By Kelly Novic
Staff Biologist, Save the Manatee Club

Al Gore, when speaking of climate change, stated that “nature is on the run.” In his speech at the Capitol, he stated, “A manatee showed up recently in Tennessee, halfway up the Mississippi River. Another one showed up in Massachusetts, just off Cape Cod. First time ever, he said. It got too hot in southern Florida.”

But, while manatees have indeed traveled to these places, is this because of global warming? How will global warming affect manatees?

The Greenhouse Effect

View an interactive feature on the greenhouse effect, see the impacts of climate change, and take a global warming quiz at National Geographic.com.

Global warming is an increase in the average temperature of the Earth’s near-surface air and oceans. Temperatures can increase when gases from the sun and other sources are trapped within the Earth’s atmosphere. These gases, known as “greenhouse gases,” then prevent heat from leaving the Earth.

Greenhouse gases can come from both natural and man-made sources. Historically, events such as explosions on the sun, volcanic eruptions, or large meteor impacts have caused large-scale warming and ice age events. These events caused widespread changes to the Earth’s climate and oftentimes resulted in multiple species’ extinctions.

Today, man-made sources are primarily to blame for global warming. The Intergovernmental Panel on Climate Change (IPCC) states that, since the mid-20th century, most of the observed increase in globally averaged temperatures is very likely due to the increase in anthropogenic greenhouse gas concentrations and not natural causes alone.

Measure your "carbon footprint" at the EPA web site to see the effect of your lifestyle and how you can reduce your impact.

We add gases to the atmosphere by driving our cars, heating our homes, and burning “fossil fuels” such as gasoline and coal. With all these gases trapping heat in the atmosphere, the Earth’s temperatures are increasing. As a result, polar ice caps and masses are melting, causing the world’s oceans to rise.

The rapid rate of warming we are currently experiencing makes it difficult for the Earth’s systems to adapt. Nature “on the run” refers to the rapid migration necessary for plant and animal life as temperatures and sea levels rise. However, plants and animals may have a hard time migrating or growing fast enough or may be prevented from doing so by human development.

With all of these events occurring, where does the Florida manatee stand (or, well, swim)? Some individuals have speculated that warmer waters will prove beneficial for the manatee. This, in all likelihood, just scrapes the surface of the global warming challenges facing the species.

Unfortunately, seagrass beds, a primary food source for manatees, must be able to grow quickly enough to colonize shallower areas as sea level rises. Needing ample sunlight to live, seagrasses will die if they cannot remain in shallow, relatively clear waters. As sea levels continue to rise, paving or man-made walls may make it impossible for the grasses to grow. A vast amount of money will be spent to protect homes and property as water levels rise, but bulkheading, seawall construction, and other developments will prevent seagrasses and other species growing into new areas. Such developments also have the great potential of eliminating or blocking migration routes for manatees. In addition, certain species of seagrass and other vegetation cannot withstand temperatures above a certain threshold. Entire seagrass communities may be lost as water warms up and as it intrudes inland.

Global warming could have an adverse effect on seagrass -- a primary source of food for manatees. (Photo courtesy of the Florida Fish & Wildlife Conservation Commission.)

There is also concern over storms. Warmer air can contribute to more frequent and intense storms. Florida’s hurricane season of 2004 gave us a taste of this unpleasant trend.

According to a study by Langtimm & Beck (2003), individual manatees can be killed, displaced, or suffer delayed effects to health and reproduction due to community or ecosystem changes brought about by hurricanes. The magnitude of impact will vary with the destructiveness of the storm, the density of manatees in the area, the number of storms within a season, or coincidence with other mortality factors. With power plants set to go offline in the not-too-distant future, manatee density in remaining warm-water sites is certainly an alarming factor to consider. If a hurricane were to travel over a remaining warm-water site while manatees were present, a significant segment of the population could be killed.

Florida red tide bloom of Karenia brevis. (Photo courtesy of Karen Steidinger, Florida Fish & Wildlife Conservation Commission.)

Additionally, storm surges can force seawater into brackish and freshwater habitat, raising salinity and negatively effecting manatee food and drinking water sources. Along with storms is the threat of increasing red-tide events that can be intensified or extended by heated waters.

The ability of the population to recover would be further impeded by its small size, long generation time, and low reproductive rate. Combined with other sublethal stresses that have chronic and debilitating effects (such as injury and mutilation from boat collisions, variable winter refuges, and degraded feeding areas), manatees become even more vulnerable. Unfortunately, reclassification and delisting criteria and benchmarks are based on data and analyses from years of research in a mild hurricane cycle and “may not be adequate to meet challenges posed with the new active cycle and long-term global climate change” (Langtimm & Beck, 2003). Combine global warming with increasing threats of watercraft collision, red tide occurrence and duration, as well as the inevitable power plant closures, and manatees are going to be facing a dire future.

So did those manatees in Tennessee and Cape Cod travel there because it was too hot in Florida? Probably not, but we can’t be sure. Will global warming effect manatees? Yes, but maybe not in ways that are easily predicted. As with almost all large-scale environmental events, it is hard to pinpoint one specific source of the problem and one sure-thing solution. Our Earth is a complicated and delicate balance of many systems.

Residents rescue a manatee stranded by the storm surge after Hurricane Charley hits Florida in 2004 . (Photo © Gary Coronado,Palm Beach Post/ZUMA Press )

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Get More Info!

• Read research on Hurricanes and Florida Manatees by Catherine A. Langtimm and Cathy A. Beck of the U.S. Geological Survey's Sirenia Project.

• Try another personal impact calculator, join the Global Warming Virtual March, and get tips on what you can do to reduce your impact at ClimateCrisis.net.

• Check out the EPA's Climate Change Kids Site.

• Investigate Climate Connections, a yearlong series by NPR and National Geographic exploring how climate is shaping people and how people are shaping climate.

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