Study identifies key algae species that help soft corals survive warming oceans

Scleractinian corals, or stony corals, have disappeared globally over the past four decades, due to climate change, pollution, unsustainable coastal development and overfishing. However, some Caribbean octocorals, or soft corals, do not suffer the same fate.

During a two-year study of soft corals in the Florida Keys, Mary Alice Coffroth, professor emeritus of geology at the University at Buffalo, along with a small team of UB researchers, identified three species of octocorals that survived heat waves. Although the coral animal itself may be heat tolerant, Coffroth said his team concluded that the symbiotic algae inside the coral served as a protector of sorts.

“The resistance and resilience of Caribbean octocorals offer clues to the future of coral reefs,” Coffroth said.

A recent paper describing their research, “What Makes a Winner? Symbiont and Host Dynamics Determine the Resilience of Caribbean Octocorals to Bleaching,” was published Nov. 22 in Scientists progress.

Coffroth is the lead author of the study, which she conducted between 2015 and 2017 with graduate student Louis Buccella, undergraduates Katherine Eaton and Alyssa Gooding, and technician Harleena Franklin. Howard Lasker, professor emeritus in the departments of environment, sustainability and geology, also contributed to the study.

Algae helps corals survive heat waves

Hard and soft corals depend on a nutritional symbiosis with the unicellular algae living in their tissues. Warmer waters can cause the symbiosis to break down, leading to a loss of algae symbionts, turning corals white, a phenomenon known as bleaching.

“Bleaching can lead to coral death,” said Coffroth, who has studied coral reefs in the Florida Keys since 1998, including a more recent study in 2020-2021. “It is not known whether the algae leaves the coral or is ejected.

“In this study, we examined possible mechanisms that contribute to the increased resistance and resilience of three octocoral species to recurring marine heatwaves leading to bleaching events,” Coffroth said, noting that it This is the first study to follow both symbionts. Genetic constitution and density of Caribbean octocorals before, during and after a major heatwave.

Overall, Caribbean octocorals harbor symbionts of the genus Breviolum, she said. And this symbiont helps make the octocoral better able to handle the increasing heat.

“Breviolum densities decreased during heatwaves but quickly recovered,” she explained. “Octocoral mortality was low compared to that of their scleractinian relatives.”

El Niño of 2014 prompted research

When Coffroth saw bleached corals during the 2014 El Niño event and knew a similar event was planned for the following summer, she applied for a Rapid Response Research (RAPID) grant from the National Science Foundation. She received $56,305 and, with her master’s student, Buccella, conducted the study in the Keys, tracking the fate of octocorals and their symbionts for 28 months.

She and other team members traveled to the Keys Marine Lab at the Florida Institute of Oceanography to study octocorals in the spring and fall of 2015 and 2016 and in the spring and summer of 2017, recording coloring corals and taking samples to study the density of the symbionts and their genetic identity.

“We knew it was critical to follow individual colonies throughout an event with long-term monitoring of host and symbiont responses,” she said, “and to examine the response at least at the level of symbiont species, if not genotype, to identify potentially resilient species.

Climate change is evolving faster than coral evolution

Although the study began nearly a decade ago, Coffroth said the results are extremely relevant because they reflect what is happening now, with continued warming of ocean waters, increased storms and major events money laundering across the world.

“There is evidence that corals today are resistant to higher temperatures than in the 1960s,” she said. “It indicates evolution, but the problem is that climate change is moving too fast, faster than evolution.”

In addition to their beautiful aesthetic, coral reefs provide many benefits to the planet and its inhabitants, including barriers for coastal regions susceptible to hurricanes and other tropical storms; habitat for large fish such as grouper and snapper; a tourist destination for snorkeling, fishing and scuba diving; and a source of bioactive compounds used in drugs to treat inflammation and certain types of cancer.

“If you look at a photo of coral reefs when I started diving in the 1970s and compare it to today, it makes you want to cry,” she said. “The change is just incredible.”

Although she noted that this study has important observations, more in-depth studies are needed to better understand what is happening to the ecosystem.

“I see species bleaching that have never bleached before, but also others that are showing more resilience,” she said. “There are many variations within genera of animals and symbionts. We need to understand these variations.”

The hope is to continue research into the relationships between coral reefs and the sustainability of symbiotic algae while taking steps to end environmental damage caused by human action, such as overfishing and burning of fossil fuels.

“We can’t stop global warming,” Coffroth said. “But we hope we can slow it down.”