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Tiny predator threatens Great Lakes' food web.

A half-inch-sized predatory creature from Europe threatens to disrupt the food web in all of the Grrat Lakes, a National Oceanic and Atmospheric Administration (NOAA) scientist has confirmed. Henry A. Vanderploeg of NOAA:s Great Lakes Envirornmental Research Laboratory in Ann Arbor, Mich., has demonstrated the voraciousness with which Bythotrephes-a European zooplankter-is consuming another type of zooplankter commonly known as the water flea. The latter are a dietary mainstay for juvenile alewives, bloaters, and perch, which in turn are the forage of large predatory fishes such as salmon and trout.

Whether the predators will affect fishing in the Great Lakes, now largely restricted to recreation, depends upon the water depth at which the various species of fish normally feed, as well as food web relations not yet understood, Vanderploeg noted. Bythotrephes tend to concentrate in the upper 65 feet of the water column. Bythotrephes first were reported in Lake Huron in 1984, were found in Lakes Erie and Ontario in 1986, and now have invaded all of the Lakes, Vanderploeg said. It is speculated the predators were transported from Europe in water ballast aboard empty grain freighters from the Soviet Union, and dumped into one or more of the Lakes upon arrival in the United States.

Until now, no reliable data has been available on the extent with which the predators could affect the food web. Vanderploeg used sets of paired traps to capture Great Lakes water with similar concentrations of water fleas and other zooplankters from several sites in Lake Huron. He then introduced a number of Bythotrephes into one of the traps in each pair. After 24 hours during which the predators fed on the zooplankton in the trap, the NOAA scientist compared the concentrations. "The technique revealed very high feeding rates for Bythotrephes feeding on natural prey assemblages," he said. "These experiments confirm the concern that Bythotrephes could have a significant effect on the water fleas, the preferred prey of many forage fishes. It appears that all small zooplankton are vulnerable."
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Title Annotation:bythotrephes
Publication:Marine Fisheries Review
Date:Jun 22, 1989
Previous Article:Cordell Bank named a marine sanctuary.
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