Scientists say coral reefs need time they no longer have as bleaching accelerates

By Ron Rocky Coloma

Coral reefs around the world are facing a growing challenge that scientists say is no longer defined by a single bleaching event, but by the shrinking amount of time reefs have to recover before the next wave of marine heat arrives, according to marine ecologists.

Mollie Asbury and Tye Kindinger of Pristine Seas said protecting healthy reefs and reducing local pressures can improve the odds of survival for ecosystems that support food security, fisheries and coastal protection across the Pacific.

"Unfortunately, widespread bleaching isn't a warning sign anymore but the current reality across most of the world's reef systems," Asbury said.

She said the greatest concern among scientists is not simply how often bleaching occurs, but how little time reefs now have to recover.

"Reefs used to have roughly a decade between severe bleaching events to recover and now that gap has collapsed to a few years in many regions, which doesn't give coral communities enough time to rebuild before the next heat stress hits," she said. "That's the real crisis: not a single catastrophic event, but a cumulative one, where reefs are needing to recover faster than is biologically possible."

Asbury said research increasingly shows that some reefs are naturally better equipped to recover than others because of measurable characteristics rather than chance.

"The biggest lesson from my work in the Pacific is that resilience isn't random, but tied to specific, identifiable factors," she said.

She pointed to reef structural complexity and previous exposure to warmer temperatures as consistent indicators of resilience.

"For example, reefs with greater structural complexity tend to recover faster and more fully than reefs without those conditions," Asbury said. "The exact shape that complexity takes, not just how much of it there is, turns out to matter just as much."

She said those findings could help conservation groups identify where limited resources would have the greatest impact.

"What that tells us is that resilience isn't just luck, but something we can actually map," she said. "That means we can prioritize protection where it will do the most good, rather than spreading limited resources evenly across reefs with very different odds."

One area of growing scientific interest is remote reefs that have experienced little human disturbance. While those reefs are not immune to rising ocean temperatures, Asbury said they offer valuable comparisons for understanding how coral ecosystems function under fewer local stresses.

"Remote, largely untouched reefs are essentially a natural control group for what reefs look like without the stressors we can control," she said.

According to Asbury, reefs free from heavy fishing pressure, pollution and coastal development often demonstrate how much resilience coral communities can maintain when facing climate-related stress alone.

"It's also the strongest possible argument for marine protected areas: These pristine reefs show us what protection buys a reef, and it's often the difference between a reef that bleaches and dies and one that bleaches and comes back," she said.

Her fieldwork has also challenged assumptions about the relationship between conservation and human use.

During one Pristine Seas expedition, researchers surveyed reefs surrounding what local communities described as "pantry islands," where generations have harvested seafood.

"We found them just as spectacular as fully protected ones," Asbury said. "We saw strong and diverse coral cover, healthy fish biomass, and structurally complex reefs."

Rather than viewing conservation as excluding people, she said the experience highlighted how traditional management practices can support healthy ecosystems.

"What I saw instead was generations of inherited knowledge about how to harvest respectfully in ways that let the reef keep sustaining them," Asbury said. "Conservation doesn't have to mean people versus reefs. We can learn great lessons from these communities, which are already doing it right."

For many Pacific island communities, healthy reefs provide far more than marine habitat.

"A healthy reef does real, tangible work," Asbury said. "It's a functioning seawall that reduces wave energy and storm damage, a fishery that feeds families, and a living part of cultural identity that's been passed down for generations."

She said studies consistently show that well-managed, community-led marine protected areas produce healthier fish populations and stronger coastal

protection than comparable unprotected reefs.

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Kindinger, whose research focuses on reef fish communities, said coral bleaching threatens not only corals themselves but also the fish that rely on reef ecosystems throughout their lives.

"Without a healthy reef, coral-reef fish will eventually disappear," he said.

Fish depend on reefs for shelter, food and reproduction, he said, while climate change also creates additional challenges through warmer waters and changing ocean chemistry.

"It seems likely, however, that as oceans continue to change, the rate at which fish will reach their survival limits will be much slower than the rate at which climate change is already causing coral bleaching and loss," Kindinger said. "So reef loss continues to be of gravest concern for reef fish, since it's already happening at a global scale."

He said the contrast between protected reefs and heavily fished areas is immediately noticeable underwater.

"As a scuba diver, the moment I sink below the surface of the ocean, I know if I'm at a remote, protected reef," Kindinger said.

He described seeing abundant sharks and other predators, colorful reef fish and species that behave differently because they are not regularly hunted.

"In places where they are not fished, they tend to be less scared around boats and divers and can even seem curious," he said.

Protected reefs also tend to support more large food fish, particularly in shallow areas that are typically easier for fishers to reach.

"To put it simply, if you stop fishing in an area, those fish will come back and they will be able to grow bigger, because they're no longer being removed by fishing," Kindinger said.

Healthy fish populations also play an important role in helping reefs recover after bleaching or storm damage.

Herbivorous fish such as parrotfish consume seaweed that would otherwise compete with young corals for space.

"When some of these fish remove seaweed, they also create open space on the reef where a new coral baby (a coral recruit) can settle and grow," Kindinger said.

"The more opportunity there is for new corals to successfully recruit onto a reef and survive, the higher the chance for reef recovery."

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