Scientists find new coral death in Great Barrier Reef

For months, coral reef experts have been loudly, and sometimes mournfully, announcing that much of the treasured Great Barrier Reef has been hit by “severe” coral bleaching, thanks to abnormally warm ocean waters.

Bleaching, though, isn’t the same as coral death. When symbiotic algae leave corals’ bodies and the animals then turn white or “bleach,” they can still bounce back if environmental conditions improve. The Great Barrier Reef has seen major bleaching in some of its sectors — particularly the more isolated, northern reef — and the expectation has long been that this event would result in significant coral death as well.

Now some of the first figures are coming in confirming that. Diving and aerial surveys of 84 reefs by scientists with the ARC Center of Excellence for Coral Reef Studies at James Cook University, in Australia — the same researchers who recently documented at least some bleaching at 93 percent of individual reefs — have found that a striking 35 percent of corals have died in the northern and central sectors of the reef.

The researchers looked at corals from Townsville, Queensland, all the way to New Guinea, said coral expert Terry Hughes, who led the research — and examined 200,000 corals overall, he said. The 35 percent, the researchers said, is an “initial estimate” that averages estimates taken from different reef regions.

Fortunately, the southern sector of the reef was largely spared, thanks to the ocean churning and rainfall caused by Tropical Cyclone Winston, which cooled waters in the area, Hughes said.

But while coral death numbers are far lower to the south, “an average of 35 percent is quite shocking,” Hughes said. “There’s no other natural phenomenon that can cause that level of coral loss at that kind of scale.”

He noted that tropical cyclones — what Americans call hurricanes — also kill corals at landfall, but typically over an area of about 50 miles. In contrast, the swath of damage from the bleaching event, he says, was “500 miles wide.”