No longer in the pink
The world is going to have to start thinking radically to save its coral reefs
Corals are comeback creatures. As the world froze and melted and sea levels rose and fell over 30,000 years, Australia’s Great Barrier Reef, which is roughly the size of Italy, died and revived five times. But now, thanks to human activity, corals face the most complex concoction of conditions they have yet had to deal with. Even these hardy invertebrates may struggle to come through their latest challenge without a bit of help.
According to the Intergovernmental Panel on Climate Change, a rise in global temperatures of 1.5°C relative to pre-industrial times could cause coral reefs to decline by 70-90%. The planet is about 1°C hotter than in the 19th century and its seas are becoming warmer, stormier and more acidic. This is already affecting relations between corals and the single-celled algae with which they live symbiotically, and which give them their colour. When waters become unusually warm, corals eject the algae, leaving reefs a ghostly white. This “bleaching” is happening five times as often as it did in the 1970s. The most recent such event, between 2014 and 2017, affected about three-quarters of the world’s reefs. Meanwhile the changing chemistry of the oceans lowers the abundance of carbonate ions, making it harder for corals to form their skeletons.
If corals go, divers and marine biologists are not the only people who will miss them. Reefs take up a fraction of a percent of the sea floor, but support a quarter of the planet’s fish biodiversity. The fish that reefs shelter are especially valuable to their poorest human neighbours, many of whom depend on them as a source of protein. Roughly an eighth of the world’s population lives within 100km of a reef. Corals also protect 150,000km of shoreline in more than 100 countries and territories from the ocean’s buffeting, as well as generating billions of dollars in tourism revenue. In the Coral Triangle, an area of water stretching across South-East Asia and into the Pacific which is home to three-quarters of known coral species, more than 130m people rely on reefs for food and for their livelihoods in fishing and tourism.