Coral bleaching response is unaltered following acclimatization to reefs with distinct environmental conditions

Abstract

Urgent action is needed to prevent the demise of coral reefs as the climate crisis leads to an increasingly warmer and more acidic ocean. Propagating climate change–resistant corals to restore degraded reefs is one promising strategy; however, empirical evidence is needed to determine whether stress resistance is affected by transplantation beyond a coral’s native reef. Here, we assessed the performance of bleaching-resistant individuals of two coral species following reciprocal transplantation between reefs with distinct pH, salinity, dissolved oxygen, sedimentation, and flow dynamics to determine whether heat stress response is altered following coral exposure to novel physicochemical conditions in situ. Critically, transplantation had no influence on coral heat stress responses, indicating that this trait was relatively fixed. In contrast, growth was highly plastic, and native performance was not predictive of performance in the novel environment. Coral metabolic rates and overall fitness were higher at the reef with higher flow, salinity, sedimentation, and diel fluctuations of pH and dissolved oxygen, and did not differ between native and cross-transplanted corals, indicating acclimatization via plasticity within just 3 mo. Conversely, cross-transplants at the second reef had higher fitness than native corals, thus increasing the fitness potential of the recipient population. This experiment was conducted during a nonbleaching year, so the potential benefits to recipient population fitness are likely enhanced during bleaching years. In summary, this study demonstrates that outplanting bleaching-resistant corals is a promising tool for elevating the resistance of coral populations to ocean warming.

Growth and survival among Hawaiian corals outplanted from tanks to an ocean nursery are driven by individual genotype and species differences rather than preconditioning to thermal stress

“…While individual genotypes of some species might be resilient to repeated warming, experimentally subjecting corals to simulated stress events in order to stress harden them to future warming or to select those individuals most likely to be “winners” appears not to be a practical strategy. This conclusion is corroborated by Barott et al (2021) who likewise recently found no alteration of bleaching response among preconditioned corals in a reciprocal transplant experiment in Kāne‘ohe Bay. Taken together, thermally preconditioning or stress hardening corals would likely also not transfer to future generations.…”

“…Examinations of nursery and restored A. cervicornis have suggested the fastest growing genotypes of restored colonies might trade growth for thermal stress recovery ( Ladd et al, 2017 ), a potential tradeoff of skeletal density with branch extension ( Lohr & Patterson, 2017 ), and growth alone when moved from nursery to reef was not predictive of success ( O’Donnell et al, 2018 ). Additionally, based on the outcome of this study and ( Barott et al, 2021 ) the time, effort, and increased expense of thermal preconditioning to promote stress hardening is not warranted.…”

Census of heat tolerance among Florida's threatened staghorn corals finds resilient individuals throughout existing nursery populations

“…Because relatively few genets were shared between nurseries it is hard to generalize from these results. However, reciprocal transplant studies have shown that corals typically maintain similar thermal tolerance even after being moved to a new environment [13,61,62].…”

Horizon scan of rapidly advancing coral restoration approaches for 21st century reef management

“…Following translocation, it is anticipated that transplants interbreed with the native population and that heat tolerance alleles will be incorporated into the native genetic background. Translocation can be achieved with both early life stages or adults, within a reef [28], to a nearby reef [29][30][31] or over larger distances within [32] or between regions [33]. Findings so far suggest transplants largely retain the tolerance ranking exhibited at their native reef site.…”