New guidelines for coral restoration
A bleached reef patch in the Maldives. Rising water temperature causes corals to expel their dinoflagellate symbionts. (Coral Reef Image Bank / XL Catlin Seaview Survey)
Climate change is the greatest threat to the world’s coral reefs. As many reef experts have pointed out, only the strongest and fastest possible action to decrease global greenhouse gas emissions will reduce the risks and limit the impact of related rising temperature, ocean acidification, and sea-level rise on the reefs. Further impact can be minimized by enhancing corals’ resilience through active reef restoration.
Restoration practitioners typically use two approaches to restore damaged or degraded corals: Cloning corals by propagating fragments of adult corals (so-called asexual propagation) or crossing coral gametes to form larvae which each represent new genetic individuals (sexual propagation). The long-term goal of these efforts should be to establish self-sustaining, sexually reproducing coral populations that have sufficient genetic and phenotypic variation to adapt to changing environments.
However, in reality, it is challenging to know how to meet this goal. Therefore, the restoration genetics working group of the Coral Restoration Consortium (CRC) has developed new, concrete guidelines for sourcing and outplanting corals for restoration in the Caribbean, using the best available research and expertise. Those guidelines were outlined in a new paper published today in the journal Ecological Applications.
“The guidelines can be implemented immediately and are grounded in the idea that coral populations can naturally respond to change if they have enough genetic diversity,” said Iliana Baums, Professor of Biology at Pennsylvania State University and chair of the working group that authored the paper. “We are focusing on maintaining or increasing the genetic diversity of coral populations. Having access to greater genetic diversity provides more options for the corals to adapt to their changing environments.”
Nowadays two approaches are used to restore reefs: The photos in the top row show the asexual propagation, coral fragments from adult colonies are used to grow new, clonal colonies and are then replanted on the reef. (Paul Selvaggio) The bottom row shows the larval propagation. Here, coral gametes are collected during spawning night and fertilized so that genetically unique coral embryos develop. Those coral larvae settle on provided substrates and are outplanted onto the reef. (Paul Selvaggio / Reef Patrol / Valérie Chamberland)
Sexual reproduction is key to genetic diversity
Coral populations grow in a variety of environments, covering a range of temperatures, depths, and light conditions, representing a range of local conditions to which they have already successfully adapted. Thus, individuals in different environments should have differences in their genetic code that allow them to thrive in these contrasting environments. In its new paper, the consortium recommends collecting corals for asexual propagation, or coral gametes for sexual propagation, from across these different environments to capture as much genetic diversity as possible.
“Sexual reproduction is key to naturally producing genetic diversity, and rates of sexual reproduction on reefs are dropping dramatically, especially for true reef-building corals. By replanting diverse corals in proximity, the corals can sexually reproduce with each other,” Iliana Baums said. According to the working group, collected corals could be replanted in locations similar to their original environment, or in locations that may soon become similar to their original environment. By taking advantage of improved climate models, scientists and practitioners could anticipate where these traits may be beneficial in the future.
“We really hope that these guidelines will help restoration practitioners in the field to have confidence including ‘weird’ corals from diverse habitats in their restoration activities. Not all of them will be well-suited to new habitats, but some may be and contribute key genes and traits to withstand current and future stressors,” SECORE Research Director Dr. Margaret Miller said, who is a member of CRC’s genetics working group and co-authored the new paper.
Miller, Baums, and their colleagues in the Coral Restoration Consortium are working hard to give coral reefs a fighting chance. “The situation surrounding coral reef decline is certainly dire, but we have a tremendous community of people that is dedicated to solving the problem,” Iliana Baums said. “We have made enormous progress in figuring out how to do coral restoration, and we can make a difference in coral populations today. But for every minute that passes, it gets harder. With every missed opportunity to curb carbon emissions, which contribute to rising ocean temperatures, it gets even harder. Coral reefs are the world’s most diverse ecosystems and they provide incredibly important ecosystem services, so we really cannot afford to lose them.”
Members of CRC's Genetics Working Group, from the left: Mikhail Matz, Carly Kenkel, Sheila Kitchen, Andrew Shantz, Margaret Miller, Iliana Baums, Sarah Davies, John Parkinson – and in the right row: Andréa Grottoli (top), Andrew Baker (middle), and Ilsa Kuffner (bottom). (CRC genetics working group)
About the Coral Restoration Consortium:
The Coral Restoration Consortium was formed in 2016 and established five initial working groups to provide best management practices for coral restoration. Those groups consist of scientists, restoration practitioners, educators, and concerned members of the public. In addition to Iliana Baums and Margaret Miller, members of the Coral Restoration Consortium restoration genetics working group include Sheila Kitchen, Todd LaJeunesse, and Andrew Shantz at Penn State, Andrew Baker at the University of Miami, Sarah Davies at Boston University, Andréa Grottoli at Ohio State University, Carly Kenkel at University of California, Los Angeles, Ilsa Kuffner at the U.S. Geological Survey, Mikhail Matz at the University of Texas at Austin, and John Parkinson, former SECORE research scientist and currently at the University of South Florida.
The paper was published in the journal Ecological Applications:
Iliana Baums et al (2019): Considerations for maximizing the adaptive potential of restored coral populations in the western Atlantic, Ecological Applications. doi.org/10.1002/eap.1978