Heat-driven functional extinction of Caribbean Acropora corals from Florida's Coral Reef.

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. Editor's summary: As little as a 2°C increase in temperature is enough for many corals to bleach, a process in which symbionts are shed and from which recovery is uncertain. An increase of more than a couple of degrees kills corals, and their reef-building skeletons start to crumble. Manzello et al. have been tracking the fate of species of Acropora corals along the Florida Keys. These species have been struggling to survive elevated temperatures for many years, and there have been intensive conservation efforts to restore Acropora spp. reefs. Unfortunately, in 2023, an acute heating event, when water temperatures exceeded the maximum monthly mean sea surface temperature by 2.5°C for many weeks, led to the extinction of wild and replanted corals on the Florida Keys. —Caroline Ash [ABSTRACT FROM AUTHOR]