Some of Earth’s most vivid landscapes are underwater — and they are vanishing twice as fast as tropical rainforests. The exploding colours and patterns of lush coral reefs may disappear in 20 years’ time, say scientists after the first comprehensive survey of coral reefs in the Indo-Pacific region — home to 75 per cent of the world’s reefs.
These wonders are warm, clear, shallow ocean habitats that harbour a quarter of all marine life, usually developing near land, in the tropics. Coral polyps — tiny animals that live in colonies — form the reef’s massive structure. When they die, they leave behind the stony, branching structure made of limestone, which provides shelter for thousands of unique plants and animals, from sponges, crabs, and lobsters, to small fishes. Algae called zooxanthellae inside corals’ bodies provide carbohydrates and oxygen through photosynthesis. So corals don’t grow in waters that are too cold, deep or murky, as they need sufficient light to photosynthesise.
Corals are environmentally important because they recycle CO2. When corals pull calcium, or strontium, from seawater to produce their calcium carbonate shells, they lay down layers of environmental records. This forms a catalogue of the sea’s temperature stretching back thousands of years, revealing monsoon and drought patterns. Corals are also sources of new medicines.
But, alas, these ‘nurseries of the ocean’ are vulnerable to hurricanes, and fish, snails, worms, and starfish feast on them. Humans pose even bigger threats: bad fishing practices, and global warming and pollution, make seas warmer, triggering ‘coral bleaching’ that kills algae and turns entire reefs white. Australia's Great Barrier Reef – the largest reef system in the world — for example, will lose 95 per cent of its living coral by 2050. A lot depends on scientists’ efforts to inoculate corals with heat-tolerant symbiotic algae that could help them survive such ‘bleaching’ events.