Low biodiversity key to Everglades survival

Low biodiversity is a unique part of Everglades ecology.

August 10, 1999
Web posted at: 3:50 p.m. EDT (1950 GMT)

Biodiversity may be the buzzword of the day, but there's far more to conservation than sheer numbers of species, say Florida researchers.

A report published in the August issue of Conservation Biology suggests that less truly is more in the wetland prairies of the Florida Everglades. Here, the report argues, low biodiversity is intrinsic to the ecosystem's uniqueness and so should be preserved.

"The choice of conservation areas solely on biodiversity may systematically bias the process against such habitats," said author of the report Joel Trexler, a scientist at Florida International University in Miami.

Generally habitats with low nutrients have low biodiversity, Trexler says. The Everglades have low biodiversity due to low levels of nutrients, which enter the ecosystem primarily from rain.

"The Everglades is an ecosystem with fairly low biodiversity in some groups like freshwater fishes, amphibians, and reptiles. There are several reasons for this: the region's recent geologic history, its isolation at the tip of a long peninsula, its low diversity of aquatic habitats, and because of low nutrient levels. "

The fact that the Everglades have low nutrient levels makes them particularly susceptible to nutrient pollution, says Trexler. The main source of nutrient pollution there is high-phosphorus runoff from the Everglades Agricultural Area, the northern third of the historic 3,000-square mile marsh that was drained for agriculture in the early 1900s.

Periphyton grows densely in the Everglades.

The report identifies the naturally low levels of nutrients and the patterns of aquatic plants and animals that thrive under such conditions, as a characteristic quality of the Everglades.

"We demonstrated that those patterns are lost when nutrient pollution enters the Everglades. We suggest that these types of ecosystem patterns may be overlooked by criteria commonly used to identify locations worthy of conservation," Trexler said.

A specific example of the importance of low nutrients in the Everglades is found in the presence of the dense floating mats of algae called periphyton.

Trexler notes that the Everglades has among the highest biomass per unit area of algae (important primary producers) of any ecosystem that has been studied. However, these mats are composed of species that thrive in low-nutrient conditions. The extensive algal mats are a characteristic of the Everglades that contribute to making it a unique ecosystem.

"In an unusual twist of textbook ecological patterns, the Everglades has high biomass of primary producers (the periphyton), but unusually low biomass of aquatic invertebrates and fishes that might consume those primary producers. When nutrient pollution enters the ecosystem, the algal mats disappear, but the biomass of aquatic animals actually increases," Trexler said.

He points out that aspects of the Everglades that the public would identify as important to conserve, such as rookeries of the wading birds that feed on small fishes and invertebrates, ultimately depend on ecological processes like the delicate balance between periphyton and small aquatic animals that live there.

"Decisions about ecosystem conservation must involve consideration of a wider range of characteristics than previously incorporated to avoid overlooking or changing the unique characteristics of such systems," Trexler said.

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