Given that coral reefs support some of the most biodiverse ecosystems on the planet and peoples’ livelihoods, food security, and safety, it is a matter of grave concern that the massive coral bleaching episode signalled by US authorities last month is expanding and deepening in reefs around the globe, as scientists warned last Thursday. Amid record ocean temperatures, coral bleaching has been recorded in 62 countries and territories since February 2023, the US National Oceanic and Atmospheric Administration (NOAA) said — an increase of nine from its warning in April.
“This event is still growing in size and impacts,” Derek Manzello, co-ordinator for NOAA’s Coral Reef Watch programme, told a press briefing, adding: “This is not something that would be happening without climate change.”New coral damage since NOAA’s April 15 warning was reported in India, Sri Lanka and the Chagos islands in the Indian Ocean, Manzello said.
Severe or prolonged heat stress leads to corals dying off, though there is a possibility for recovery if temperatures drop and other stressors such as overfishing and pollution are reduced. Thousands of marine animals depend on coral reefs for survival, including some species of sea turtles, fish, crabs, shrimp, jellyfish, sea birds, starfish, and more. Coral reefs provide shelter, spawning grounds, and protection from predators. They also support organisms at the base of ocean food chains. As reef ecosystems collapse, already at-risk species may face extinction.
Coral reefs are natural barriers that absorb the force of waves and storm surges, keeping coastal communities safe. Without them, we must rely on manmade seawalls that are expensive, less effective, and environmentally damaging to construct. Bleached coral also compounds the overfishing crisis by removing links in the food web and depriving some fish and crustacean species of a place to spawn and develop. Anyone relying on these animals as a primary source of income or protein will be in trouble. Reef tourism brings in billions of dollars each year and supports thousands of jobs. Bleached coral reefs, devoid of magnificent marine species, jeopardise it all
Coral bleaching happens when corals lose their vibrant colours and turn white. But there’s a lot more to it than that. Coral are bright and colourful because of microscopic algae called zooxanthellae, which live within the coral in a mutually beneficial relationship, each helping the other survive. But when the ocean environment changes — if it gets too hot, for instance — the coral stresses out and expels the algae. As the algae leaves, the coral fades until it looks like it’s been bleached. If the temperature stays high, the coral won’t let the algae back, and the coral will die.
The leading cause of coral bleaching is climate change. A warming planet means a warming ocean, and a change in water temperature — as little as 2 degrees Fahrenheit — can cause coral to drive out algae. Coral may bleach for other reasons, like extremely low tides, pollution, or too much sunlight. Coral bleaching matters because once these corals die, reefs rarely come back. With few corals surviving, they struggle to reproduce, and entire reef ecosystems, on which people and wildlife depend, deteriorate.
Bleaching also matters because it’s not an isolated phenomenon. According to the NOAA, between 2014 and 2017 around 75% of the world’s tropical coral reefs experienced heat-stress severe enough to trigger bleaching. For 30% of the world’s reefs, that heat-stress was enough to kill coral. The ongoing mass coral bleaching is the world’s fourth on record, with three others occurring between 1998 to 2017.
Some 60.5% of the world’s reefs have experienced bleach-level heat in the last 12 months, a record, according to NOAA. The previous widespread global bleaching, which occurred from 2014 to 2017, retains the record for the greatest cumulative impact — for now.
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