Conserving The Everglades: Less Is More

"The choice of conservation areas solely on biodiversity may systematically bias the process against such habitats," says Joel Trexler of Florida International University in Miami, who presents this research with his colleagues in the August issue of Conservation Biology.

The Everglades have low biodiversity due to low levels of nutrients, which enter the ecosystem primarily from rain. Other ecosystems with low nutrient levels and low biodiversity include the arid Mediterranean, Antarctica and the deep sea bottom.

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.

Trexler and his colleagues compared levels of algae, invertebrates (including crayfish, grass shrimp and dragonflies) and fish (including large mouth bass and spotted sunfish) in areas that did and did not receive high-phosphorus runoff. These areas near agricultural runoff had up to 2.5 times more phosphorus in the top 4 inches of their soil.

The researchers found that compared to other freshwater wetlands, the Everglades' low-phosphorus areas had unusually high levels of dense algae mats and unusually low levels of invertebrates and fish. These areas were a patchwork of sawgrass and spikerush. In contrast, the high-phosphorus areas had much lower levels of algae and much higher levels of fish (up to 20 times higher biomass). These areas were dominated by dense stands of cattails.

"We think nutrient additions will ultimately lead to monocultures of cattails that choke light penetration into the water and stifle the productivity of aquatic animals," says Trexler. To preserve the Everglade's unique character, the researchers recommend controlling the quality of the water entering it by reducing agricultural runoff as much as possible and filtering the rest through marshes.