Assessing the potential for demographic restoration and assisted evolution to build climate resilience in coral reefs

Abstract

Interest is growing in developing conservation strategies to restore and maintain coral reef ecosystems in the face of mounting anthropogenic stressors, particularly climate warming and associated mass bleaching events. One such approach is to propagate coral colonies ex situ and transplant them to degraded reef areas to augment habitat for reef-dependent fauna, prevent colonization from spatial competitors, and enhance coral reproductive output. In addition to such "demographic restoration" efforts, manipulating the thermal tolerance of outplanted colonies through assisted relocation, selective breeding, or genetic engineering is being considered for enhancing rates of evolutionary adaptation to warming. Although research into such "assisted evolution" strategies has been growing, their expected performance remains unclear.We evaluated the potential outcomes of demographic restoration and assisted evolution in climate change scenarios using an eco-evolutionary simulation model. We found that supplementing reefs with pre-existing genotypes (demographic restoration) offers little climate resilience benefits unless input levels are large and maintained for centuries. Supplementation with thermally resistant colonies was successful at improving coral cover at lower input levels, but only if maintained for at least a century. Overall, we found that, although demographic restoration and assisted evolution have the potential to improve long-term coral cover, both approaches had a limited impact in preventing severe declines under climate change scenarios. Conversely, with sufficient natural genetic variance and time, corals could readily adapt to warming temperatures, suggesting that restoration approaches focused on building genetic variance may outperform those based solely on introducing heat-tolerant genotypes. K E Y W O R D S assisted evolution, climate change, coral bleaching, coral reef restoration, evolutionary rescue † Contributed equally as lead authors.

Small‐scale genetic structure of coral populations in Palau based on whole mitochondrial genomes: Implications for future coral resilience

“…Such small‐scale patterns could be generated by low larval movement and also by selection for larvae produced by local parents. These processes have been incorporated into recent models of coral adaptation in the face of climate change (e.g., DeFilippo et al, 2022 ; McManus et al, 2020 ) but such data are not often collected in traditional analyses of coral population genetics (Sheets et al, 2018 ).…”

“…Matz et al ( 2020 ) developed an Indo‐West Pacific model of adaptation based on the migration models of Treml et al ( 2012 ) and showed the possibility of long‐term adaptation across ocean‐wide environmental gradients. At a more local level, McManus et al ( 2020 ) and DeFilippo et al ( 2022 ) used stepping stone models with about 20% recruitment back to the natal reef and showed that wider dispersal spreads locally adaptive alleles but slows potential local increases in adaptive traits such as heat resistance. These models suggest a critical importance of the spatial scales over which natural selection increases allele frequencies to generate successful response to climate (Matz et al, 2020 ), and the scales over which assisted gene flow to accelerate that response will be most valuable (McManus et al, 2020 ; Quigley et al, 2019 ).…”

“…Reef building corals have been a focus of increasing restoration efforts because they are affected so profoundly by ocean warming stemming from climate change (e.g., Hughes et al, 2018 ), in addition to many other anthropogenic disturbances (e.g., Richmond et al, 2018 ). To address these mounting concerns, a suite of approaches has been suggested for interventions to increase climate resilience in corals (reviewed in National Academies of Sciences, Engineering, and Medicine, 2018 ), including using assisted gene flow to support local populations by adding climate adaptive alleles (Cunning et al, 2021 ; Drury & Lirman, 2021 ; Matz et al, 2020 ; Van Oppen et al, 2015 ) and protecting reefs with particular thermal and population traits to further population adaptation (DeFilippo et al, 2022 ; Palumbi et al, 2014 ).…”

Culturing for conservation: the need for timely investments in reef aquaculture

“…Indeed, for some coral species with limited environmental tolerances, aquaculture may serve as a critical tool for their preservation in aquariums and land-based facilities (Schopmeyer et al, 2012;Zoccola et al, 2020). Thus, while the culture of corals has contributed to reef restoration and been used to prevent loss of certain species, little is known about its efficacy when used with a range of coral species and at larger spatial scales, especially with respect to how aquaculture methods may be used to contribute to reef resilience (DeFilippo et al, 2022;Shaver et al, 2022).…”

Microbiomes of a disease-resistant genotype of Acropora cervicornis are resistant to acute, but not chronic, nutrient enrichment

“…However, long-term survival of restored corals is predicted to be low if environmental stressors are not alleviated 9 . Outplanting efforts that do not consider integrating coral resistance and resilience to future stressors will therefore produce communities with low likelihood of future survival 10 , 11 .…”