‘Thermal Wimps’: Florida Cold Snap Freezes Corals to Death

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Published on February 4th, 2010  |  Discuss This Article  

Meaghan Johnson is a marine science coordinator for The Nature Conservancy in Florida.

A week of record low temperatures recently in South Florida forced us to trade in our flip flops, dig out our sweaters and huddle around our space heaters. For those of you who have ever visited south Florida, you know that this is not part of a common routine – not for people, and not for the coral reefs off Florida’s coasts, either.

In early January, water temperatures in Florida dropped into the frigid upper 40s and lower 50s in some parts of the Keys, far below typical lows of the upper 60s and lower 70s. Not since 1977 when it snowed in Miami has something like this occurred. As reports of fish kills increased, we quickly realized that the cold water was likely having a drastic effect on our corals as well.

Our partners from Mote Marine Laboratory and the Florida Fish and Wildlife Commission were on the water within a week of the cold snap with early reports of recent coral mortality and bleaching occurring in the nearshore waters. We quickly trailered our boat to the Conservancy’s Upper Keys coral restoration sites to check on the corals, do some initial bleaching surveys and download our temperature logger data to see what we were dealing with.

Our first dive was at our deepest forereef site in 50 feet of water, and everything looked normal. With a sigh of relief, we then dove our offshore and mid-channel sites. But as we moved inshore, the percent of recent mortality increased, just as our partners had said. When we reached our in-shore site in 12 feet of water, my heart sunk as I dove down on the lifeless skeletons of what was once a beautiful patch reef teaming with life. The water was cold, the corals were stark white, and parrotfish laid lifeless on the bottom of the reef. I knew instantly that we had to do something to quickly document this rare and unfortunate event.

Our team organized an emergency call to the network of scientist divers who are part of our Florida Reef Resilience Program (FRRP).  This team of scientists monitors the reef annually from the St. Lucie Inlet to the Dry Tortugas over an eight-week period during summer peak-bleaching temperatures. However, these surveys are also designed to be used for disturbances such as this one. Over the next two weeks, this team will monitor the reefs to determine the extent of the cold water damage.

The vulnerability of Florida’s reefs hit us hard, reminding many of us not here in 1977 that the sensitivity of our reef tract extends to cold, not just the rising sea temperatures associated with climate change. Our reef is right on the timberline — the northern edge of the range for shallow coral reef growth — precisely because it is cold here, relatively speaking. We are already at the northern end of where corals, mangroves and other warm-water species can survive, and this cold snap was a good reminder of that fact.

I discussed the delicate balance that corals need to survive with my Conservancy colleague, Mark Spalding. Last year he participated in an emergency coral reef meeting assembled by the Royal Society in London. “Corals are adapted to a tropical world where summer and winter are pretty similar in terms of temperature — they don’t cope with too hot or too cold,” explained Mark. “In lay terms, they are thermal wimps.”

“So this event in Florida shows us very clearly why we can’t hope for coral reefs to simply migrate to slightly cooler waters as climate change digs in,” Mark continued. “They might find things just right in autumn and spring, but they’ll be unbearable in summer AND winter.”

The fragile nature of our reefs makes it all the more important to take care of what we have and remove the stresses. Not only do corals have drastic temperature changes to worry about, but rising CO2 levels in oceans also affect them. Florida’s coral reefs are the only barrier reef in the continental United States, third largest in the world. Not only are the reefs critical to fish diversity, habitat for thousands of fish species, but reef-related expenditures generate more than $4.4 billion annually in southeast Florida and reef recreation supports more than 70,000 jobs.

Have we lost all hope in saving coral reefs in Florida? No. As tragic as this cold event might turn out to be, it reinforces the importance of having a plan in place to protect rare coral reef ecosystems and for understanding their resilience.

The FRRP is a collaborative effort including various agencies and organizations to better understand the ability of Florida’s reefs to withstand climate change and other more localized stresses. Determining where the survivors are, the sturdy corals that withstand stresses, and what gives them an advantage helps managers save these ecosystems. These divers will be able to assess this mortality before algae moves into the dead corals, making species identification difficult and cause-of-death determination impossible.

If you’re interested in coral reefs, check out FRRP’s website. The Nature Conservancy has Reef Resilience programs in other parts of the world as well.

We are counting our blessings at the moment that more coral reefs weren’t damaged in the recent freeze. While there will be coral that we cannot save, there will be many lessons learned from this that will help us in protecting corals in the future.

(Image: Meaghan Johnson diving among coral bleached by the January freeze. Image credit: TNC.)

Opinions expressed here and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy. For more information about our editorial policy and legal terms of use, see our About This Blog page.

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