Some corals and reefs are showing surprising resilience as global waters warm

The world’s coral reefs, aside from a few that are showing surprising resilience, have been facing unprecedented challenges over the past four decades. This is largely due to the adverse effects of climate change, pollution, unsustainable coastal development, and overfishing.

Scleractinian corals, commonly known as hard corals, have been particularly impacted. However, a ray of hope shines through the resilience of some Caribbean octocorals, also known as soft corals.

Studying soft coral resilience

Mary Alice Coffroth, a respected professor emerita of geology at the University at Buffalo, led a significant study on the resilience of soft corals. Over two years, Coffroth and her team at UB conducted an extensive survey in the Florida Keys.

Their focus was on three species of octocorals that demonstrated an ability to survive heat waves. Coffroth emphasized the importance of this finding, stating, “The resistance and resilience of Caribbean octocorals offers clues for the future of coral reefs.”

Coffroth led a dedicated team including graduate student Louis Buccella, undergraduates Katherine Eaton and Alyssa Gooding, technician Harleena Franklin, and Howard Lasker, professor emeritus. Between 2015 and 2017, they focused on the symbiotic relationship between the octocorals and their algae.

Hard and soft corals rely on symbiosis with single-celled algae. Warmer waters disrupt this relationship, leading to bleaching. Coffroth, who has been studying coral reefs in the Florida Keys since 1998, explained, “Bleaching can lead to coral death. It’s unclear if the algae leave or are ejected from the coral.”

In this study, they examined the mechanisms contributing to the heightened resistance and resilience of three octocoral species during marine heat waves leading to bleaching events. This involved following the genetic makeup and density of symbiont algae before, during, and after major heat waves.

What the researchers discovered

Coffroth discovered that Caribbean octocorals predominantly harbor Breviolum symbionts. These symbionts declined in density during heatwaves but recovered quickly, contributing to lower octocoral mortality compared to their scleractinian counterparts.

“The Breviolum densities declined during the heatwaves but recovered quickly,” she explained. “Octocoral mortality was low compared to their scleractinian relatives.”

Following the 2014 El Niño and anticipating a similar event, Coffroth successfully applied for a Rapid Response Research grant from the National Science Foundation. This funding allowed her team to conduct an in-depth 28-month study in the Keys, focusing on the fate of octocorals and their symbionts.

The team’s regular visits to the Keys Marine Lab facilitated detailed observations and sample collections, enabling a comprehensive analysis of coral resilience, coloration, symbiont density, and genetic identity.

Coffroth highlighted the timeliness and relevance of their findings, given the current global warming trends, increased storms, and major bleaching events. She pointed out that corals today are withstanding higher temperatures than in the 1960s.

“There is evidence that corals are withstanding higher temperature now than they did in the 1960s,” she said. “That signals evolution, but the problem is that climate change is moving too fast, faster than evolution.”

Ecological significance of coral reefs

Coral reefs, beyond their stunning beauty, play crucial roles in protecting coastal regions, providing habitats for significant marine life, supporting tourism, and contributing to medical research. Coffroth remarked on the stark contrast between the coral reefs of the 1970s and the present, underscoring the dramatic changes they have undergone.

“If you a see picture of coral reefs when I started diving in the 1970s and compare it with one now, it makes you want to cry,” she said. “The change is just amazing.”

While acknowledging the importance of their observations, Coffroth stressed the need for further research to understand the variations within the coral and symbiont genera. She noted an increase in both the bleaching of coral species that had previously shown resilience, and the emergence of new resilient ones.

“I’m seeing species bleach that have never bleached before but also corals showing more resilience,” she said. “There is a lot of variation within both the animal and symbiont genera. We need to understand the variation.”

The ultimate goal is to continue exploring coral reef dynamics and the robustness of symbiotic algae, alongside efforts to mitigate environmental damage caused by human activities.

Coffroth concluded, “We can’t stop global warming, but the hope is that we can slow it down,” underscoring the urgent need for continued research and action in the face of ongoing environmental challenges.

The full study was published in the journal Science Advances.

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