For the success of coral restoration, a matter of scale.

This past June, scientists declared that a third massive global bleaching event, in which large sections of the Great Barrier Reef were damaged, finally seemed to be easing. Despite the relative calm, however, there’s much debate about how to protect these underwater creatures before the next round of bleaching occurs.

News stories over the past few years have highlighted restoration efforts — where coral is grown in a nursery and planted back onto coral skeletons — as “life-saving.” But they often fail to note that these projects are relatively small in scale, leading some critics to argue that the time and resources put towards them would be better spent on improving policy.

Joshua Cinner, a reef expert at James Cook University in Australia, is one such critic who thinks the presentation of coral restoration is lopsided.

“I agree that restoration is better than doing nothing, but your options aren’t doing nothing or doing restoration,” Cinner said. “The millions of dollars spent on restoration could be spent improving water quality, managing fisheries, and reducing impacts of tourists. If well done, these all can have tangible impacts on improving coral reefs.”

Corals get their color from the symbiotic algae that lives within them. As ocean temperatures rise, however, corals become stressed and expel the algae, leaving them white and without a source of nutrients. Bleached coral can recover, but only if temperatures quickly return to normal and other threats like pollution are kept at bay. Climate models suggest that our current rate of greenhouse gas emissions will lead to annual bleaching events by 2050.

Coral reefs cover less than 1 percent of the ocean floor, but they provide habitat for a quarter of all marine species. With one estimate putting their global economic value at nearly $30 billion a year, coral reef decline has consequences for hundreds of millions of people who depend on them for fishing, tourism, and coastal protection. Indeed, in assessing the damage Hurricane Irma caused in Florida this month, scientists said the degradation of reefs across the Caribbean and Florida weakened their ability to act as a buffer and led to worse flooding than otherwise would have occurred.

Given all this, restoring coral via a nursery is a captivating idea. If corals can be healthily grown in large numbers to replant nearby reefs, we can buy “a little time,” as Christopher Page a biologist with Mote Marine Laboratory in Sarasota, Florida, told The Times a few years ago. Page even suggested that using nursery-grown coral, “may be our last, best chance,” for saving coral in the Florida Keys.

But buying time is just that. As Cinner stresses, re-growing coral doesn’t address the actual causes of reef decline, “such as overfishing, climate change, and pollution.”

He pointed to a 2013 study he co-authored in Frontiers in Ecology and the Environment that tracked reef regrowth in Kaneohe Bay, Hawaii after diverting a sewage outfall that was leading directly into the bay. Improving water quality helped reverse an unwanted phase shift, or a transition to a different suite of organisms within the reef structure — this case, one that would reduce the likelihood that coral could survive in large enough quantities.

Nurseries like Mote’s require that the ocean water be relatively stable and devoid of toxins for coral growth. They’re also expensive to set up and maintain. Cinner’s colleague, Terry Hughes, director of the Australian Research Council Center of Excellence for Coral Reef Studies, calculated that one square meter of coral gardening costs $200 to $500.

That’s not to say restoration isn’t feasible on some level. A recent Mote fact sheet states a goal of restoring 1,000 acres, or 1.5 square miles, of reef in the Florida Keys within the next 10 years. The entire Florida Reef tract, however, is 600 square miles.

The Great Barrier Reef — the world’s largest — is over 200 times that size. And according to Hughes, it would cost trillions of dollars to restore the nearly 1,000-mile stretch of coral lost there.

But coral restoration efforts aren’t really aiming for success on that scale, said Rebecca Albright, assistant curator of Invertebrate Zoology and Geology at the California Academy of Sciences. “Most programs that are successful are the scale of a hectare. Meanwhile, global destruction is thousands of hectares — reef restoration is not going to recover global destruction.”

Albright, who does work to conserve reefs in many countries, sees restoration as trying to keep certain reef ecosystems alive while national and international policy toward warming oceans is dysfunctional, at best.

“In a perfect scenario, if we could address the underlying causes,” of climate change through policy, Albright said, “then yes, that’s the answer. But we can’t seem to change the political mindset. I’d be skeptical of funneling reef restoration money to political change. It hasn’t happened before, so why would it suddenly happen now?”

With the looming threat of another round of bleaching, nursey grown coral may even have some benefit besides simply replacing what’s been lost. Andrew Ross, a marine biologist and founder of Seascape Caribbean, a for-profit coral restoration company with clients like Round Hill Hotel in Jamaica, said he’s seen the staghorn species he’s propagating come back hardier after being grown in a nursery. A study published in September in Coral Reefs points to genetic variability and differences in plasticity for nursery-raised Staghorn corals.

“When you put [corals] into a nursery, you get these beautiful branching rates,” Ross said. As the coral growth accelerates, “you see a lot of spawning,” he said. “They’re shooting up babies once a year.”

Nurseries like Seascape Caribbean’s are generally located at more shallow depths than the reef itself, allowing researchers and restorers more control over the health of the animals. They also might serve as a way to salvage the genetics within a particular area of a reef. But that doesn’t mean these corals can necessarily return to their original reef location — just that they thrive where the scientists can monitor their health.

Ultimately, there likely isn’t a single correct approach. In terms of how the issue is characterized in the media, Albright believes coverage has highlighted both sides of the debate — though it might be giving readers too positive of an impression. 

“We need to recognize that realistically — that this is one of many things that is being explored [to] buy us some time,” while we change the root causes of the destruction.

Steve Palumbi, a professor of marine sciences at Stanford University, takes a similar view.

“There are times and places where some judicious help can goose along the natural system and help it recover,” he said.

Palumbi recently completed work with a team of researchers at the northern atoll of Kayangel in Palau, an island nation in the western Pacific, where they showed the community there how to plant coral fragments. Typhoons had damaged large areas of the lagoon, but other conditions such as clean water and low algal cover made it possible for the researchers to plant fragments.

“Re-growing corals won’t work in areas in which the basic reason they died off in the first place has not been fixed,” Palumbi said. As he put it, there’s “no point in trying to put a vegetable garden on a landfill.” But if temperatures continue to climb, no part of the ocean will be amenable to nurseries and replanting.

“Overall, corals will have a very hard time surviving after the next century unless we solve the carbon emission problem, something no number of coral fragments can accomplish,” Palumbi said.

Haniya Rae is a journalist for Consumer Reports and frequently writes for publications including The Atlantic, Popular Science, and Sierra Magazine. She currently cares for her own coral fragments in Brooklyn, New York.