Historical temperature variability and past exposure to heat stress have been found in recent studies to be key factors contributing to coral reef resilience. With future heat stress predicted to become more frequent and severe, prioritizing sites with locally higher variability and lower warming trends in historical and predicted temperature may represent the greatest opportunity for success of coral reef restoration activities in the face of climate change. Understanding spatial patterns of thermal history can inform selection of sites for targeted restoration efforts. NOAA Coral Reef Watch (CRW) has recently updated its Thermal History product suite, extending the period for calculating metrics to 1985-2017 and transitioning the source data to use CRW’s CoralTemp dataset. CoralTemp is a global, daily, 0.05° (~5 km) gridded sea surface temperature (SST) product, which has an internally consistent baseline through the entire period and now underpins CRW’s near real-time decision support system for coral bleaching management. The updated Thermal History suite maintains the existing thematic groupings of Stress Frequency, Stress Onset, SST Variability, SST Trend, Climatology, and Annual History, with data and images provided at https://coralreefwatch.noaa.gov/satellite/thermal_history/. Augmenting historical variability, exposure and trends with downscaled future projections of heat stress (at ~4 km resolution, https://coralreefwatch.noaa.gov/climate/projections/downscaled_bleaching_4km/) further provides managers with information to support site selection for restoration efforts. Other physical and anthropogenic site characteristics, such as those recommended in guidance for assessing reef resilience (e.g., light stress, pollution, fishing pressure), will also help guide prioritization of restoration sites.

A major obstacle for reef conservation is the identification of stress tolerant corals and habitats at large scales. We present a novel method to overcome this limitation, detecting tolerant corals using prior information on the natural bleaching response of individual colonies and airborne imaging spectroscopy. The Carnegie Airborne Observatory (CAO) collected high-fidelity spectral data for all hardbottom habitats within Kaneohe Bay, Oahu, Hawaii, an area of approximately 45km2. These data were analyzed via machine learning with prior bleaching observations for Montipora capitata and Porites compressa to classify bleaching phenotype at the coral colony scale. This strategy can discriminate bleaching phenotype using imaging spectroscopy data, even for colonies that show no visual signs of current bleaching or paling. Spectral data can also resolve chlorophyll content and Symbiodinium counts at the organismal level. The capacity to accurately predict species-specific response to thermal stress highlights spatial patterns at landscape scales, including clustering of stress tolerant corals on some reefs and the distribution and margins of species aggregates. These patterns show the importance of the interaction between habitat and the coral holobiont for successful conservation. The capability to detect phenotype from spectral data could be scaled to include entire reef ecosystems or down to hand-held, in situ instruments to achieve similar predictive capabilities where prior data or future monitoring can provide biological context.

Increasing sea surface temperatures and ocean acidification are threatening the long-term survival of corals and the persistence of coral reef ecosystems. The coral microbiome has been identified as a potential factor in the resilience of corals to these changing environmental conditions. Improving our understanding of the relationships between the coral host and their microbial associates under changing ocean conditions could produce innovative approaches to coral reef restoration. Coral reefs surrounding Oahu, Hawai’i, USA exist among a natural gradient of environmental conditions, with some sites experiencing summertime temperature and pCO2 levels not expected to occur in most tropical waters until mid-century. We hypothesize that local variability in seawater temperatures and pCO2 drive coral-associated bacterial community composition, and that these differences are species-specific. To test this, we characterized the bacterial communities of five coral species from six sites around Oahu. Preliminary results from two species suggest that the bacterial community composition differs between Porites compressa and Montipora capitata corals. Additional analyses are underway to determine if differences in the temperature and pCO2 properties among sites further influences the bacterial community composition. The coral microbiome will also be interpreted in the context of physiological parameters of these corals presented in a companion abstract. Overall, characterizing the coral microbiome across a range of environmental conditions can help restoration and protection efforts to target corals better adapted for predicted future ocean conditions.

