WHERE HAVE ALL THE CRANGONYX GONE - THE DISAPPEARANCE OF THE AMPHIPODCRANGONYX PSEUDOGRACILIS, AND SUBSEQUENT APPEARANCE OF GAMMARUS NR. FASCIATUS, IN THE OHIO RIVER

Sampling conducted by personnel of two separate laboratories of the U. S. Environmental Protection Agency showed a single amphipod species, C rangonyx pseudogracilis, present in the Ohio River before the early 19 70s. Subsequent sampling by personnel of both laboratories, along with invertebrate collections made by the West Virginia Department of Natu ral Resources and the first author of this paper showed that this spec ies disappeared from the river in approximately 1973. Another amphipod species, Gammarus nr. fasciatus, invaded the Ohio River in 1973. Gamm arus nr. fesciatus spread rapidly throughout the Ohio River, and is no w one of its most common macroinvertebrate species. Although the evide nce is circumstantial, it seems likely that the elimination of C. pseu dogracilis from the Ohio River was caused by the damming of the river, especially the use of high-lift dams, completed from 1936 through the present. Experimental evidence indicates that the existing amphipod, G. nr. fasciatus, has a proclivity for slow-water conditions, which ha ve been favored by the installation of the high-lift darns.