"Cold Snap" Decimates Florida Livestock and Ancient Corals

Diver observes a recently dead coral head at an Upper Keys inshore patch reef. Right: Transplanted Staghorn Coral was unable to withstand the severe cold temperatures. Photographs: The Nature Conservancy/NOAA.

With cold-stunned iguanas falling dead out of their trees, torpid pythons emerging from hiding to seek the warmth of the sun, and ice on the sidewalks of the town of Frostproof in the heart of citrus country, a prolonged “cold snap” has dealt Florida’s tropical flora and fauna, including many inshore coral reefs, one of its most sustained weather hits in living memory.

When January nighttime temperatures dropped below 30ºF (-1ºC) in south Florida, and water temperatures plummeted below 50ºF (10ºC), reports began to emerge of mass die offs of ocean fish, including snook, tarpon, grunt, snappers, pilchards, Goliath Groupers (below), and moray eels. Estimates of fish deaths run well into the millions in Florida and Whitewater Bays in the Everglades, according to Audubon of Florida.

Hundreds of sea turtles have been rescued from the frigid waters, while dozens of manatees died and hundreds of others congregated in the warmer waters near deep springs and power plants.

In addition to the unseasonal cold air temperatures, high winds from the north worked to push cold, heaver water from the shallows into deeper channels where fishes would normally find warmth and safety. The full impact of the event on Florida’s fish populations is still unknown, and some predict a second wave of deaths as survivors succumb to diseases triggered by stress and weakened immune systems. Seasoned fishing guides are calling the fish kill “utterly devastating,” with populations of mature breeders as well as juveniles and fry of a number of species decimated.Manatees congregating near warm freshwater springs. Photograph by Matthew L. Wittenrich.

Cold Culling the Exotics
Some biologists have cheered the consequences of the extended cold weather, noting that invasive tropical species have been dealt an especially severe blow.

“I’m dancing a jig here,” William Loftus, a retired Everglades National Park ecologist told The Miami Herald. Loftus is now a consultant working on the control of exotic aquatic species. Among the invasives that have settled into Florida waters are  pacu, walking catfish, Tilapia, various large cichlids, including Oscars, piranha, Asian swamp eels, and others.

Anecdotal reports suggest that many exotics are either belly up or dead on the bottom, but the actual fatality rates among these species remains to be determined. Some biologists are also hopeful that invasive aquatic weeds such as water hyacinth, water lettuce, and hydrilla may also have been dealt a severe setback.

Down on the Farm

Not so joyful are the tropical fish farmers and collectors who make up Florida’s ornamental aquaculture industry.  “People are still assessing the damages,” says Scott Moore of Segrest Farms, a leading supplier of tropical fish to the North American pet market. “They’re draining ponds to find out what they have left and trying to rebuild and using the survivors as breeding stock.”  Moore expects it will take “many months, at the least” for the aquaculture industry to rebound.

“Many of us are not set up for one of these once-in-a-hundred-years events,” says Ken Nedimyer of Key Largo, for many years a well-known marine collector and now a reef restoration expert and stony coral nurseryman. (See his CORAL Interview, November/December, 2009). Unknown quantities of marine livestock in holding tanks were lost, as temperatures dropped into the 40ºF range for about 10 days in January in the Upper Florida Keys. “It’s been a really, really tough year for anyone whose living is tied to the aquatic life.”

Emerald Crabs were largely wiped out in shallow, inshore areas.
“Not many people have wanted to go into the water,” but once they do, they are going to find that many inshore reefs are dead. Hundred-year-old, two-hundred-year-old massive coral colonies are dead. They are not just bleached, they are dead. The inshore patch reefs in the Upper and Middle Keys are a wasteland. Most of the sponges (including big barrel sponges), brain corals, Montastrea corals, and gorgonians are dead. In some places, I’d estimate that 75 to 80 percent of the reef is gone.

“Further out from shore and further south, things gradually get better. You might not notice much damage in the Lower Keys, but here there are not many signs of life on the shallow reefs.  The inshore crabs seemed to be wiped out, and you see very few fish.” Nedimyer says that the fish kill was astonishing, with “everything from snappers to barricuda and sharks” washing ashore.

Marine biologist Matthew Wittenrich, at Florida Institute of Technology, says water temperatures off Melbourne fell as low as 41ºF and that the “bulldozer effect” of cold water sweeping Florida’s coastal shallows also resulted in the deaths of many hard-bottom organisms, including Emerald Crabs, above, and other Mithrax crabs. “Collectors told me the crabs seemed to be wiped out, but only a few short weeks later and with a huge recruitment pulse, they are repopulating the habitat. The generation time for many of these organisms is amazingly fast, and it will be fascinating to watch how things recover.”

Nursery Lessons
Nedimyer says his own extensive underwater plots of cultivated stony corals did not emerge unscathed, with an estimated loss of about 30 percent of his frags and small colonies.

“Fortunately, we have surviving colonies from some reef areas that have now lost all their corals.  We should be able to replant them, and they should be able to recover. If it weren’t for having these growing in a nursery, the genetic materials from some of the reefs would have been lost forever.”

Nedimyer, left, reports that Coral Restoration’s “line nurseries,” with stony coral fragments suspended from monofilament lines at various depths had virtually no losses. He said that, during the peak of the cold snap, the layer of water at the bottom was an "unbelievably cold" 53ºF (12ºC), while 5-6 feet above the bottom, he found “warm, blue water.” He adds that the Gulf Stream, which normally keeps south Florida’s waters at a minimum of 77ºF (25ºC) during the winter months had shifted too far from shore to be of much help.

NOAA biologists are assessing the damage and have been surveying reefs from the Dry Tortugas north to Martin County. “The Keys have not seen a cold-water bleaching event like this since the winter of 1977-78, when acres of staghorn coral perished," said Dr. Billy Causey, southeast regional director of NOAA’s Office of National Marine Sanctuaries. "But today we are better prepared to document and assess the impacts of stress thanks to numerous partners.”

“It was a freak thing, and we just have to say, ‘OK, we have some lessons learned,’” says Nedimyer. For example, different phenotypes among his Acropora cervicornis and A. palmata stock showed dramatically different abilities to withstand temperature stock.
Dead Barrel Sponge off Key Largo, February 2010. Photo by Ken Nedimyer.

Dead Star Coral head. Photo by Ken Nedimyer.
Dead Brain and Star Corals. Photo by Ken Nedimyer.

“Some strains were completely wiped out, while others had 100-percent survival. We will be using the survivors for restocking the inshore reefs, and we will be very interested to see if the phenotypes that are cold-resistant are also able to handle warm water better.”

“Some people will ask, ‘Why replant these corals when they are sure to get wiped out again in 50 or a hundred years?’ We know that we can get corals growing again, and that the corals are necessary to support fish and invertebrate populations.  It’s something I think we just have to do.”

Sources
http://coralreef.noaa.gov/
http://www.coralrestoration.org
http://www.nature.org/pressroom/press/press4368.html
CORAL Interview: Ken Nedimyer