It's difficult to describe the wetlands of the Gulf Coast to those who have not had the good fortune to see them firsthand. The countless waterfowl, shorebirds, wading birds, and other wetland wildlife make dawn in a duck blind in coastal Louisiana a spectacular testimony to the rich abundance and diversity of migratory birds wintering in the marsh. It's one of the finest waterfowling experiences to be found in North America.
The Gulf Coast is also one of the most diverse ecosystems on the planet. Marsh plant communities change with the degree of saltwater influence from the Gulf. Varying levels of salinity create a mosaic of different wetland types, ranging from marine to freshwater. While waterfowl use these different marsh types disproportionately, the birds ultimately use all of the marsh. And no marsh type is completely independent of the others.
|Uncertainty abounds, but the U.S. Fish and Wildlife Service, with input from Ducks Unlimited and others, is working to assess potential oil-spill impacts on scaup, redheads, and other waterfowl.
Salt marsh forms the outer fringes of the coast, where land dissolves into the open waters of the Gulf. While these high-salinity wetlands are of relatively low value to waterfowl, clapper rails and seaside sparrows find them much to their liking. Inland of the salt marsh is brackish marsh, where salinity is about seven to 18 parts per thousand—an amount easily detected by the old "taste test." Brackish marshes, with their moderate salinity, also tend to be somewhat less important to waterfowl. Along the Gulf, however, "less important" does not mean "unimportant." Shallow-water areas in brackish marshes often support large, dense beds of wigeon grass, a favorite food of gadwalls, wigeon, pintails, and green-winged teal. In years when bumper crops of wigeon grass are present, these dabbler species heavily use brackish marsh habitats.
But the waterfowl habitat value of brackish marsh pales in comparison to that of intermediate marsh, where salinities range from about one to seven parts per thousand, and to freshwater marsh, where salinity only occurs in background levels of about 0.5 parts per thousand—about the same as you may find in a glass of tap water. These Gulf Coast marshes support larger numbers and a greater diversity of wintering waterfowl than anywhere else in North America. They host the majority of this continent's gadwalls and resident mottled ducks as well as significant numbers of blue-winged teal, green-winged teal, shovelers, pintails, wigeon, ring-necked ducks, and canvasbacks. Most of these ducks rely on the dense beds of submersed aquatic vegetation that grow in freshwater and intermediate-salinity ponds interspersed throughout the marsh. Several species of pondweed, southern naiad, delta duck potato, and annual plants like wild millet—as well as an abundant supply of small invertebrates—provide the food energy that ducks need to survive winter and fatten up for spring migration.
So far, the oil spill has mainly affected barrier islands, beaches, and salt marsh perimeter vegetation not directly important to waterfowl, but vital to colonial beach-nesting birds such as roseate spoonbills and brown pelicans, and to several species of terns, herons, and egrets. These salt marshes have served as a natural barrier that so far has protected interior intermediate and freshwater marshes from oil. If this trend holds, large-scale impacts to most waterfowl and their habitats may be averted.
Remarkably, at press time various government sources were reporting that nearly 75 percent of the spilled oil was gone—either skimmed, burned, evaporated, or widely dispersed into the Gulf. Hence, while risk of storm damage is always present on the Gulf Coast, it appears that the likelihood of wetland losses from oil damage is diminishing. Good news for a system that has already lost nearly 40 percent of its historic wetlands.