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Everglades at a Crossroads:
Shrimp, Alligators Key to Success


Scientists will be keeping a close eye on alligators, shrimp, storks, and approximately 100 other key species and environmental elements in the Everglades. Like canaries in a coal mine, these species have been selected as indicators of a healthy ecosystem. How they survive and flourish will be the yardsticks of whether the U.S. Government’s $8-billion Comprehensive Everglades Restoration Plan to restore the unique South Florida preserve is money well spent.


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A typical Everglades landscape shows marshy areas with some open water.
Photograph courtesy South Florida Water Management District
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For nearly six million years, the Everglades—a vast “River of Grass”—flowed south from Florida’s Lake Okechobee, spreading out over thousands of marshy acres as its water crept toward Florida Bay, approximately 100 miles (160 km) to the south, creating rich habitats for alligators, panthers, and millions of wading birds.

What did it look like before engineers built canals and levees to alter its flow, to divert water to a booming south Florida population and drain the land for agriculture, houses, and shopping centers? And how can scientists begin the difficult task of monitoring the success of the twenty-year Comprehensive Everglades Restoration Plan (CERP), which was approved by President Clinton in December 2000?

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Wood storks have changed their nesting patterns due to manmade changes wrought on the Everglades.
Photograph courtesy South Florida Water Management District
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John Ogden, a biologist with the South Florida Water Management District, has been working with a team of scientists since the early 1990s to create models that show what the Everglades look like now—and also what the Everglades may have looked like before humans began to interfere—when the unique subtropical ecosystem was nearly twice its present size.

Ogden’s models have identified key stressors to the Everglades ecosystem, and pinpointed the plants, animals, and changes in water distribution that will be the most likely indicators of restoration success.

As co-chair of the Everglades Restoration Task Force Science Coordination Team, Ogden has developed an adaptive assessment plan that will track about 100 important indicators of Everglades health—from water depth to crocodile counts—as CERP is implemented beginning in 2001.

Divided into hydrological and biological categories, the indicators cover the broad range of species and habitats in the Everglades ecosystem. Hydrological indicators include water depth, salinity levels, and most importantly, flow. “It’s critical to the ecosystem that the water moves through the Everglades,” says Ogden.

Shrimp, Alligators, Wading Birds

Since the Army Corps of Engineers began “plumbing” the Everglades in 1948, often not enough freshwater has reached the end of the River of Grass in Florida Bay. As a result, seagrass, alligators, and pink shrimp among other species, have suffered from levels of salinity they cannot bear.

More than thirty years of data collected on pink shrimp harvests have shown that they are most productive when the salinity in the bay is low—about 30 parts per thousand, says Joan Browder, a scientist with the National Marine Fisheries Service.

As pink shrimp are the major food for many Florida Bay species, including a number of game fish,“they represent an important link in the food chain, and a key indicator of Everglades health. They’re converters—they take energy from the lowest ranks of the food chain and convert it into energy for species farther along,” says Browder. The shrimp, which are harvested in the Dry Tortugas west of Key West, also contribute a significant amount to Florida’s economy.

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Alligators are among the more than 100 indicators of Everglades health. The Everglades is the only place in the world where they coexist with crocodiles.
Photograph courtesy South Florida Water Management District
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Closer to the top of the food chain, alligators are also important indicators of salinity. Baby alligators are especially sensitive to high levels of salinity—they lack the desalinating glands that crocodiles possess. While no longer considered endangered by most scientists, changes in the flow of water in the ecosystem have affected their food supply, and pollution has also affected some populations.

Wading birds, whose numbers declined as much as 90 percent in the twentieth century, are also vitally important monitors of Everglades health.

Some species, such as the wood stork, have completely altered their historical nesting patterns due to changes in the food supply in the Everglades, says Ogden. “Their nests are often destroyed by heavy rains and floods because the birds now nest at different times of year to keep up with changing concentrations of fish.”

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“Tree islands” are slightly raised portions of land that support groves of hardwood trees and provide important habitats in the Everglades.
Photograph courtesy South Florida Water Management District
ENLARGE >>
Balancing Act

But just putting more water into the system isn’t enough, says Ogden, who stresses that the amount of water and its distribution throughout the system is critical.

“Tree islands”— slightly raised parcels of land that are home to groves of hardwood trees—are a good example of why the way water needs to be restored to the Everglades is important. “We have to make sure we’re putting more water into the system, but not making it so deep that the trees will drown.”

“The natural Everglades almost never flooded,” says Ogden. “The managed Everglades floods far more often, killing lots of trees.”

The restoration effort is a “balancing act,” says John Ogden of the nearly $8-billion plan. As the Everglades restoration continues, each “indicator” will be subject to a yearly audit. “The measure of success will be if the birds return to their old patterns, and we begin to see positive changes in the Everglades.”

CERP will have to be monitored closely, says Ogden. “If we see some parts of the plans aren’t working, we may have to go back to Congress.”


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More Information
The Everglades is a diverse ecosystem of sawgrass prairies, mangrove and cypress swamps, pinelands, and hardwood hammocks, as well as marine and estuarine habitats. Everglades National Park, which was dedicated in 1947, encompasses more than 2,300 square miles (6,000 square km) in southwestern Florida. The region was designated a World Heritage site in 1979, and has also been declared an International Biosphere Reserve, and a Wetland of International Importance.

Since the 1950s, the Everglades has seen the degradation of its unique ecosystem due to a system of canals and levees constructed by the Army Corps of Engineers to control the flow of water in the region. Rather than solve any problems, the system has created unnatural cycles of drought and flooding that have upset the balance of nature, and seriously threatened the survival of many of the Everglades’ most important native species.

The Comprehensive Everglades Restoration Plan, which will cost approximately U.S.$ 8 billion over approximately 20 years, is a massive blueprint aimed at undoing some of the damage to the River of Grass.