Academic journal article The American Midland Naturalist

Where Have All the Crangonyx Gone? the Disappearance of the Amphipod Crangonyx Pseudogracilis, and Subsequent Appearance of Gammarus Nr. Fasciatus, in the Ohio River

Academic journal article The American Midland Naturalist

Where Have All the Crangonyx Gone? the Disappearance of the Amphipod Crangonyx Pseudogracilis, and Subsequent Appearance of Gammarus Nr. Fasciatus, in the Ohio River

Article excerpt

ABSTRACT.-Sampling conducted by personnel of two separate laboratories of the U.S. Environmental Protection Agency showed a single amphipod species, Crangonyx pseudogracilis, present in the Ohio River before the early 1970s. Subsequent sampling by personnel of both laboratories, along with invertebrate collections made by the West Virginia Department of Natural Resources and the first author of this paper showed that this species disappeared from the river in approximately 1973. Another amphipod species, Gammarus nr. fasciatus, invaded the Ohio River in 1973. Gammarus nr. fasciatus spread rapidly throughout the Ohio River, and is now one of its most common macroinvertebrate species. Although the evidence is circumstantial, it seems likely that the elimination of C. pseudogracilis 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 have been favored by the installation of the high-lift dams.

INTRODUCTION

Recently, Carlton (1996) pointed out that ecologists and biogeographers routinely categorize species as native with a confidence belying the quality of the supporting data. Although the spread of a few exotic species, such as the zebra mussel, Dreissena polymorpha (Pallas), through the Great Lakes and the large rivers of the Mississippi River drainage (including the Ohio River) has been well documented (O'Neill, 1996); Carlton (1996) expressed the view that the number of exotic invasions has been seriously underestimated. Consequently the "sources, recipients, and impacts of invasions may be subject to substantial errors" (Carlton, 1996). An excellent example of this lack of awareness of the status (native vs. exotic) of an invertebrate species is provided by research from the Ohio River. A presentation at the 1996 meeting of the Mississippi River Research Consortium described the effect of zebra mussels on one of the Ohio River's most common invertebrate inhabitants, the amphipod Gammarus nr. fasciatus. The intent of that study was to determine the effects of the exotic zebra mussels on the river's presumably native amphipod population. In reality, G. nr. fasciatus preceded the zebra mussel in the Ohio River by only eighteen years, and the authors, unknowningly, were really studying the effects of one exotic on another.

In this article we document the invasion of the Ohio River by G. nr. fasciatus. We also show that before this invasion, another, and probably native amphipod species, Crangonyx pseudogracis Bousfield, inhabited the river, only to be eliminated from the river about the same time that G. fasciatus invaded.

STUDY AREA

The Ohio River is a very large river located in the east-central United States, formed by the confluence of the Allegheny River and the Monongahela River in Pittsburgh, Pennsylvania. The Ohio River flows 1578 km (981 miles) in a southwesterly direction, joining the Mississippi River at Cairo, Illinois. At its confluence with the Mississippi River, the average discharge carried by the Ohio is twice that of the Mississippi. With the exception of the Mississippi River, the Ohio River carries more freight than any waterway in the United States (Ohio River Basin Commission, 1978).

In order to ensure enough depth for year-round navigation (principally for barges and towboats) during periods of low flow, the Ohio River was modified by the construction of 50 low-lift dams along its length, completed in 1929. Since 1929 most of these low-lift dams have been replaced by sixteen high-lift dams, in order to create longer "pools" between the dams. Twelve of the high-lift dams were completed between 1959 and 1975. The twelve new dams have lifts (differences in elevations between the pool impounded by the dam and the next downstream pool) of 4.9 to 10. …

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