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

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 Fv/Fm 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.

Fish predation hinders the success of coral restoration efforts using fragmented massive corals.

As coral reefs continue to decline globally, coral restoration practitioners have explored various approaches to return coral cover and diversity to decimated reefs. While branching coral species have long been the focus of restoration efforts, the recent development of the microfragmentation coral propagation technique has made it possible to incorporate massive coral species into restoration efforts. Microfragmentation (i.e., the process of cutting large donor colonies into small fragments that grow fast) has yielded promising early results. Still, best practices for outplanting fragmented corals of massive morphologies are continuing to be developed and modified to maximize survivorship. Here, we compared outplant success among four species of massive corals (Orbicella faveolata, Montastraea cavernosa, Pseudodiploria clivosa, and P. strigosa) in Southeast Florida, US. Within the first week following coral deployment, predation impacts by fish on the small (<5 cm2) outplanted colonies resulted in both the complete removal of colonies and significant tissue damage, as evidenced by bite marks. In our study, 8-27% of fragments from four species were removed by fish within one week, with removal rates slowing down over time. Of the corals that remained after one week, over 9% showed signs of fish predation. Our findings showed that predation by corallivorous fish taxa like butterflyfishes (Chaetodontidae), parrotfishes (Scaridae), and damselfishes (Pomacentridae) is a major threat to coral outplants, and that susceptibility varied significantly among coral species and outplanting method. Moreover, we identify factors that reduce predation impacts such as: (1) using cement instead of glue to attach corals, (2) elevating fragments off the substrate, and (3) limiting the amount of skeleton exposed at the time of outplanting. These strategies are essential to maximizing the efficiency of outplanting techniques and enhancing the impact of reef restoration.

Regional coral disease outbreak overwhelms impacts from a local dredge project.

A repeated-measures coral monitoring program established as part of the PortMiami expansion program provided an unparalleled opportunity to quantify the levels of coral mortality that resulted from both local dredging stress and as a result of climate-related bleaching stress and the subsequent outbreak of a white-plague-like disease (WPD) epizootic. By comparing measured rates of coral mortality at 30 sites throughout Miami-Dade County to predicted mortality levels from three different coral mortality scenarios, we were able to evaluate the most likely source of coral mortality at both the local and regional levels during the 2014-2016 coral bleaching and WPD event. These include scenarios that assume (1) local dredging increases coral disease mortality, (2) regional climate-related stress is the proximal driver of coral disease mortality, and (3) local and regional stressors are both responsible for coral disease mortality. Our results show that species-specific susceptibility to disease is the determining factor in 93.3% of coral mortality evaluated throughout Miami-Dade County, whereas local dredging stress only accurately predicted coral mortality levels 6.7% of the time. None of the monitoring locations adjacent to the PortMiami expansion had levels of coral mortality that exceeded predictions when coral community composition was taken into account. The novel result of this analysis is that climate-mediated coral disease mortality was more than an order of magnitude (14x) more deadly than even the largest marine construction project performed in the USA, and that until climate change is addressed, it is likely that local attempts to manage coral resilience will continue to fail.