Manatees and the Changing Climate

By Dr. Katie Tripp
Director of Science and Conservation, Save the Manatee Club

Manatee Feeding on Seagrass
While some have postulated that increased sea surface temperatures associated with climate change may benefit manatees, this view fails to recognize how the species may be affected by the myriad of other consequences associated with climate change, including sea level rise, changes in seagrass abundance and location, and losses of funding as agencies shift resources away from individual species in an attempt to confront climate change. (Photo courtesy U.S. Geological Survey Sirenia Project.)

Imagine a Florida where the coral reefs have dissolved, droughts are the norm, humans are abandoning multi-million dollar coastal homes and retreating inland, daily high tides flood the streets of coastal cities and neighborhoods, and exotic species outnumber natives. Climate change could make this scenario a reality for the sunshine state, with some impacts being observed within as few as 10 years.

What is Climate Change?
Climate change is fueled by the rapid release of greenhouse gases (GHGs) into the Earth’s atmosphere, including carbon dioxide, nitrous oxides, and methane. These gases trap heat, which contributes to changes in Earth’s temperatures. GHGs can come from both natural and human-generated sources. Throughout Earth’s history, events such as volcanic eruptions and large meteor impacts have caused global climate change (including ice ages).These natural events caused widespread changes to the Earth’s climate and resulted in extinction of many species. 

The Greenhouse Effect
The Greenhouse Effect

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What is different about our current climate crisis is the speed of change being driven by human activities including the burning of fossil fuels such as gasoline and coal.  The concentrations of atmospheric GHGs now exceed the levels measured in the last 650,000 years. The International Panel on Climate Change (IPCC), a group of scientists who review and synthesize climate change data in order to make policy decisions on the best available climate science, has concluded that most of the observed increases in average global temperatures during the last 50 years are attributable to anthropogenic (human-caused) GHG emissions.

Mean air temperatures have increased 0.74°C in the past 100 years and 0.65°C in the past 50 years.  The northern boundary of the subtropic zone in Florida has migrated at least 25 miles north since 1970 and the temperature is expected to warm another 0.4°C in the next 20 years. Other alterations associated with climate change include sea level rise, the rate of which may be greater in Florida than some other areas.  Rising air and sea temperatures cause glaciers at extreme northern and southern latitudes to melt, which causes sea level to rise. Additionally, warmer water has a greater volume, which further contributes to sea level rise.  It is expected that the mean global sea level will rise at least 1 meter by the year 2100.  This 1 meter rise would impact 45 of Florida’s 67 counties, representing 49.1% of the state’s population.  Rises of 3 and 6 meters have also been hypothesized, which would displace 61.6% and 72.3% of the state’s population, respectively. 

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

Global rainfall is expected to increase, as is the number of heavy rainfall events, but the number of days between rain events will also increase, leading to an increase in the number of dry days. Warmer air holds more water vapor, which will increase precipitation, but warmer temperatures also speed rain evaporation, which will allow more droughts even in the face of increased rainfall. These dry days will be associated with an increased prevalence of heat waves and longer, more intense droughts. As Florida contains a variety of habitat types, the impacts of climate change are likely to vary throughout the state. Climate scientists no longer refer to these changes as “global warming” because the symptoms of this global process may be associated with cooler temperatures in certain areas, and also because the implications are far more reaching than just temperature alone.

How Will Climate Change Affect Manatees?
Some individuals have tried to simplify the effects of climate change on manatees by assuming that warmer waters will benefit the species.  However, as the previous paragraphs discussed, climate change is comprised of many more facets than just increasing water temperatures.  We also cannot forget that manatees are part of an inter-connected aquatic ecosystem, and are affected by the health of the plants and animals that share this and the surrounding terrestrial ecosystems. As a species, manatees already face a myriad of threats, including watercraft strikes and red tide, which may compromise the long-term health of individuals and impede recovery of the species. As humans adapt to climate change, other species, including manatees, are likely to be adversely affected. 

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.)

Manatees, as herbivores, rely on seagrass as a primary food source.  Seagrass grows in shallow, relatively clear waters.  As sea level rises and is accompanied by increased turbidity and other impacts to water quality, seagrasses will likely be negatively impacted. Over time, seagrass beds may become reestablished, but major shifts in seagrass distribution and abundance could threaten Florida’s manatees, along with the many species of fish and invertebrates that also inhabit seagrass beds. With sea level rise, coastal habitats will also be threatened by armoring, as coastal towns and cities build seawalls to deflect rising waters. Such human made structures can be detrimental to benthic habitats, including seagrass beds. 

As coastal habitats change, manatees and boats may find themselves traversing new travel corridors that are not protected by manatee speed zones. Additionally, with a changing climate, manatees may extend their range farther north along the Atlantic coast and west along the Gulf coast.  These adjacent states currently lack well-defined manatee speed zones, and residents are not accustomed to sharing the waterways with manatees.  Manatees will face increased risk if they inhabit waters that lack safeguards for their protection. 

Red Tide
Florida red tide bloom of Karenia brevis. (Photo courtesy of Karen Steidinger, FWC.)

The frequency of intense storms such as hurricanes will increase with climate change.  Manatees may be killed, displaced, or suffer delayed effects to health and reproduction due to ecosystem changes resulting from intense storms (Langtimm & Beck 2003).  The magnitude of impact varies 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. Storm surge, in addition to rising sea levels may cause saltwater intrusion in certain freshwater aquifers and other coastal waters that currently provide sources of freshwater vegetation and drinking for manatees.  Manatees will need to adapt to such changes in order to survive.  More intense rainfall and inundation events may result in more frequent red tide events, fueled by nutrient runoff to coastal waters. Such events can be fatal to large numbers of manatees.

Perhaps the most challenging obstacle that manatees will face with a changing climate is a lack of financial resources dedicated to the protection of this species. As human priorities shift to disaster reduction, concern for wildlife may decrease, and agency funding may shift away from individual species.

What Can Be Done?
In order to protect manatees and Florida’s future, we must curb our greenhouse gas emissions, stop building and rebuilding in Florida’s coastal high hazard area, and educate ourselves about the potential impact of climate change, both on our generation and future generations.  Experts have stated that at least an 80% decline in GHG emissions is needed by 2050 in order to avoid the most severe climate impacts. Forests and wetlands must be protected because they act as carbon sinks, removing carbon dioxide from the atmosphere and helping attenuate greenhouse gas emissions. We need to invest in the health of our ecosystems because healthier systems will be more resilient against a changing climate. All citizens should support the development of federal climate change legislation (also known as cap and trade legislation). Every proactive step we take will help safeguard the future for manatees and ourselves.

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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