The next ten years will determine whether or not coral reefs will continue to exist in the oceans. “30 percent of coral reefs will survive this century if we limit global warming to 1.5 degrees Celsius,” says Andréa Grottoli, coral researcher at Ohio State University. Half a degree more would mean that 99 percent of the reef-forming corals would disappear.
Grottoli is co-author of a study that was just published at a symposium of the International Coral Reef Society (ICRS). Together with other researchers, she makes it clear that how short the time span is in which the coral reefs can be saved. “Our models show that we only have a few years left,” says Grottoli. “It has to happen in the next ten years, otherwise we won’t make it.”
Coral reefs are one of the most biodiverse ecosystems in the world. They house about a third of all known sea creatures, although they cover less than 0.1 percent of the ocean floor, and are therefore also called the “rainforests of the seas”.
With the cnidarians, fish, mussels, crabs and many other animals would also disappear
The basis of life for all these fish, mussels, crabs, squids and many other species are stony corals, the hard aragonite skeleton of which forms the structure of the reefs. It is precisely this key species that is particularly affected by climate change. On the one hand, when the temperature rises, the water in which the cnidarians live also heats up. If the temperature rises above 30 degrees Celsius, the polyps repel their partners with whom they normally live in symbiosis: tiny algae that supply the cnidarians with sugar and other nutrients and in return receive protection and carbon dioxide. The consequence of the expulsion is the notorious coral bleaching.
The second reason climate change is threatening coral reefs is ocean acidification. If the concentration of carbon dioxide in the atmosphere increases, more CO₂ dissolves in the seawater, and the pH value drops. This can have the consequence that the aragonite skeleton of the hard corals simply dissolves or at least that they no longer grow.
According to the study authors, the coral reefs are at a “tipping point”. If climate change can be halted now, she believes that enough corals could survive to recover once conditions improve. “The fewer coral reefs left, the more difficult it will be to rebuild them later,” says Grottoli.
The study authors see their study as a kind of wake-up call to politicians and therefore emphasize how important coral reefs are for humans. Among other things, they are a kind of natural breakwater and protect coasts from flooding. A healthy reef can significantly reduce the height of the waves and absorb up to 90 percent of their energy, they write. In the United States alone, the reefs would save 18,000 people from flooding each year. This natural protective barrier is particularly important for the inhabitants of the small island states in the Pacific. In addition, fish from coral reefs provide food for millions of people.