Experiments find coral reefs more resilient to climate change than previously thought

Coral reefs may have a brighter future than previously thought—if carbon emissions are reduced and local stressors like pollution are addressed, reefs could adapt and persist even under climate change.

That’s the promising outlook from a study in “Proceedings of the National Academy of Sciences” led by researchers at the University of Hawaiʻi at Mānoa’s Hawaiʻi Institute of Marine Biology (HIMB). The work was conducted by the Toonen-Bowen “ToBo” Lab, with partners at UH Mānoa and The Ohio State University.

For two years, the researchers changed levels of temperature and acidity to 40 experimental reef systems and measured the calcification responses of the marine life. They found that the reefs didn’t collapse; instead, they persisted as new reef communities.

“This was a very surprising result, since almost all projections of reef futures suggest that the corals should have almost entirely died, the reef communities should have experienced net carbonate dissolution, and reef biodiversity should have collapsed,” said Christopher Jury, HIMB post-doctoral researcher and lead author of the study. “None of those things happened in this study.”

HIMB researchers created the experimental systems, known as “mesocosms,” to mimic the environment of a coral reef in the wild. They included eight Hawaiian coral species, reef sand, rubble and marine creatures, representing one of the most diverse ecosystems on the planet.

“We included the eight most common coral species in Hawai‘i, which constitute about 95% of the coral cover on Hawaiian reefs, and many of the most common coral types across the Pacific and Indian Oceans,” said Jury.

Over two years, the team exposed the mesocosms to different scenarios of higher temperature, higher acidity or a combination of both ocean stressors to see how the reef communities would react to future climate scenarios. 

The team made attempts to include the entire complement of reef species, from microbes, to algae, invertebrates, and fish, under realistic conditions, according to Rob Toonen, HIMB professor and Ruth Gates Endowed chair, who was co-senior author of the study.

“These more realistic mesocosm experiments help us to understand how coral reefs will change over time,” said Tonnen.

Carbon emissions still must decrease, authors say

According to the authors, with effective and timely climate change mitigation measures in place, coral reefs will continue to change, but global reef collapse may still be avoidable.

“The recognition that coral reefs are not doomed if we take appropriate action on climate change and local stressors reinforces the need to accomplish these goals,” said Jury. “Under potential future ocean warming and acidification, coral reef communities will change substantially, but are unlikely to collapse if global change is limited to Paris Climate Agreement targets and local stressors are adequately addressed.”

This research is funded by Hawaiʻi Sea Grant; the National Oceanic and Atmospheric Administration’s Ocean Acidification Program; NOAA OAP; Herbert W Hoover Foundation; Sigma Xi Scientific Honor Society National and Ohio State Chapters; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) fellowship and Clear Reef funds; and National Science Foundation.

View the full article here.