ENGAGEMENT
Mass Extinction's Come To America. After an article by John Fleischman , Discover 6/1997
When you think of mass extinctions, you probably think of far away places like the Amazon rain forest, Madagascar, or the tropics of Indonesia. But one of the hottest spots in the modern global biodiversity crisis is the Mississippi River drainage system. When the frontiersmen of the early 1800's first explored the are of the Louisiana Purchase, the found an ecosystem where freshwaters mussels of a group called the Uniods flourished. The Pioneers found species which they gave names like "heelsplitter", "Wabash pigtoe", and "Dwarf Wedge Shell". These mussels were extremely common, but only in a limited range. Each of these organisms would only be found in a very small geographic area, but would utterly infest that region of a river or stream. This high level of endemism led the Mississippi River Basin to generate some 300 different species of freshwater mussels, nearly half of the total number of species in the world. To make a long story short, damming of rivers, alteration of stream channels, run off, and other human factors seem to have exterminated 35 species of fresh water mussels according to the American Malacological Union. Another 126 are or have meet the Union's criteria to be considered or threatened. All of these changes have occurred in only 300 years. That works out to 54 percent of known species.
But the news is not all grim. Michael Hoggarth is a scientist who, while looking for a rare fish in the Walhonding River in Ohio, stumbled across a recently dead shell of the endangered Purple Catspaw. After two years of searching, he discovered the live mussel in the Killbuck Creek, which feeds into the Walhonding River. His searches have raised the known population of these unique Uniods by seven percent, and he's still looking. The chances for the survival of the Purple Catspaw are still very much in doubt, but if the newly discovered populations can be protected, studied, and propagated, the chances continue to improve.
Study of these species is vital. Bivalves are known to have complex life cycles that include numerous stages. At one stage, called a glochidia, the larva attaches to the fin or gills of a particular fish. There it is coated by the fish itself, where it matures for weeks. With luck, the juvenile mussels will land on an acceptable substrate, and continue to mature and grow. With most bivalves, the species of fish needed for this to occur is unknown. Therefore, the mussels could be surviving quite well, but if the fish it parasitizes disappears from only a small part of it's habitat for as little as thirty years, the mussel could quickly die off.
1) What measures do you think would be most helpful to preserve and expand the known populations of the Purple Catspaw?
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2) What ecological legislation could the states in the Mississippi River Drainage pass to improve the habitat for the remaining Uniods?
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