The Great Barrier Reef Is Losing Its Strength to Fight Climate Change

Greater levels of climate-related stress make it harder for corals to bounce back from bleaching events.
(Photo: Peter Mumby)
Apr 14, 2016· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

The coral bleaching events plaguing the Great Barrier Reef will worsen in the future as the reef loses its ability to bounce back from traumatic events, research published today in the journal Science has found.

The key here is stress—or more specifically, what researchers call “pre-stress.” Historically, warming waters that trigger coral bleaching events have stepped up gradually. That gives the coral time to adapt and increases their ability to recover.

“When corals are exposed to a pre-stress period in the weeks before bleaching, as temperatures start to climb, this acts like a practice run and prepares the coral,” lead author Tracy Ainsworth of the ARC Centre of Excellence for Coral Reef Studies said in a statement. “Corals that are exposed to this pattern are then less stressed and more tolerant when bleaching does occur.”

The researchers examined nearly three decades’ worth of satellite data and found that these pre-stress conditions occurred before all previous Great Barrier Reef bleaching events.

Unfortunately, climate change threatens to eliminate that pre-stress period. It won’t take much: just an increase of seawater temperatures of 0.5 degrees Celsius—well within the scope of climate models for the next few decades.

RELATED: How to Save a Coral Reef

So what happens without this pre-stress “practice run”? The researchers conducted studies on Acropora aspera, one of many staghorn coral species that make up the Great Barrier Reef. In lab tests, they exposed the coral to different temperature increases—0.5 degrees, 1 degree, and 2 degrees Celsius—and different rates at which those temperature increases happened.

Coral bleaching. (Photo: Peter Mumby)

The testing showed that slow increases in temperature allowed the coral to build up “thermal tolerance” that reduced both bleaching and coral-cell death. The corals were able to bounce back from this stressful period.

But when tested under a quick increase in temperature—as expected in climate-change models—the coral showed more bleaching and greater levels of cell death. Overall, the corals had more trouble recovering.

The researchers warn that without this pre-stress practice run, coral bleaching will occur more often and be more severe. So far, according to the paper, most of the Great Barrier Reef has only experienced temperature increases that allow it to maintain its protected thermal tolerance. That’s expected to change as the climate warms. Not only will the reefs degrade faster, they will stay degraded, unlike most coral bleaching events of the past few decades.

But this is not all about the future. Although the paper doesn’t cover the current bleaching event affecting the Great Barrier Reef, early data suggest that some parts of the 1,200-mile-long reef did not experience a pre-stress period this year. That could make this year’s damage even greater than predicted and spells trouble for the hundreds of marine species that depend on the reef for food and shelter.

So what can be done? The study’s authors wrote that finding out which parts of the reef are most susceptible to these temperature stress events could allow management authorities to reduce other threats to the reefs, such as pollution, and give the corals a chance to bounce back.