Guam’s coral reefs were impacted by widespread bleaching during four of the last five years, an extreme frequency that may become ubiquitous due to continued ocean warming. About half of the island’s staghorn Acropora spp. died between 2013 and 2015 as a result of bleaching and extreme low tides. From 2013-2017, four of Guam’s 21 known staghorn populations experienced 100% mortality. The severe, sudden decline of these taxa indicates a need for direct, urgent management interventions, including restoration. Recognizing the challenge of maintaining in situ nurseries and outplants in stressful environments, we are developing science-based protocols for restoration site selection, culturing methods, and outplant techniques to guide local management interventions. As part of this effort, we are evaluating the implications of water flow for restoration success, as high water flow may provide refuge from warming. We used Illumina RNAseq to study the effects of high and low flow regimes on gene expression of Acropora pulchra. We found differential expression of genes potentially related to heat stress in an ex situ experiment, then compared these trends to in situ flow-driven transcriptomic responses under naturally occurring heat stress during a bleaching event. We found differential gene expression between low flow and high flow samples in both ambient (ex situ) and heat-stress conditions (in situ). We compared both low and high flow samples against heat stress samples, and found that high flow samples may be up-regulating stress-related genes at baseline conditions, known as “front loading”. Front loading may be characteristic of resilient corals, as they are better able to respond quickly to stressors. This research has important implications for reef restoration, indicating that in situ coral nurseries and outplanted populations may be more likely to withstand stressors if located at sites with high water flow. Fragments collected from high flow sites or cultured in nurseries with high flow regimes may demonstrate front loading and thus be more resilient. Furthermore, flow rates should be considered when designing nursery structures and selecting outplant methods, as water flow may impact coral resilience and restoration success at small scales.

Ecological restoration of forests, meadows, reefs or other foundational ecosystems in the face of climate change depends on the discovery and use of individuals able to withstand future conditions. For coral reef restoration, finding climate tolerant colonies does not guarantee clonal progeny will remain tolerant in different environments because of widespread environmental adjustment of coral physiology and contributions from internal symbionts. Here, we test if simple proxies of heat tolerance for parent corals are predictive of nursery growth and bleaching tolerance. Before the 2015 natural bleaching event in American Samoa, we set out 800 coral fragments from 80 colonies of four species that had been selected by prior tests to have a range of intraspecific natural heat tolerance. After the event, clones from heat tolerant parents resisted bleaching 20-85% better across species than clones from less tolerant parents and retained higher clonal diversity through the bleaching event than did less heat tolerant corals. The three simplest proxies for thermal tolerance (response to experimental heat stress, location on the reef, and thermal microclimate) predicted the response of nursery clones of all four species to the bleaching event. Molecular biomarkers were also predictive but were highly species specific. Colony genotype explained the most variance in bleaching response (38%), playing a stronger role than the symbiont and demonstrating a key role for individual variation in the restoration process. Combined, our results show that selecting for host resilience produced a multi-species coral nursery that withstood multiple bleaching events and that proxies for thermal tolerance in restoration efforts can be species independent and inexpensive.

Following the decline of the Caribbean Acropora population, recent evidence points toward a natural population increase of a viable reproductive acropora hybrid, Acropora prolifera. To better understand the physiological variability between hybrid genotypes, and its usefulness in restoration ecology, this study aimed to monitor baseline health characteristics between A. prolifera populations and across genotypes within a restoration framework. Reciprocal transplant experiments were conducted between fragments from two geographically distinct offshore islands near St. Thomas, U.S. Virgin Islands. Within each sampled population, three distinct genotypes were identified using molecular analysis. Every month for nine months, health metrics including growth rates, number of new apical tips, and signs of stress including mortality, predation, temperature, and disease were compared between populations and across genotypes. Furthermore, we analyzed the linear relationship between growth rates and thermal conditions in-situ. Using linear mixed effects models, non-natal genotypes showed no significant differences in growth rates compared to natal genotypes. Non-natal genotypes did however, show higher signs of predation than natal genotypes (generalized linear mixed effects model, z = 2.12, p = 0.033). Using linear regressions we observed a positive linear relationship between vertical (β = 0.121, t(263) = 2.15, p = 0.02) and horizontal (β = 0.204, t(263) = 3.01, p < 0.01) growth axes with temperature. Overall, these results show no reduction in health for transplanted A. prolifera fragments to non-natal locations. Furthermore, we observed growth rate trends that are similar to the parental species within optimal temperature ranges. Despite concerns of genetic incompatibilities associated with this hybrid, our study suggests that A. prolifera can be successfully propagated to distinct reefs. The incorporation of the hybrid in a controlled manner with current and future coral restoration programs may benefit restoring Acropora populations throughout the Caribbean and stimulate genetic diversity.

Many factors go into decisions of where and what species to use for restoration, including reef-protection status, presence of live corals, historic coral success, and environmental conditions at sites being considered. We report on a study, started in 2009, measuring coral-calcification rates at six outer-reef tract sites in the Florida Keys, U.S.A. To date, we have measured the growth of Siderastrea siderea, Orbicella sp., Porites astreoides, Acropora cervicornis, and A. palmata by monitoring buoyant weight of corals for two-year periods. Generally, calcification rates were highest at the most remote site in Dry Tortugas National Park compared to the other 5 sites, and partial mortality was highest at sites in the Middle Keys, indicating that local conditions may modulate the success of restoration. Calcification rates on a planar-surface (“canopy”) basis (mg cm-1 day-1) were 1.5 for Orbicella sp., 2.7 for S. siderea, 3.3 for P. astreoides, 4.7 for A. palmata, and 5.8 for A. cervicornis. The estimates for Orbicella sp. and P. astreoides are likely low because of high-temperature stress during the summers of 2014 and 2015, respectively. An additional experiment showed that grow-out methods (“tree” vs. “block”) affect the robustness of A. cervicornis outplants and that there is likely a genetic basis for differential calcification rates. Our study suggests that achieving restoration goals for ecosystem services like shoreline protection and habitat provision requires matching species selection with physical-site considerations, and we suggest shifting more effort to restoring A. palmata.

