Corals, with their calcium carbonate skeletons and symbiotic photosynthetic algae, are among the first organisms to be negatively impacted by climate change. Warming waters cause coral to expel the algae, called zooxanthellae, while a gradually acidifying ocean, resulting from increased amounts of atmospheric carbon dioxide dissolved in the seawater, can weaken and even dissolve coral skeletons.
Scientists are increasingly concerned with understanding how corals will respond to changing environmental conditions. Specifically, they are interested in the capacity of individual coral species to adapt, acclimatize, and adjust to warming waters.
With funding from Pembroke Foundation International, Ltd., a team of scientists from BIOS and the University of Rhode Island (URI) is investigating these questions using a newly constructed facility at BIOS. Faculty members Samantha de Putron, a marine biologist and ecologist, and Gretchen Goodbody-Gringley, a reef ecologist and evolutionary biologist, are collaborating with Hollie Putnam, a marine ecophysiologist at URI, on a three-year investigation that combines experimental studies with molecular analyses to provide insight into coral resilience.
The study has three specific research goals: to document patterns of natural variation in corals and their larvae among different reef habitats in Bermuda, and to determine if this variation is due to genetics or environmental conditions; to determine if corals residing in certain reef habitats maintain a higher capacity to adapt to environmental conditions and stressors; and to assess how transplantation to different reef environments will affect the ecology and physiology of these corals and their larvae.
“Overall, this research provides insight into processes that may allow subsequent generations of corals to be more adapted to the environmental stressors experienced by their parents,” de Putron said.
Construction of the new facility, called a “mesocosm,” was completed over the course of six months during the spring and summer of 2018. The mesocosm is essentially a large, outdoor experimental aquarium, comprising four large tanks (317 gallon, or 1,200 liter) and eight small tanks (106 gallon, or 400 liter) housed under a removable canopy. The tanks are located adjacent to a small laboratory for on-site experimentation and analyses.
Unlike traditional aquaria that rely on labor-intensive water changes to keep corals healthy, the mesocosm tanks feature a “flow-through” system that pumps seawater from the nearby ocean through a filtration system and into a large reservoir that ultimately supplies each tank with fresh seawater. The team can study corals’ responses to changing conditions within the four larger tanks, where they have the ability to adjust and maintain water temperature, light availability, and the rate of water flow. These capacities are crucial, as they allow researchers to expose corals to a variety of environmental conditions to replicate potential climate change scenarios.
“The ability to mimic environmental conditions from various habitats in this new land-based facility will broaden the scope of the types of research we can achieve at BIOS,” Goodbody-Gringley said.
Over the summer, the team continued coral transplant experiments, which began last year, to determine the effects of parental history (the environmental conditions in which the parent corals grew) on both adult and larval physiology. They also wanted to see how larvae collected from a variety of reef zones—each with different depths, ambient temperatures, wave energy, and light—would respond to conditions of increased temperature, known as “thermal stress.”
To achieve this, corals were collected from two different shallow reef sites on the Bermuda platform and brought back to BIOS, where half were exposed to thermal stress in the experimental tanks. Following a one-month incubation period, the corals were cross transplanted back into the marine environment, where they stayed for roughly one year before scientists returned them to the lab for spawning (larval release) and subsequent analyses of both parent colonies and larvae. Afterward, the corals were transported to the newly-completed mesocosm for a recovery period before they were placed back in the marine environment.
In 2019, the team will expand the coral transplant experiments to include corals collected from both shallow and deep-water sites. They will also begin the molecular portion of their three-year investigation, which includes assessing the rates at which the corals self-fertilize, as well as how genes are expressed in response to environmental changes. Information gained from these mesocosm experiments will help scientists better understand how corals adapt, both individually and across generations, to increased thermal stress in the ocean.
In its first few months of operation, the mesocosm facilty has also supported a variety of other research and education activities. Katelyn Gould, a graduate student at the University of North Carolina at Chapel Hill, is currently working with Goodbody-Gringley on a related investigation into the thermal tolerances of shallow and deep-water corals. Throughout the early fall, Emily Andrew, a BIOS Bermuda Program intern, worked with de Putron looking at the larval ecology of mustard hill coral. She also grew coral fragments in the mesocosm for a long-term study of coral growth rates, which is being used as an experiential learning opportunity for visiting education groups at BIOS.
“These ancillary projects further highlight BIOS’s increased research and education capacity resulting from the new mesocosm facility,” de Putron said.