Work Begins on Investigation into Coral Resilience Against Climate Warming

In early August, four researchers representing three international scientific and education institutions converged at BIOS to begin field and experimental work for an investigation into coral resilience. Funded by a grant from the Heising-Simons Foundation International, Ltd., this research will build on the results of a previous project, supported by the same donor, that highlighted the importance of environmental history in long-term coral survival.

Among the many threats facing the world’s coral populations are rising ocean temperatures, including short-term, but acute, heating events known as “marine heatwaves.” These regional events are defined by five or more days of water temperatures above the 90th percentile for an area’s historical conditions. Depending on the duration and severity of the heatwave, it can cause a breakdown in the relationship between corals and their symbiotic algae—zooxanthellae—resulting in coral bleaching.

“With our current scientific understanding, it appears that after thermal stress events, such as marine heatwaves, there are ‘winners’ and ‘losers’ in terms of coral species that are able to survive, recover, and transfer long-term resilience to their offspring on a genetic level,” said BIOS marine ecologist and associate scientist Samantha de Putron.

She was joined in August by fellow BIOS faculty member and marine benthic ecologist Yvonne Sawall; coral molecular ecologist Gretchen Goodbody-Gringley, director of research at the Central Caribbean Marine Institute (CCMI); and marine ecophysiologist Hollie Putnam, associate professor at the University of Rhode Island (URI). For two weeks the team engaged in long-term planning for the three-year project, as well as initial research activities designed to help address the project’s central questions: “What natural capacity do corals have to respond to marine heatwaves?” and “Can we use human interventions to enhance corals’ tolerance to heat?”

Corals in Crisis: Can We Extend Their Breaking Point?

The first phase of the project was a short-term “stress test” for corals. This involved measuring the physiological responses (changes in photosynthesis and respiration) and molecular mechanisms of four dominant coral species in Bermuda to acute changes in temperature. Daque Davis, 19, a second-year student at Bermuda College and 2022 BIOS Bermuda Program intern, and Ellie Dunleavy, 20, a second-year student at Penn State University and 2022 BIOS research intern, both participated in this project as part of their summer internships.

“By stress testing the dominant corals and measuring both the host and symbiont [zooxanthellae] responses, we will have a better idea of what is contributing to the resistance and resilience of these species,” Putnam said.

Then, beginning in late September, a longer-term heat stress experiment was implemented with the same species of coral. During this portion of the experiment, which lasted three to four weeks, multiple physiological measurements were recorded and tissue samples were collected for molecular analysis.

“The idea is not to kill the corals, but to expose them to increasing heat loads until signs of stress, such as bleaching, are evident,” Sawall said.

The September to October heat stress experiment is also supporting four interns participating in BIOS’s National Science Foundation Research Experiences for Undergraduates (REU) program. The annual fall internship program, now in its 31st year, pairs U.S. undergraduate students with faculty and research staff for 12-week independent research projects. For the 2022 BIOS REU program, de Putron leveraged the grant-funded investigation to provide hands-on research opportunities structured around the theme of coral larval settlement and recruitment dynamics.

Later in the project, the short-term responses measured in August will be compared to the longer-term responses from September and October to see if coral species that show a strong response and/or resilience to acute temperature changes also show a strong response and/or resilience to longer-term temperature stress. Physiological measurements will then be related to genetic data (DNA) to determine if there are underlying molecular mechanisms of thermal tolerance.

The final phase of the project’s first year will involve monitoring how well the corals recover from heat stress and exploring whether they developed resilience or “carry a legacy” as Sawall puts it.

Looking further down the road, the team is seeking to hire a postdoc beginning spring 2023 to assist with experimental work and overall project management.

Inspiring Future Female Scientists

Also providing research capacity for the investigation is integrative biologist Cali Grincavitch, who has been working with the team since August. Grincavitch was a 2020 BIOS REU intern while she was an undergraduate student at Harvard University. In 2021, she received the Women in Ocean Science Award from CCMI, which allowed her to spend three months in Little Cayman conducting fieldwork in support of the Institute’s research programs. Currently, she is back at BIOS working as a teaching assistant for the 2022 BIOS REU program, which allows her to continue contributing to the grant-funded project by supporting REU interns and mentors de Putron and Sawall.

“Working alongside and learning from four influential women in coral reef ecology is incredibly humbling and inspirational, to say the least,” Grincavitch said. “I am so grateful to be back at BIOS contributing to this research effort, as I firmly believe that investigating corals’ thermal tolerance is a key strategy for building more resilient reefs. Learning how we can best utilize the corals’ existing responses to heat stress starts with fully understanding these mechanisms. I cannot think of a more dedicated team of scientists to lead the way in finding these answers and I am so excited to continue working on this project with them.”