Florida Keys coral reefs have experienced seven mass bleaching events since 1987. Many reefs have < 5% coral cover, but some inshore patch reefs have maintained significantly higher coral cover. It has been hypothesized that the inshore corals are acclimatized and/or adapted to recurrent heat stress owing to naturally higher and more variable temperatures. The response of Florida Keys coral reefs to back-to-back bleaching events in 2014 and 2015 provided direct evidence of bleaching resilience on the inshore patch reefs. Inshore sites demonstrated better recovery and often higher bleaching resistance than offshore sites. 2015 and 2014 were the two hottest summers on record for the Florida Keys, yet total colony mortality at Cheeca Rocks, an inshore patch reef, was low with 94.7% of > 4000 colonies surviving. There was a reduction in bleaching severity and mortality with the second stronger thermal anomaly in 2015, which suggests that acclimatization may be possible with short recovery. Lab-based experiments have shown that inshore genotypes of the ESA-listed coral Orbicella faveolata exhibit a significantly greater heat tolerance relative to offshore genotypes. This presentation will summarize these findings as well as present preliminary data from a reciprocal transplant experiment that aims to understand if the inshore-offshore dichotomy in heat resistance is due to acclimatization or adaptation. The existence of corals on the inshore patch reefs at temperatures that are +1.0oC warmer than offshore sites in the Florida Keys may be an important source of heat-tolerant genotypes for restoration.

The Elkhorn coral, Acropora palmata, was the primary reef builder in the western Atlantic over the last 2 million years, however, because of recent region-wide declines this species is now threatened and has prompted conservation/restoration specialists to take new actions. Despite its historical abundance throughout the western Atlantic, A. palmata was only sporadically observed in one small area of Dry Tortugas National Park (DRTO) and has been reported as absent from fossil reef deposits at DRTO. A better understanding of the history of A. palmata at DRTO could provide critical insights into the environmental controls on its growth and decline. Using diver surveys and radiometric dating, we present the first record of late Holocene-aged (~4,500–2,750 years ago) A. palmata populations from DRTO. Contrary to reports from previous studies, however, we show that A. palmata populations in DRTO created extensive reef crest habitats during the late Holocene that may have existed continuously for ~1,750 years. The beginning of this timeframe corresponds to a period of warmer temperatures compared to the later Holocene, and the termination of A. palmata by 2,750 years ago is coincident with overall declines in reef-building at DRTO. If cold water was limiting A. palmata at DRTO in the recent past, that limitation could be lifted now with continued ocean warming. Given that DRTO possesses some of the healthiest modern reefs throughout the Florida reef tract, and its isolation from mainland Florida and other direct anthropogenic impacts, we suggest this as an optimal target area for A. palmata restoration, especially since modern populations there are so limited.

The Florida Reef Resilience Program’s Disturbance Response Monitoring program (DRM) was developed to assess stony coral condition on shallow coral reefs from the Dry Tortugas to Martin County during the months of high thermal stress. Results from DRM survey events have shown that bleaching prevalence is variable across time and space. Using in-situ temperature data collected from temperature loggers affixed to the reef, this study will show how bottom water temperature regimes during the thermal stress months from August to October relate to coral bleaching prevalence measured by DRM. This presentation will focus on two subregions of the Florida Keys to pilot a larger study that aims to compare temperature and bleaching prevalence data across the entire Florida reef tract.

Worldwide coral transplantation efforts are being undertaken to restore reefs lost to climate change-induced bleaching and disease. Successful reef restoration efforts to date are limited to shallow depths above 10 meters with fast growing corals, despite the loss of many coral species across a wide range of depths. In this study, we constructed Orbicella faveolata and Orbicella annularis restoration nurseries along a depth gradient to test coral survival and growth capacity at different depths, to facilitate restoration activities at greater depths in the future. We assessed 10 genets of each species at 20 m and 30 m (n=15), using a total of 600 fragments. We identified two genets which we found to be highly successful across depths. We did not find significant differences in coral survival between depths. Out of 300 fragments at each depth, 46% (138 fragments) survived at 30 m, while 52% (158 fragments) survived at 20m. This preliminary study identifies favorable genotypes for future transplantation and emphasizes the importance of genotype selection during transplantation.