With curtailed carbon emissions, corals can survive climate change, say researchers

In a study published in Proceedings of the Royal Society B, researchers at the UH Hawaiʻi Institute of Marine Biology (HIMB) Toonen- Bowen “ToBo” Lab have identified scenarios under which eight of the most common species of coral found in Hawaiʻi can adapt to and survive ocean warming and acidification.

The corals in the study are prevalent throughout the Indo-Pacific, a region that comprises more than two-thirds of the coral reefs on planet Earth, and 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 “business-as-usual” carbon dioxide emissions scenario. This finding 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,” explains HIMB post-doctoral researcher and lead author of the study, Christopher Jury.

“None of the coral species are likely to keep up with a high rate of climate change, but all eight can likely keep up with a low rate of change as targeted under the Paris Climate Agreement.”

Massive reef structures are formed over time through a process known as “coral calcification,” where individual coral organisms—or polyps—craft their own skeletons by secreting a salt known as calcium carbonate which becomes limestone. 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 ToBo lab research team used biologically diverse, semi-enclosed outdoor “mesocosms,” to simulate 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,” explains Rob Toonen, 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.”

Global climate change is rapidly altering the conditions coral reefs have adapted to over millennia, and most projections for the future of coral reefs have thus far been grim. These results are highly unexpected, and welcome.

“This was a very surprising result, given the usual projected collapse of coral reefs in Hawai’i and globally under these climate change stressors,” emphasizes 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.”

Over half a billion people depend on coral reefs for food, income, and protection, and reefs are among the most biologically diverse ecosystems on Earth. They protect coastlines from storms and erosion, provide jobs for local communities, and are a source of food, medicine, and recreation.

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.

Mounting evidence indicates that many coral species harbor a greater capacity to adapt to the changing climate than is often appreciated.

“We included the eight most common coral species in Hawai’i, which constitute about 95% of the coral cover on Hawaiian reefs,” says Jury. “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.”