As climate change and coral bleaching become more severe, it becomes increasingly important to identify and safeguard areas that serve as refugia from thermal stress for coral reef conservation. Drawing on 30 years of research focused on identifying climate refugia, this study calls for a shift in coral reef conservation strategies to more effectively tackle the challenges posed by climate change.
Refugia are sites where biodiversity can retreat to, persist in, and potentially expand from as environmental conditions shift. They fall into three categories:
- Avoidance refugia: areas that avoid physical exposure
- Resistance refugia: areas with low sensitivity to climate change
- Recovery refugia: areas that can quickly recover after exposure
The authors found that most current refugia identified for coral reefs are Avoidance refugia. This is partly due to the heavy reliance on large-scale thermal metrics, such as Degree Heating Weeks (DHW), to predict bleaching events. The overreliance on Avoidance refugia is problematic, particularly as thermal heat waves become more frequent and severe. If these low-heat areas are eventually compromised, the risk of coral loss increases. Therefore, the authors advocate that conservation efforts should also focus on identifying and protecting refugia that display resistance to prolonged heat exposure and the ability to recover swiftly from thermal stress.
To address this, the study recommends using additional metrics beyond DHW. DHW-based models often fail to accurately predict reef outcomes, such as coral cover and recruitment, because they do not account for the varied responses to environmental changes among the diverse reef habitats, species, life histories, and communities. Many alternative environmental (e.g. dissolved oxygen concentrations, calcium carbonate levels, turbidity, nutrient levels, and sedimentation rates), ecological, and life-history variables could be used to measure coral resilience to thermal stress and identify other types of refugia that lead to a diversified portfolio for coral reef conservation.
To create a more effective conservation strategy, the authors highlight the need for a better understanding of coral resistance and recovery dynamics at local scales, the use of a broader range of environmental metrics, and more empirical testing of models against field data on coral cover and community composition.
Implications for managers
- Prioritize safeguarding areas identified as refugia by addressing threats such as overfishing, pollution, disease, and dredging.
- Use environmental and ecological criteria to select sites that include a mix of Avoidance, Resistance, and Recovery refugia.
- Maintain Avoidance refugia as a core component of your strategy, but review and update the criteria or metrics used to identify these areas.
- Collaborate with locally knowledgeable people to validate that proposed refugia align with their local knowledge.
- Build the capacity of practitioners to identify and monitor coral reef refugia.
- Factor in political support and the feasibility of management actions when making decisions about refugia.
- Be prepared to adjust strategies in response to evolving global and local stressors. Learn from past failures and continuously update your approaches using a combination of environmental data and field surveys.
- Continuously improve the definition and mapping of refugia based on new lessons and emerging data.
Author: McClanahan, T.R., E.S. Darling, M. Beger, H.E. Fox, H.S. Grantham, S.D. Jupiter, C.A. Logan, E. Mcleod, L.C. McManus, R.M. Oddenyo, G.S. Surya, A.S. Wenger, J. Zinke and J.M. Maina
Year: 2023
Conservation Biology 38:e14108. doi: 10.1111/cobi.14108
