Coral Species Show Resilience to Ocean Warming and Acidification

Researchers at the UH Hawaiʻi Institute of Marine Biology (HIMB) Toonen-Bowen “ToBo” Lab have conditions under which eight common coral species in Hawaiʻi can adapt to and withstand ocean warming and acidification. The study was published in the Proceedings of the Royal Society B: Biological Sciences.

The corals studied are common in the Indo-Pacific, home to over two-thirds of the world's coral reefs. The research revealed that these corals could survive in a "low climate change scenario," where global carbon dioxide emissions are reduced, and the corals are maintained in controlled lab conditions. However, under "business as usual" carbon dioxide emissions, none of the species in the study could survive.

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. 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.

Christopher Jury, Post-doctoral Researcher and Study Lead Author, Hawaiʻi Institute of Marine Biology

Through a process called "coral calcification," individual coral organisms, or polyps, build their skeletons over time by secreting calcium carbonate, which forms limestone and creates massive reef structures. Researchers use the coral growth rate as an indicator of reef ecosystem health, as corals grow slowly—some colonies expand by less than an inch annually.

To simulate real-world conditions, the ToBo lab research team developed semi-enclosed outdoor "mesocosms" containing various biological species for nearly a year. They observed how the eight coral species responded to calcification under different temperature and acidity levels.

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. 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.

Rob Toonen, Professor and Principal Investigator, Hawaiʻi Institute of Marine Biology

The conditions that coral reefs have evolved to survive for millennia are being rapidly altered by global climate change, and most predictions for the future of coral reefs have been pessimistic. These findings are unexpectedly positive and encouraging.

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

Christopher Jury, Post-doctoral Researcher and Study Lead Author, Hawaiʻi Institute of Marine Biology

Coral reefs provide food, income, and protection for over 500 million people worldwide and are among the most biologically diverse ecosystems on Earth. They serve as sources of food, medicine, recreation, and coastal protection against erosion and storms. The ability of corals to adapt to both acidification and warming will significantly influence their responses to global change in the coming decades.

Most research on coral adaptation has focused on heat tolerance, with few studies examining their ability to adapt to the combined effects of warming and acidification. Even less is known about their adaptability to more acidic conditions. However, an increasing number of studies suggest that many coral species may be more resilient to climate change than previously thought.

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

The study was funded by the National Science Foundation, the University of Hawaii Sea Grant College Program, and the Ocean Acidification Program of the National Oceanic and Atmospheric Administration.

Journal Reference:

Dove, G. S., et al. (2024) Ocean warming and acidification uncouple calcification from calcifier biomass which accelerates coral reef decline. Proceedings of the Royal Society B Biological Sciences. doi.org/10.1038/s43247-020-00054-x