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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.

18Marine heat waves instigated by anthropogenic climate change are causing increasingly frequent 19 and severe coral bleaching events that often lead to widespread coral mortality. While 20 community-wide increases in coral mortality following bleaching events have been documented 21 on reefs around the world, the ecological consequences for conspecific individual colonies 22 exhibiting contrasting phenotypes during thermal stress (e.g. bleached vs. not bleached) are not 23 well understood. Here we describe the ecological outcomes of colonies of the two dominant reef-24 building coral species in Kāne ohe Bay, Hawai i, Montipora capitata and Porites compressa, 25 that exhibited either a bleaching susceptible phenotype (bleached) or resistant phenotype (non-26 bleached) following the second of two consecutive coral bleaching events in Hawai i in 2015. 27Conspecific pairs of adjacent bleaching susceptible vs. resistant corals were tagged on patch 28 reefs in two regions of Kāne ohe Bay with different seawater residence times and terrestrial 29 influence. The ecological consequences (symbiont recovery and mortality) were monitored for 30 two years following the peak of the bleaching event. Bleaching susceptible corals suffered higher 31 partial mortality than bleaching resistant corals of the same species in the first 6 months 32 following thermal stress. Surprisingly, P. compressa had greater resilience following bleaching 33 (faster pigment recovery and lower post-bleaching mortality) than M. capitata, despite having 34 less resistance to bleaching (higher bleaching prevalence and severity). These differences 35 indicate that bleaching susceptibility of a species is not always a good predictor of mortality 36 following a bleaching event. By tracking the fate of individual colonies of resistant and 37 susceptible phenotypes, contrasting ecological consequences of thermal stress were revealed that 38 were undetectable at the population level. Furthermore, this approach revealed individuals that 39 underwent particularly rapid recovery from mortality, including some colonies over a meter in 40 diameter that recovered all live tissue cover from >60% partial mortality within just one year. 41These coral pairs continue to be maintained and monitored in the field, serving as a "living 42 library" for future investigations on the ecology and physiology of coral bleaching. 43 44 45 46 102 2008; Bahr et al., 2017; Hughes et al., 2017). Kāne ohe Bay, Hawai i, located on the northeast 103 coast of O ahu, is an opportune system for investigating this question of how intraspecific 104 variability in coral responses to thermal bleaching events driven by climate change influence 105 coral survival. The two dominant reef-building coral species in the bay, Montipora capitata and 106Porites compressa, both exhibit differences in thermal performance within and between species 107 during bleaching (Grottoli et al., 2006; Cunning et al., 2016; Wall et al., 2019). Differences in 108 5 symbiont associations and nutritional plasticity a...

Coral holobionts are multi-species assemblages, which adds significant complexity to genotype-phenotype connections underlying ecologically important traits like coral bleaching. Small scale heterogeneity in bleaching is ubiquitous in the absence of strong environmental gradients, which provides adaptive variance needed for the long-term persistence of coral reefs. We used RAD-seq, qPCR and LC-MS/MS metabolomics to characterize host genomic variation, symbiont community and biochemical correlates in two bleaching phenotypes of the vertically transmitting coral Montipora capitata. Phenotype was driven by symbiosis state and host genetic variance. We documented 5 gene ontologies that were significantly associated with both the binary bleaching phenotype and symbiont composition, representing functions that confer a phenotype via host-symbiont interactions. We bred these corals and show that symbiont communities were broadly conserved in bulk-crosses, resulting in significantly higher survivorship under temperature stress in juveniles, but not larvae, from tolerant parents. Using a select and re-sequence approach, we document numerous gene ontologies selected by heat stress, some of which (cell signaling, antioxidant activity, pH regulation) have unique selection dynamics in larvae from thermally tolerant parents. These data show that vertically transmitting corals may have an adaptive advantage under climate change if host and symbiont variance interact to influence bleaching phenotype.

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Spatial genetic structure (SGS) is important to a population's ability to adapt to environmental change. For species that reproduce both sexually and asexually, the relative contribution of each reproductive mode has important ecological and evolutionary implications because asexual reproduction can have a strong effect on SGS. Reef building corals reproduce sexually, but many species also propagate asexually under certain conditions. In order to understand SGS and the relative importance of reproductive mode across environmental gradients, we evaluated genetic relatedness in almost 600 colonies of Montipora capitata across 30 environmentally characterized sites in Kaneohe Bay, Oahu, Hawaii using low-depth restriction digest associated sequencing. Clonal colonies were relatively rare overall but influenced SGS. Clones were located significantly closer to one another spatially than average colonies and were more frequent on sites where wave energy was relatively high, suggesting a strong role of mechanical breakage in their formation. Excluding clones, we found no evidence of isolation by distance within sites or across the bay. Several environmental characteristics were significant predictors of the underlying genetic variation (including degree heating weeks, time spent above 30°C, depth, sedimentation rate and wave height); however, they only explained 5% of this genetic variation. Our results show that colony fragmentation contributes to the ecology of M. capitata at local scales and that genetic diversity is maintained despite strong environmental gradients in a highly impacted ecosystem, suggesting potential for broad adaptation or acclimatization in this population.

Reef restoration via direct outplanting of sexually propagated juvenile corals is a key strategy in preserving coral reef ecosystem function in the face of global and local stressors (e.g. ocean warming). To advance our capacity to scale and maximize the efficiency of restoration initiatives, we examined how abiotic conditions (i.e. larval rearing temperature, substrate condition, light intensity, and flow rate) interact to enhance post-settlement survival and growth of sexually propagated juvenile Montipora capitata. Larvae were reared at 3 temperatures (high: 28.9°C, ambient: 27.2°C, low: 24.5°C) for 72 h during larval development, and were subsequently settled on aragonite plugs conditioned in seawater (1 or 10 wk) and raised in different light and flow regimes. These juvenile corals underwent a natural bleaching event in Kāne‘ohe Bay, O‘ahu, Hawai‘i (USA), in summer 2019, allowing us to opportunistically measure bleaching response in addition to survivorship and growth. This study demonstrates how leveraging light and flow can increase the survivorship and growth of juvenile M. capitata. In contrast, larval preconditioning and substrate conditioning had little overall effect on survivorship, growth, or bleaching response. Importantly, there was no optimal combination of abiotic conditions that maximized survival and growth in addition to bleaching tolerances. This study highlights the ability to tailor sexual reproduction for specific restoration goals by addressing knowledge gaps and incorporating practices that could improve resilience in propagated stocks.