Coral reefs may be more resilient than we thought

Recent research led by the Hawaiʻi Institute of Marine Biology (HIMB) at the University of Hawai‘i at Mānoa challenges the commonly held belief that coral reefs face inevitable decline. 

Led by the Toonen-Bowen “ToBo” Lab at HIMB with collaboration from the Ohio State University, the study shows that coral reefs have the potential to adapt and survive in changing climates if carbon emissions are reduced and local stressors are managed effectively.

Innovative experimental design

Researchers constructed 40 experimental “mesocosms” in a laboratory near the coral reefs, replicating the conditions and biodiversity found in nature. 

The mesocosms included eight common Hawaiian coral species along with reef sand, rubble, and various organisms that create a mini-ecosystem reflective of wild reefs. 

For two years, these mesocosms were subjected to controlled levels of higher temperatures, increased acidity, or a combination of both to simulate potential future climate conditions.

“We included the eight most common coral species in Hawai‘i, which constitute about 95% of the coral cover on Hawaiian reefs,” explained lead author Christopher Jury, a postdoctoral fellow at HIMB. 

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

The process of coral calcification

Coral reefs form over time through calcification, where individual coral polyps secrete calcium carbonate to create limestone structures. 

However, various organisms naturally erode these reefs. If reef erosion surpasses calcification, coral structures and the vast array of species that depend on them may vanish. 

The ToBo Lab closely monitored how temperature and acidity affected calcification and reef health in the mesocosms.

Surprising results challenge projections

Contrary to widespread projections, the experimental reef communities did not collapse but persisted and adapted. 

“These experimental reef communities persisted as new reef communities rather than collapsing,” Jury said. 

“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.”

This result suggests that under controlled, realistic conditions that account for diverse reef organisms – including microbes, algae, invertebrates, and fish – reefs demonstrate resilience. 

“Rather than focusing on just one or two species in isolation, we included the entire complement of reef species from microbes, to algae, invertebrates, and fish, under realistic conditions they would experience in nature,” noted co-senior author Rob Toonen, the co-director of the UH Marine Biology Graduate Program. 

This comprehensive approach is a key differentiator that sets the ToBo Lab’s study apart from traditional, more limited research.

Implications for coral conservation

The findings offer a renewed sense of hope for coral conservation strategies. Coral reefs, known for their rich biodiversity, support millions of people globally, providing resources and livelihoods. However, they are vulnerable to the impacts of ocean warming and acidification due to climate change. 

“Reefs are not inevitably doomed. 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,” Jury said.

The study highlights that, while reefs will undergo significant changes under future ocean conditions, a total collapse can be avoided if global warming is kept within the Paris Climate Agreement targets and local environmental pressures are managed.

Future of coral reef research 

Rob Toonen and his colleagues are optimistic about the future of coral reef research and conservation, advocating for proactive and science-based measures. 

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

The study also sets a precedent for future research aimed at developing effective strategies to preserve coral reef ecosystems amidst a changing climate.

This breakthrough suggests that with urgent climate action and localized efforts, coral reefs can remain resilient. 

The research underscores the critical importance of climate change mitigation and localized protective measures, showcasing that nature’s resilience can be leveraged if humanity rises to the challenge.

The study is published in the Proceedings of the National Academy of Sciences. 

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