Marine heatwaves cause unprecedented damage to Australian coral

Climate Progress

The Earth’s oceans are warming rapidly, absorbing about 90 percent of the heat created by anthropogenic climate change. Now, new research shows that this heat has caused “almost unprecedented” damage to ancient corals of the coast of Western Australia.

The research, which has yet to be published but is part of a five-year study out of the University of Western Australia, found that, in the summer of 2012-2013, a marine heat wave killed off 400-year-old porites corals, which had previously been thought to be some of the more resistant to the effects of climate change. The coral’s survival depends on algae, but that algae was destroyed by the marine heatwave, causing the coral to become bleached and more susceptible to death.

The study’s researchers told the Guardian that the damage these ancient corals suffered was a major shock.

“To see them badly damaged, or completely dead, as a result of bleachings that happened over previous years, and likely the one in 2013, was surprising,” lead scientist Russ Babcock said.

This isn’t the first time extreme heat has damaged ocean coral. The scientists said bleaching has been occurring for about 20 years, and that records show it has become more common in recent years. In 2010, corals across the world’s oceans became bleached — shedding the algae that provide them much of their food and color — due to heat stress, just the second known global bleaching of coral in history.

“It is a lot easier for oceans to heat up above the corals’ thresholds for bleaching when climate change is warming the baseline temperatures,” C. Mark Eakin of the the National Oceanic and Atmospheric Administration told the New York Times in 2010. “If you get an event like El Niño or you just get a hot summer, it’s going to be on top of the warmest temperatures we’ve ever seen.”

Coral are also threatened by ocean acidification, because more acid in the oceans means less carbonate ions, which are required for reef building. Recent research has found that rate of ocean acidification today is unprecedented, with oceans acidifying faster today than any time in the last 300 million years. That acidification affects more than just coral — increasingly acidic ocean waters can hamper shellfish larvae’s ability to grow shells, which is already hurting the shellfish industry in the U.S.

Ocean acidification has also been found to make fish hyperactive or confused, causing them to be less fearful of predators. And new research has found that ocean acidification could hamper fishes’ eyesight, leaving them vulnerable to predators.

Ocean acidification, heat and decreasing oxygen are all threats that researchers have referred to as a “deadly trio” of stressors affecting the ocean. One report from the International Programme on the State of the Oceans recommended that governments take fast action on climate change and overfishing in order to alleviate these ocean stressors.

Source: Climate Progress. Reproduced with permission.