes along one of the world's major marine biodiversity gradients, from the Coral Triangle hotspot to French Polynesia, a distance of approximately 10,000 km. In contrast to classical terrestrial studies [12], we find that the abundance of these species bears no relationship to the size of their geographic ranges. Consequently, double jeopardy is uncommon because endemics are often locally abundant, and conversely many pandemics are rare. The Coral Triangle hotspot has more numerically rare species (both endemic and pandemic) but also encompasses more species with intermediate and higher abundances. We conclude that conservation efforts in the sea should focus less on extinction risk and more on maintaining and rebuilding key ecological functions that are highly vulnerable to human pressures, even if species can avoid extinction