There have been ample warnings about the dire fate of the world’s coral reefs as the ocean grows warmer under the spell of climate change.

But the results of a new long-term experiment conducted at the University of Hawaii indicate that some of the most common species of coral in Hawaii are more resilient than previously thought.

A study published this month in the journal Scientific Reports found the coral species experienced significant mortality under conditions that simulated ocean temperatures and acidity expected later this century under the Paris Climate Agreement.

But none of them completely died off, and some were actually thriving by the end of the 22-month study.

“It was very surprising,” said Chris Jury, a postdoctoral researcher at UH’s Institute of Marine Biology and study co-author.

Projections suggested 99% of the coral would die before the end of the experiment.

“We didn’t come close to that,” he said.

Instead, the results showed that 61% of the corals exposed to the warming conditions survived, compared with 92% exposed to current ocean temperatures.

“It’s clear that corals are in a lot of trouble due to climate change, but our study also makes it clear that there are reasons for hope,” Jury said.

The research — billed as the longest ocean warming and acidification controlled experiment on corals to date — was led by a doctoral student at Ohio State University, Rowan McLachlan, who is now at Oregon State University.

As many as a couple dozen papers are expected to emerge from the project involving 40 outside aquarium tanks at the Hawaii Institute for Marine Biology that simulated actual conditions of the ocean.

In the tanks were rocks, starfish, urchins, crabs and fish in oceanlike conditions with natural varying temperatures and pH levels over the course of each day and over seasons.

Jury, the UH coral researcher, spent more than two years working seven days a week to ensure the tanks were in working condition and maintaining their integrity for the study.

Most similar studies are of much shorter duration and rely on modeling to predict the future, he said. In this controlled experiment over nearly two years, the scientists were able to peek into the future with their own eyes.

Coral reefs are threatened worldwide by the growing impacts of climate change. Rising levels of carbon dioxide in the atmosphere have led to warmer oceans, and 25% of the carbon dioxide is absorbed by the ocean, causing it to become more acidic.

Samples of three of the most common coral species in Hawaii — Montipora capitata, Porites compressa and Porites lobata — were placed in tanks with four different conditions: control tanks with current ocean conditions, an ocean acidification condition, an ocean warming condition and a condition that combined warming and acidification.

The two Porites species were more resilient than M. capitata in the combined warming and acidification condition. Survival rates were 71% for P. compressa, 56% for P. lobata and 46% for M. capitata over the course of the study.

The surviving Porites species were able to maintain normal growth and metabolism, offering hope beyond Hawaii as they are among the most common types of coral across the world and have a key role in reef building.

“We found surprisingly positive outcomes in our study. We don’t get a lot of that in the coral research field when it comes to the effects of warming oceans,” McLachlan told Ohio State News.

While there is reason for hope, the study didn’t measure any of the local environmental stressors on coral reefs, including pollution and overfishing.

Jury said reefs are being assaulted on multiple fronts, from ocean warming and acidification to local impacts such as destructive fishing practices, sedimentation and coastal pollution.

“These are serious problems but they are also fixable problems,” he said. “With sensible action we can help to ensure that there will still be healthy coral reefs during our lifetimes and for the generations that come after us.”

Funding for the research was provided by the National Science Foundation, UH Sea Grant College Program and HW Hoover Foundation.