The rapid loss of reef-building corals owing to ocean warming is driving the development of interventions such as coral propagation and restoration, selective breeding and assisted gene flow. Many of these interventions target naturally heat-tolerant individuals to boost climate resilience, but the challenges of quickly and reliably quantifying heat tolerance and identifying thermotolerant individuals have hampered implementation. Here, we used coral bleaching automated stress systems to perform rapid, standardized heat tolerance assays on 229 colonies of Acropora cervicornis across six coral nurseries spanning Florida's Coral Reef, USA. Analysis of heat stress dose–response curves for each colony revealed a broad range in thermal tolerance among individuals (approx. 2.5°C range in F v /F m ED50), with highly reproducible rankings across independent tests ( r = 0.76). Most phenotypic variation occurred within nurseries rather than between them, pointing to a potentially dominant role of fixed genetic effects in setting thermal tolerance and widespread distribution of tolerant individuals throughout the population. The identification of tolerant individuals provides immediately actionable information to optimize nursery and restoration programmes for Florida's threatened staghorn corals. This work further provides a blueprint for future efforts to identify and source thermally tolerant corals for conservation interventions worldwide.

Western Atlantic populations of the staghorn coral Acropora cervicornis have drastically declined over the past few decades. Hence, interest in its ecology and spatial extent has increased. Acroporid corals with indeterminate arborescent growth like A. cervicornis primarily reproduce asexually by fragmentation which can lead to extensive monotypic patches. Since fragmentation is a major component in indeterminate acroporid reproduction, these patches may expand or move over time. Periodic perimeter mapping facilitates comparison of patch areas to determine movement or expansion. A repeatable, lowcost method using a differential GPS carried by a snorkeler was employed to map the perimeter of A. cervicornis patches in southeast Florida. Perimeters were mapped over a three-year period. Patch boundaries were dynamic, expanding in one or more directions. Patch areas increased by up to 7.5 times their original size and moved up to 51 m. Results were corroborated by spatial cluster analyses of in situ live coral cover measurements. Getis-Ord Gi* statistic and Anselin Local Moran's I spatial cluster analyses of live coral cover within an array of in situ monitoring plots indicated that significant high cover clusters moved in the direction of mapped patch perimeter expansion. Expansion was coupled by more than 50% decreases in total live cover. Information gained herein shows that A. cervicornis patches are spatially and temporally dynamic, having implications to long-term permanent transect monitoring studies and framework development. Results may be applicable to other shallow water indeterminate arborescent acroporid coral species.

Corals, specifically the Atlantic staghorn coral, Acropora cervicornis, are under major threat as disturbance events such as storms and disease and predation outbreaks increase in frequency. Since its population declines due to a wide spread disease event in the early 1980s, limited long-term monitoring studies describing the impact of current threats and potential recovery have been completed. The aim of this study was to document the impacts of environmental (tropical storms, increased wind) and biological (disease and predation) threats on A. cervicornis to further understand its population dynamics and potential for recovery. Two high-density A. cervicornis patches (greater than 1 hectare each) were surveyed tri-annually (winter, summer, fall) from 2008-2016. A. cervicornis percent cover, canopy height, census of individuals, and prevalence and occurrence of disease, predation, and bleaching were evaluated within permanent 3.5 m radial plots (n = 27 and 31). Temporal variability was observed in mean percent live cover at both patches and showed an overall loss of tissue. Frequent disturbances such as tropical storms, hurricanes, and disease events, caused increased, prolonged, and widespread mortality. Periods void of disturbance allowed for recovery and growth. Prevalence and occurrence of disease and predation were highly variable between monitoring events. They were also found to be significantly higher on masses (individuals ≥ 1.5 m) than on colonies and during summer surveys (June-August). These data indicate that substantial length of time between major disturbance events is necessary for recovery and growth of this species. The implication of these results is that given the current rates of growth, recruitment, and storm frequency, natural species recovery is unlikely unless large scale issues like climate change and ocean warming, which affect the intensity and frequency of disease and predation, are addressed.

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