A race is also underway in the US, to save the bleached corals of the Flordia Keys Reef Tract. Florida's coral reef system, which is the third largest in the world, is under severe threat. Now, a novel approach is boosting the survival chances of two of its primary reef-building coral species, both of which are endangered: the pale brown, pointed-antler-like staghorn (Acropora cervicornis) and the flattened-antler-like elkhorn (Acropora palmata). Both the staghorn and the elkhorn have been devastated by disease and climate change, and have seen a 97% decline in their population since the 1970s. The Coral Restoration Foundation (CRF), the world's largest reef restoration organisation, was formed in 2005 in response to this population crash.
CRF operates coral nurseries in the ocean that grow juvenile coral, which are then transplanted to reef restoration sites in an effort to stave off the extinction of coral species and restore balance to the reef ecosystems. The corals are grown on floating, anchored trees made from polyvinyl chloride (PVC) with fibreglass branches onto which coral fragments are attached with thin plastic lines. This structure allows them to grow particularly fast, says Phanor Montoya-Maya, CRF's restoration programme manager. This is because the suspended corals are surrounded by light and waterborne nutrition and are more protected from storms and other disturbances than they would be if they were anchored to the sea floor. According to Montoya-Maya, the corals are "reef-ready" in six to nine months.
CRF's Tavernier Coral Tree Nursery in the Florida Keys covers 1.5 acres (6,070 sq m) of ocean floor, contains more than 500 coral trees, and is capable of producing 40,000 reef-ready corals every year, the organisation says.
Even restored reefs still face the threat of global warming, however. In July 2023, a marine heat wave in Florida caused ocean temperatures to soar: in some areas ocean temperatures exceeded hot tub levels of 100F (37.7C). The bleaching threshold for coral is typically around 87F (30.5C). When water temperatures cross that red line and stay that way for a month or more, coral is stressed to such a degree that it has to expel the algae (zooxanthellae) in its tissues. This algae gives coral both its distinctive color and, in a unique symbiotic relationship, it also feeds vital nutrients to its coral host. Bleached coral can survive and eventually recover, but any recovery requires water temperatures to revert back to a less extreme range and stay that way. This past summer in Florida the heat was so extreme that in some instances the coral tissue began to dissolve, eliminating any prospect of recovery, according to CRF.