In 2023, a record-setting marine heat wave triggered the ninth mass coral bleaching event on Florida’s Coral Reef (FCR). We examined spatial patterns of heat exposure along the ~560-kilometer length of FCR and the mortality of two ecologically important, critically endangered reef-building corals. Sea surface temperatures were ≥31°C for an average of 40.7 days, leading to heat exposures 2.2- to fourfold higher than all prior years on record. In the Florida Keys and Dry Tortugas, 97.8 to 100% of the Acropora palmata and Acropora cervicornis colonies died. Mortality was lower offshore southeast Florida (37.9%), reflecting cooler temperatures in this region. Since the late 1970s, multiple stressors had already reduced the ecological relevance of Acropora in Florida, but the 2023 heat wave marks their functional extinction from FCR.

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.

Coral reefs of Grand Bahama and New Providence islands in The Bahamas have been surveyed several times over the past decade, and long-term monitoring indicates declines in coral cover associated with hurricanes, bleaching events, and local threats. However, the greatest declines in coral populations in The Bahamas over the past decade may be attributed to the recent introduction of stony coral tissue loss disease (SCTLD). In 2019, a comprehensive assessment of both islands was conducted using Atlantic and Gulf Rapid Reef Assessment (AGRRA) methods to characterize reefs before SCTLD was reported in The Bahamas. Following reports of SCTLD in late 2019, timed roving diver assessments of corals were conducted for Grand Bahama in March 2020 and New Providence in June 2020 to determine which species were affected by the disease and the proportion of corals that were healthy, infected with SCTLD, and those that appeared to have experienced recent mortality for the most abundant intermediate or highly susceptible species. Additional surveys were conducted for both islands in January 2021 to further assess the extent of the outbreak, and repeated assessments of several sites for each island were used to determine the impact of the disease on corals over the previous 6.5 to 10.5 months. Infection rates varied among species following patterns described for Florida and elsewhere, with higher infection rates occurring in vulnerable species for both Grand Bahama and New Providence. Pseudodiploria strigosa appears to be the most affected species with 45.6% of colonies on Grand Bahama infected and 23.1% infected on New Providence and recent mortality rates of 31.5 and 42.7%, respectively, at the time of surveys. Spatial patterns of mortality and infection rates for the most vulnerable species were greatest close to international commercial shipping ports on both islands, suggesting SCTLD has been present in those locations for a longer time, and the proportion of healthy colonies increased with distance from the port. For Grand Bahama, there was also a significant effect of depth, with shallow reefs having a higher proportion of colonies that was infected or experienced recent mortality. For New Providence, sites to the east of the port saw a sharp decline in infection and mortality rates with distance compared to sites west of the port, where nearly the entire coastline was affected by SCTLD. Temporal analyses showed an increase in recent mortality and a decrease in active infection for most species on both islands, but little change in the proportion of healthy corals, suggesting some degree of resistance to the disease. Because Freeport and Nassau are the two largest container ports in The Bahamas and are over 200 km apart with multiple islands between them where SCTLD has not yet been reported, it is probable that SCTLD arrived in The Bahamas via commercial shipping, followed by rapid spread within islands via local currents and other vectors. Results from this study stress the need for early detection and suggest that preventing the spread of the disease between islands via vessel traffic is of utmost importance.

An understanding of temporal patterns of migration and spatial connectivity between home ranges and spawning sites is necessary for effective management of species that form transient spawning aggregations. The Nassau Grouper Epinephelus striatus is a Caribbean coral reef fish that displays such spawning aggregations, which have been overfished to the point of threatening the species. Using acoustic telemetry, we examined the size at which Nassau Grouper migrate to spawning aggregations, the timing of migrations, and the distance of migration routes used by Nassau Grouper from within and outside of a large, no-take marine reserve in the central Bahamas. Fish (total n = 19) were tagged in 2004 (n = 6) and 2005 (n = 13) and were tracked for one to four spawning seasons. Fish that were 54 cm TL or greater made spawning migrations, with all but one migrating southward along the shelf edge of Exuma Sound for a distance of 70 km to over 200 km, usually during the December full moon. Fish typically made one migration annually, which lasted from 1 to 3 weeks, with fish remaining at spawning sites for only 1–2 d; however, when the full moon was early in the spawning season, several fish remained away from their home reefs through two lunar cycles or delayed their migrations by a month, and one fish made two migrations. Fish that were migrating for the first time had slower swimming speeds to spawning sites than did experienced fish, but swimming speeds were similar between the two groups during return migrations, suggesting that their migration behavior was learned. Our results demonstrate that spawning migration patterns for this species may be more variable in The Bahamas than at other Caribbean locations. The present findings also have important implications for the management of the species, including increasing the minimum size limit to 54 cm or larger and the use of both marine protected areas and seasonal closures to rebuild the spawning stock. Received February 1, 2016; accepted July 27, 2016