News•July 21, 2016

Local Efforts to Save Coral Reefs May Be Futile

Corals in remote and relatively pristine reefs fare little better overall amid global warming than those growing alongside heavily populated coastlines, according to research published Wednesday.

The new paper, published in Nature’s Scientific Reports by the University of North Carolina, reinvigorated debate among reef scientists over whether local safeguards and programs could save some of the world’s most spectacular and crucial ecosystems from being wiped out.

Fish swarming around staghorn coral in the waters of Fiji.
Credit: Taveuni Palms Resort/Flickr

Scientists agree that coral reefs will continue to be decimated if climate-changing pollution from fossil fuels, farming and deforestation is not addressed.

They disagree, however, over whether local efforts to restrict fishing and reduce water pollution will make meaningful differences in a world of fast-rising temperatures.

Coral reefs nurture fisheries and protect coasts from erosion, but since the 1990s they have been bleaching and sometimes dying off because of warming waters, with acidification, pests and local oxygen declines and water pollution compounding their problems.

As reef scientists find coral graveyards in remote and seemingly pristine waters, they’re also discovering vibrant reefs growing near large human population. That’s left many wondering about the extent to which local efforts to protect reefs from pollution and overfishing matter.

The uncertainty is rooted in the fact that there’s no precedent to the extent of the recent coral die-offs, which are affecting all the world’s reefs amid record-breaking ocean temperatures, from Australia’s Great Barrier Reef to the reefs off India, Florida and Belize.

“The recent global bleaching and mortality event will allow scientists to document the stages of reef recovery,” said Georgia Tech professor Kim Cobb, a leading reef scientist who wasn’t involved with the new study. “One thing seems certain, however — many of the world’s reefs will never be the same.”

The research paper warns of unbridled calamity for coral reefs in the years ahead unless global warming is abruptly slowed — regardless of any local measures taken.

The findings were based on coral surveys taken around the world during a decade that preceded the record-breaking three-year coral bleaching disaster that’s now savaging reefs. Sometimes bleached corals recover; in many cases they die.

Other scientists interpreted Wednesday’s findings differently, characterizing the new report as a reminder that regional efforts can help to protect reefs during an era of fast-rising temperatures.

Most of the heat trapped by greenhouse gas pollution is absorbed by the oceans, which has heated some regions faster than others. High Coral Sea temperatures linked to climate change earlier this year were blamed for widespread bleaching along the Great Barrier Reef, which left some of its best protected corals dead.

“I don't think that any coral reef ecologist would disagree that global climate change is the most widespread and significant threat for the future of coral reefs,” said Jennifer Smith, a marine scientist with Scripps who wasn’t involved with Wednesday’s paper.

A United Nations treaty finalized in Paris in December aims to slow global warming, but countries haven’t yet figured out how they will achieve its goals.

“Promoting the need for global climate policy and a reduction in global carbon emissions is a very important message for the future of coral reefs,” Smith said.

Aside from a shared urgency over the problem of global warming, the report illuminated a rift that has emerged between two camps of reef scientists over the relative importance of local problems — and potential solutions.

At the most basic level, the scientists are divided into pessimists and optimists.

A marine biologist inspects bleached coral in American Samoa.
Credit: XL Catlin Seaview Survey

The pessimists see little point in protecting individual reefs if climate change is not quickly and abruptly slowed. The optimists see local reef protections as critical amid an era of global warming, and tend to focus heavily on how society can adapt to climate change.

The pessimistic camp includes University of North Carolina professor John Bruno, one of two authors of Wednesday’s paper. The other author, Abel Valdivia, recently left the university and joined the staff at the nonprofit Center for Biological Diversity.

Bruno and Valdivia pored over data from coral surveys of 1,708 reefs worldwide between 1996 and 2006, comparing algae and coral cover with the size of the nearby human population. They found that the number of people living in close proximity to a reef is a poor predictor of the health of that reef.

Such research can provide a sense for how humans affect coral reefs locally — but scientists warned it can provide only a very rough sense.

“By just taking one big snapshot of lots of reefs, we do not get a good picture of whether individual reefs have been losing coral over time or gaining coral over time,” said Deron Burkepile, a scientist at the University of California, Santa Barbara. “These large global data analyses have a hard time capturing a lot of the local nuance that many studies show are important.”

The research also didn’t consider local conditions or regulations, which would help illuminate whether the nearby population or nation is actively protecting its reefs. And relative algae and coral cover are just one of many potential indicators of reef health.

To Bruno, the lack of a strong relationship between local population size and reef health indicated that local problems facing reefs and their solutions are trivial when compared with the global problem of climate change.

“That tells us that local conservation alone will not restore reefs,” Bruno said. “It’s essential that we reduce greenhouse gas emissions immediately and drastically.”

Bruno was critical of scientists who argue that local conservation can be effective amid rampant global warming.

“The reason a lot of scientists want to believe local impacts and conservation matter is because they desperately want to be able to offer solutions that don’t require cuts to carbon emissions,” Bruno said.

The optimists’ camp includes Mike Beck, a marine scientist with the nonprofit Nature Conservancy and with the University of California, Santa Cruz.

Beck said the North Carolina scientists “identified a surprising pattern and one reasonable hypothesis that might explain it — climate change is the only driver that matters for coral reefs.”

But he criticized their conclusions as overly pessimistic, and said their data “could equally support a hypothesis that many local management efforts are working” and that such efforts “should get more support.”

Scientists have been surprised to find healthy corals in the waters off Cancun, despite heavy pressures from local populations and tourists.
Credit: f. ermert/Flickr

Beck said pessimism over the future of reefs is overly rife within his field, something he blamed on science itself.

“You’re not going to be made famous by examining local problems and solutions,” Beck said. “It’s only by discussing big global problems and big global solutions that you're going to get a paper published in Nature Scientific Reports.”

In support for his optimism, Beck pointed to research by himself and others indicating reefs are faring better globally than other coastal ecosystems, such as marshes, oyster reefs and mangroves, which are being destroyed as surrounding human populations swell.

A major problem, scientists agree, is a severe shortfall of data and information from scientific studies into coral reefs and their resilience. That’s making it impossible for them to say precisely what the future holds for some of nature’s most spectacular and productive ecosystems.

University of Queensland professor Ove Hoegh-Guldberg, a leading coral reef scientist who focuses on climate change, said “we have yet to really apply ourselves to solving the problems that face coral reefs,” which means it remains unclear “where we have applied the right amount of attention to solving local threats.”

Hoegh-Guldberg praised the North Carolina scientists and said he didn’t doubt the veracity of their data or analysis, but he disputed their bleak message. “The devil is in the interpretation,” he said.

“The message from this research is that we need to double down on the local strategies that will preserve coral reefs into the future,” Hoegh-Guldberg said.

“However, there’s a really important point here,” he said. “This is the fact that a lack of action on climate change, particularly to stabilize ocean temperature and chemistry, will make most, if not all, efforts at the local scale pointless.”

Editor's Note: Deron Burkepile is a scientist at the University of California, Santa Barbara, not Scripps, as this article originally stated.