Extreme Weather Stresses Ecosystems

By Matthew Cimitile

The freezes in Tampa Bay provide a stark illustration of how extreme weather conditions last winter can greatly stress ecosystems and resources. El Nino combined with a negative Arctic Oscillation weather system and brought frigid winter air to central North America, blasting the Sunshine State with an unprecedented cold spell that lasted 11 consecutive days with temperatures below 34 degrees. The result: millions of dead fish, close to 500 manatee deaths, bleached corals, frostbitten mangroves, more than 65 sinkholes and hundreds of dry wells.

Photos courtesy USGS

Thousands of fish, including large number of snook, washed in from the Gulf of Mexico. Manatees also suffered during the cold snap with nearly 500 deaths attributed to low temperatures.

Tampa Bay lies on an approximate boundary between subtropical and tropical climates. Tropical species like mangroves and manatees do not drift far past the region. Further north, subtropical species are less likely to be impacted when temperatures drop. With climate change, however, the likelihood of extreme events increases – including colder winter and severe drought as well as record heat – making many of the species living in the bay area extremely vulnerable.

On the coast, the most visual and immediate effect of last winter’s cold was the large number of fishes that floated in from the gulf. The die-off rate was so great that several fisheries, including snook, bonefish and tarpon, were closed to protect the surviving fish. Though similar die offs have occurred in the past – most recently the red tide event of 2005 – the freeze was so prolonged that officials have yet to get an accurate measurement of how severely the fisheries were damaged.

“The lowest temperatures were felt in January and February, but we still had relatively cold weather in March and April, so many fish species took to deeper waters to find more favorable temperatures,” said Luiz Barbieri, program administrator for marine fisheries research at the Florida Fish and Wildlife Research Institute. “Not all of them have returned to those inshore areas where they usually hang out, so we must wait until populations have stabilized to get a reliable assessment.”

Though the cold wreaked havoc on native fisheries, some benefits may come out of it. Many invasive tropical fish suffered from the cold spell, halting their spread, even if temporarily. The visible fish die-off also focused much-needed attention on the importance of preserving habitat for fisheries. Finally, it gives credence to a conservation management approach to key species like snook. “Having a conservation management approach where you keep population levels relatively high, where snook is really strictly managed, gives you a buffer to absorb some of these events that are beyond our control,” said Barbieri.

Cold Kills Hundreds of Manatees

Along with the dead fish, the Florida manatee was also severely impacted by the unprecedented cold weather. Manatees suffer cold stress in water that is 65 degrees Fahrenheit or lower. About 500 manatees have died so far this year – primarily because of exposure to cold weather – in the wake of record low temperatures that persisted into mid–February. The death toll is more than a 100% increase from this time last year.

“Manatees evolved from populations of animals in the tropics,” said U.S. Geological Survey wildlife biologist Robert Bonde. “Charlotte Harbor is really the northern limit of their natural Winter range along the west coast of Florida, so any severe cold weather is going to be harmful unless manatees find adequate warm water.”

However, a silver lining presents itself for overall manatee populations as well. Scientists were better able to count the number of manatees living in Florida waters as they congregated around warm water sources such as springs and outfalls from power plants. More than 5,000 manatees counted in Florida waters during the height of the cold snap in mid-January marked the highest number ever recorded for the endangered species.

The increased population counts made it clear that sustaining a large number of manatees requires preserving more natural artesian springs, keeping aquifers sound and healthy and practicing stringent water conservation, Bonde said.

Seen From the Sky

Maybe the best indication of the historic nature of this freeze event can be seen through fingerprints visible from the sky. Large tracts of brown mangroves dot the landscape from the Everglades to north of Tampa Bay. “There are more freeze-killed mangroves from this event than from the 2004 and 2005 hurricane seasons combined,” said USGS ecologist Tom Smith.

Scientists estimate that over 5,000 acres of mangroves were destroyed from the highly active 2004 and 2005 storm seasons. But the stinging cold temperatures and dry humidity literally sucked water out of mangrove leaves, leaving a rash of dead mangroves around the state. Smith is currently working with aerial surveys to document the full extent of mangrove freezes.

And the freeze may only be the start. The BP oil rig explosion in the Gulf of Mexico is still billowing out millions of gallons of oil that could reach Florida’s coastal environment. “If oil comes to the coast it will be a double whammy for many species in the area,” Smith said. “They are already stressed and hurt as it is.”

Freezing Crops → Depleted Aquifers → Sinkholes

For people living in east Hillsborough County, the rash of sinkholes that developed when farmers began pumping groundwater to protect their crops from cold temperatures became the symbol of the freeze. Like native cold-sensitive species, Florida crops including strawberry and corn won’t survive freezing temperatures. To save Hillsborough County’s largest crop – an industry that adds nearly a billion dollars to the region’s economy – strawberry growers sprayed warm groundwater onto crops to create a protective layer of ice that prevents freezing.

“The water is really used to save the plant more than the berries, because the plant continues to produce fruit throughout the year,” said Ted Campbell, executive director of Florida Strawberry Growers Association. “When it gets cold, the plant is a little less vigorous but to lose it entirely – which would have happened during the unprecedented cold – would have been economically devastating to the area.”

When nearly all of the farmers concentrated in the strawberry producing region of Plant City and Dover began pumping, they lowered the Floridan aquifer to new extreme levels – 25 feet or greater in a matter of a week in certain areas.

“The pumping stressed the Floridan aquifer on the order of tens of feet and that process can relieve the buoyant nature or pressure of the aquifer,” said Jon Arthur, director of the Florida Geological Survey. “Therefore, if you have cavities in the subsurface and they become dry, you increase instability and the probability of the cavity roof collapsing. It ultimately can yield to a failure of that material to form a sinkhole.”

Over 65 sinkholes were reported from Tampa in the west to Frostproof in the east, varying in size with some extending 50 feet wide. They caused damage to property and infrastructure, closing roads and schools, and forcing some residents to abandon their homes.

Currently the Southwest Florida Water Management District is convening a panel of technical experts and stakeholders to address the problem and devise solutions to avoid future problems if similar weather situations occur.

“The entire agriculture community needs to come to terms with how we will handle an event like this in the future, especially with a greater residential population that is increasingly using ground water,” said Campbell. “We are looking into every possible solution, from permitting to creating alternatives to groundwater.”

Matthew Cimitile is a journalist working with the USGS Florida Integrated Science Center office in St. Petersburg.