Great Barrier Reef – Coral Bleaching – Update
Two years after a long-lasting undersea heat wave scalded large sections of the Great Barrier Reef 2016 & 2017), scientists have found that because so many corals died, much of the reef has probably been altered “forever.”
Because it takes about 10 years for even the fastest growing corals to recover, the study warns that there is probably no reversing the sweeping change to the most damaged sectors of the world’s largest barrier reef. Not before yet another bleaching event occurs.
That certainly doesn’t mean the end of the reef as a whole. The south, in particular, escaped much of the bleaching in 2016 and 2017. But it does mean that much of the reef will probably shift into a new ecological state with a less diverse, but more resilient, set of corals.
Extremely warm ocean temperatures stress corals and cause a phenomenon called “bleaching,” in which tiny algae called zooxanthellae abandon the corals they live with, causing the corals to lose their color. The consequence is not just outward — zooxanthellae are partners with coral in an ancient symbiotic relationship, conducting photosynthesis necessary for the corals to survive. If the algae are gone for too long, the corals die.
The new results show that roughly half of the corals along the 1,400 mile long reef died in the past two years of bleaching. The death toll amounts to about a billion corals, but there are another billion remaining.
Yet the remaining billion are disproportionately made up of certain species, especially in the most damaged sectors. Bleaching selectively killed certain types of corals, such as branchy staghorn, while more blocky corals survived.
The deaths did not always occur in the way that was expected — in which zooxanthellae abandon the corals and don’t return fast enough, leading to starvation.
Instead, “we were surprised to see about a 25 percent loss of corals in the north that was more or less instantaneous,” the Report said. “That number of corals died in two weeks. They didn’t die slowly of starvation, they actually cooked.”
There are variations in the appearance of severely bleached corals. Here, the coral displays pink fluorescing tissue signaling heat stress.