The longest experimental coral study, a 22-month project that replicates current and future ocean conditions, suggests Hawaiian corals may remain resilient as climate change makes seawater warmer and more acidic.

The study, led by Rowan McLachlan, a postdoctoral researcher at Oregon State University, was published today in Scientific Reports. The authors, who include Christopher Jury and Robert Toonen from the University of Hawaii at Mānoa, say the research is important because understanding the factors behind coral health is crucial to efforts to save reefs. besieged Earth.

“Our study found that in the absence of local stressors such as nutrient pollution, overfishing, bottom trawling, physical damage from tourism, etc., at least half of the corals in Hawaiian reefs will be able to survive and persist for up to 22 months of exposure to warming and acidifying oceans,” McLachlan said. “The results provide hope that if we can mitigate climate change and meet the goals of the ‘Paris Climate Agreement, coral reefs will persist in some form, but with reduced abundance and genotypic diversity.’

But it’s still unclear how the corals will behave if changes in temperature and acidity are more severe than those used in the research, or how they will behave under current conditions for longer periods of time.

“Our results offer some hope, but the roughly 50% mortality we observed in some species in this study is no small feat,” McLachlan said.

The majority of previous research on the ability of coral reefs to survive and persist under ocean warming and acidification has been acquired from short-term experiments, averaging one month in duration, and based in indoor laboratories in empty glass tanks.

“While informative, these studies are limited in their ability to predict how coral will respond in the wild where the environment is much more complex,” McLachlan said.

In the short period between 2014 and 2017, more than 75% of the world’s coral reefs experienced heat stress at the bleaching level and 30% experienced stress at the mortality level. (Bleaching is the breaking of the symbiotic relationship between corals and the algae they depend on for energy.)

Coral reefs make up less than 1% of the ocean, but are home to almost a quarter of all known marine species. Reefs also help regulate carbon dioxide levels in the sea and are a vital hunting ground that scientists use in the search for new drugs.

McLachlan, a doctoral student at Ohio State University’s Andrea Grottoli Laboratory during the study, and his collaborators collected samples of the three most common species of Hawaiian coral: Montipora capitata, a branching, plated stony coral; Porites compressa, a branching species also known as finger coral; and Porites lobata, which forms rock-like lobes.

The scientists placed the samples in four different outdoor tanks:

• current ocean conditions
• more acidic water (minus 0.2 pH units)
• warmer water (plus 2 degrees Celsius)
• warmer, more acidic water

“We tried to design the experimental tanks to mimic the natural reef environment as closely as possible,” McLachlan said.

The tanks were placed outdoors under natural light and included pumps simulating the natural flow of water. They were filled with seawater pumped directly from a nearby reef and included sand, rocks, fish, algae, crustaceans and other organisms in addition to corals.

McLachlan said these conditions made the study “arguably more realistic and accurate in predicting the future of corals under global climate change.”

The results suggest that warming oceans will harm coral species: 61% of coral samples exposed to warming conditions survived, 31% less than those exposed to current ocean temperatures.

Porites species showed more resilience than M. capitata in the combined warming/acidification treatment. There, survival rates were 71% for P. compressa, 56% for P. lobata, and 46% for M. capitata.

Porites species’ ability to resist rising temperatures and acidification, and their role in building reefs, provide hope that some reef ecosystems may persist despite changing ocean conditions, McLachlan said.

Other co-authors were Grottoli, James Price, Agustí Muñoz-Garcia, and Noah Weisleder from Ohio State; and Stephen Levas of the University of Wisconsin-Whitewater.

The National Science Foundation and the HW Hoover Foundation supported the research.