Transplantation.

Coral transplantation from healthy to degraded reefs, particularly the relocation of newly settled corals, offers a means to ‘seed’ degraded reefs with healthy micro and macroorganisms that can encourage more healthy associations in nearby organisms (Rinkevich, 2021). This strategy not only replaces lost coral cover, but also introduces genetic and ecological diversity to degraded areas, promoting adaptive capacity. By increasing coral cover, introducing genetic diversity, restoring mutualistic relationships, and supporting ecosystem functions, transplantation can mitigate some effects of coral reef degradation. 

Molecular Mechanisms

At the molecular level, coral transplantation can enhance genetic diversity within degraded reefs, a critical factor for adaptive potential. Levy et al. (2024) demonstrated that transplanted corals from thermally tolerant populations introduced alleles associated with heat resistance into a degraded reef system, increasing the likelihood of survival under future temperature extremes. These findings underscore the importance of selecting donor corals with favorable genotypes, particularly those exhibiting stress-resilient traits, to promote the proliferation of advantageous alleles within local populations. Molecular analyses have also shown that transplanted corals can maintain robust gene expression profiles for heat shock proteins and antioxidant enzymes, which are critical for managing cellular stress (van Oppen et al., 2015).

The Coral Holobiont

Transplanted corals often bring with them a microbiome shaped by the environmental conditions of the donor reef, which can influence their survival and acclimation in the new habitat. Recent studies have demonstrated that transplantation can induce shifts in the coral microbiome, with changes in bacterial community composition linked to the coral's acclimation to new environmental conditions. The introduction of beneficial microbes, such as nitrogen-fixing bacteria and those involved in organic matter recycling, has been shown to improve coral resilience by supporting metabolic functions and mitigating oxidative stress (Peixoto et al., 2017). Levy et al. (2024) demonstrated that corals transplanted from thermally tolerant donor reefs retained a significant proportion of their original symbiont population but also incorporated local symbionts from the degraded reef environment over time. This hybrid symbiont assemblage improved the thermal tolerance of transplanted corals, as the locally acquired symbionts exhibited traits better adapted to the high-stress conditions of the degraded reef. Notably, the introduction of diverse and thermally resilient symbionts enhanced the corals' photosynthetic efficiency and stress resistance, suggesting that transplantation not only restores coral cover but also facilitates the establishment of more resilient holobiont communities. These findings underscore the potential of transplantation as a mechanism for promoting adaptive symbiont shifts, which can be critical for coral survival in warming oceans

Ecosystem Dynamics 

Transplanted corals affect ecosystem dynamics by providing additional genetic and biodiversity, and potentially through poorly understood mechanisms of encouraging other organisms to establish residence in the healthy zones. As these studies are new, long-term survivorship is not known, nor are effects on the assemblages of other organisms that grow in or near the transplanted corals. If the transplants are able to maintain their healthy holobiont through time, it is likely that the effects on surrounding organisms would also be positive, due to the spillover of diverse and healthy microorganisms, as well the habitat structure provided by the corals. 

Strategy

Long-term monitoring of this incredibly promising technique in different ecological regions is essential for advancing our understanding of its effectiveness. Regional areas may also differ in success rates, as there is some risk of disease transmission (Levy et al., 2024), and environmental mismatches between donor and recipient sites (van Oppen et al., 2015). Transplantation is a resource-intensive processes that includes collection, transportation, and monitoring, so scaling will require additional development.