As temperatures rise and oceans acidify, coral around the globe is being increasingly threatened by the effects of climate change. But for most coral ecosystems, there may be some respite — scientists say that many may be able to migrate poleward to cooler waters as their original habitats become intolerable.
For coral in Florida waters, however, there is no escape.
According to new findings published in the journal Scientific Reports, coral reefs off the southeast coast of Florida are stuck, caught between more frequent cold snaps to the north — the result of rising global temperatures causing a weaker, more wobbly jet stream — and warming water that is getting too hot to be habitable.
“It has been suggested by some scientists that these higher latitudes, more northern latitudes, might be a place where corals could find refuge from climate change,” Lauren Toth, lead author of the study and research scientist at the U.S. Geological Survey’s St. Petersburg Coastal and Marine Science Center, told Grist. “But our research suggests that at least in Florida, and other locations like it, that’s probably not the case.”
Just 2 percent of original Florida coral cover remains today. The rest has been lost in recent years to the effects of climate change, as well as coral disease and runoff of pollution, sediment, sewage, and fertilizer from the state’s rapid population growth and development. Seven of Florida’s coral species are already listed as threatened on the Endangered Species list, including staghorn coral and elkhorn. “Several of the corals that are listed are primarily framework builders,” said Jennifer Moore, a coral recovery coordinator for the National Oceanic and Atmospheric Administration. “They are the ones that have built Caribbean coral reefs over the last 5,000 years.”
Coral reefs play a vital role in southeast Florida: They provide shoreline protection against severe weather events, as well as fuel the state’s tourism and fishing economies. Overall, the state’s reefs have an asset value of $8.5 billion, generate $4.4 billion in local sales, and support 70,000 jobs.
“It’s really that structure of the reef that supports all of those economic functions of reefs,” Toth said.
While some coral species may be able to survive further to the north during warmer seasons, scientists say that entire reef structures won’t be able to be reestablished. “Unfortunately, in a lot of the western Atlantic and Caribbean, the most cold-sensitive corals are also the corals that are responsible for building those long-lasting reef structures,” said Toth. Because climate change is driving more intense temperature swings — with the jet stream dipping further south, bringing cold fronts from the polar vortex with it — coral populations may not live long enough to establish reefs.
“When we get one of these extreme cold snaps, [water temperatures] get down to about 60 degrees Fahrenheit,” Toth explained, “and if that lasts more than a couple of days that’s enough to kill some of these more cold-sensitive corals.”
The researchers said high-latitude reefs in Japan and China may face similar barriers as Florida to migrating poleward.
In Japan, 70 percent of its largest coral reef, the Sekiseishoko reef, is already dead, and at least 90 percent of its corals have experienced some degree of bleaching. Like Florida, the reef is important to Japan for tourism and fishing. China’s reefs have also suffered from warming temperatures. In 2015, a single warming event with an 11-degree Fahrenheit spike in temperature caused 40 percent of coral at the Dongsha Atoll in the South China Sea to die. Both of these reefs sit at high latitudes like Florida’s, and are likely to be constrained by more frequent cold snaps to the north.