A future ocean that is too warm for corals might have half as many fish species

It is difficult to predict the possible effects of coral loss on fish communities worldwide, especially since reef fishes are a source of protein for millions. University of Helsinki has released a new study that predicts how fish biodiversity will react to decreases in coral diversity. It shows that coral loss could lead to a 40% drop in global reef fish diversity.Corals bleach more quickly and die more often when the water gets warmer. What happens to fish when there are no other reefs to swim to. Only a few species of fish that depend on corals will die, while others might be able to find other rocky habitats. It has been difficult to conduct larger-scale studies which can predict what fish species will survive in a world without corals. Giovanni Strona, University of Helsinki, has just published a new study that shows global projections of fish biodiversity without corals are not as accurate as small-scale studies suggest.A team of international marine biologists began mapping the diversity of tropical fish and corals across the oceans around the globe for each square degree latitude or longitude. These maps confirmed what marine biologists knew for years: fish and coral diversity are very different. There are more species in the Indo Pacific "coral triangle" area than there is in the western Atlantic or eastern Pacific. The way that geography, latitude, habitat and temperature affect speciation rates of fishes and corals has been a key factor in marine diversity hotspots. The authors discovered that diverse coral areas had higher numbers of diverse fishes than those with less corals. This suggests that coral diversity is a driver of fish diversity.This is not surprising, considering corals are a unique food source for certain species and a three-dimensional shelter that many species use. Giovanni Strona, the University of Helsinki's lead author, said that coral-dependent fish could be prey for other fish.The authors performed a simple thought experiment after fitting the line between fish diversity and coral diversity. The authors predicted global coral extinction by extrapolating the fish-corals association until there was no coral species left. This extrapolation showed that approximately 40% of the world's coral reef fishes would disappear if corals disappeared. This is a far greater loss than the species that depend on coral directly or indirectly, which suggests that coral reef food webs could be unraveled if corals disappear. Some areas will experience more severe unravelling than others. It is predicted that the Central Pacific will lose 60% of its reef fish while only 10% are lost in the Western Atlantic.Strona says, "We developed a statistical model that disentangles the effect of history, environment, and biogeography on fish and coral diversity. It accurately predicts local-scale fish diversity as an response to various environmental variables like water temperature, pH, salinity, and coral diversity."Valeriano Parravicini is a co-leader of the University of Perpignan study.This thought experiment is for anyone who has ever enjoyed snorkeling on coral reefs, and for millions of people who rely on reef fishes as food. It also encourages more efforts to preserve and restore coral reefs. It would benefit corals as well as fish and other organisms dependent on corals." Kevin Lafferty is a Senior Scientist at the U.S. Geological Survey at the University of California Santa Barbara.###