American import threatens Spanish wetlands

Forest and Bird, Issue 281, 1 August 1996, Page 10

American import threatens Spanish wetlands

Source: BBC Wildlife

IN THE Guadalquivir delta, in southern Spain, an internationally important area of wetlands is under foreign invasion. In 1974, the voracious and highly fertile Louisiana red crayfish was introduced to the region, and has spread rapidly across most of the 77,000hectare Dofiana National Park and beyond. As a consequence, the diversity of the aquatic life of the wetlands has diminished. According to Dr Andy Green of the Dofana Biological Station in Seville, "the freshwater marshes have shifted from being a complex ecosystem full of diverse plants and invertebrates to one dominated by crayfish and phytoplankton, with no submerged higher plants." The voracious crayfish have decimated the underwater vegetation. "Almost all the energy flowing through the ecosystem now goes through the crayfish," says Green. This

means that birds that do not feed on the crayfish have to compete for declining food resources. Several snails in the area have been wiped out, partly through crayfish predation, and also because they compete with the crayfish for food. Another hazard to local wildlife is trapping. Fishers are using adapted eel nets in the shallow water of the delta to trap the crayfish and, while this has had little or no effect on the crayfish population, it poses a serious threat to ducks and rails including the globally threatened marbled teal. Formerly the marbled teal’s main breeding ground, the national park once held thousands of breeding pairs. Last year, for the first time, they failed to breed. However, hopes for the teal have been raised by recent rains, which have filled the crayfish-free brackish marshes, and provided safer breeding areas. The crayfish, though, remains firmly entrenched, and is now widespread in Spain and Portugal.