Saving corals requires cutting carbon emissions, University of Hawai‘i study finds

Hawai‘i researchers have discovered that eight of the most common species of coral around the islands can adapt to ocean warming and acidification, but only if efforts to cut carbon emissions are made.

According to a new study at the University of Hawaiʻi at Mānoa Hawaiʻi Institute of Marine Biology, coral throughout the Indo-Pacific, home to more than two-thirds of the earth’s coral reefs, were found to be capable of surviving a “low climate change scenario,” where laboratory conditions reflect a global reduction in carbon dioxide emissions.

Critically, none of the species in the study could withstand a scenario where carbon emissions were not reduced. The study published in Proceedings of the Royal Society B suggests that curtailing carbon dioxide emissions is essential for the survival of coral reefs.

“This study shows that widespread and diverse coral species all exhibit the potential to adapt to the changing climate, but climate change mitigation is essential for them to have a chance at adaptation,” said Christopher Jury, who is an HIMB post-doctoral researcher and lead author of the study.

Massive reef structures are formed over time. Growth is gradual; some coral colonies grow less than an inch each year, and researchers use coral growth rate as an indicator of reef ecosystem health. For nearly one year, the research team simulated realistic field conditions. They controlled levels of temperature and acidity, and measured the calcification responses of the eight species of coral.

“When we analyzed how the corals performed under warmer, more acidic conditions, we found that about one-quarter to one-half of their tolerance is inherited through their genes,” said Robert Toonen, research professor at HIMB and principal investigator of the project. “That means the ability to survive under future ocean conditions can be passed along to future generations, allowing corals to adapt to ocean warming and acidification.”

“This was a very surprising result, given the usual projected collapse of coral reefs in Hawai‘i and globally under these climate change stressors,” said Jury. “Most projections are that corals will be almost entirely wiped out, and coral reefs will collapse within the next few decades because corals cannot adapt fast enough to make a meaningful difference. This study shows that is not true, and we still have an opportunity to preserve coral reefs.”

The ability for corals to adapt to combined warming and acidification will play a key role in their responses to global change over coming decades. Most studies examining their ability to adapt have focused on heat tolerance. Far less is known about corals’ capacity to adapt to more acidic conditions, and very few studies have examined their capacity to adapt to the combination of warming and acidification. Evidence indicates they may be better at adapting to the changing climate.

“By understanding how these species respond to climate change, we have a better understanding of how Hawaiian reefs will change over time and how to better allocate resources as well as plan for the future,” said Jury.

Funding was provided by the National Science Foundation, UH Sea Grant College Program, and the National Oceanic and Atmospheric Administration’s Ocean Acidification Program.