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Berg, D.J., 1992. The Spiny Water Flea, Bythotrephes cederstroemi: Another Unwelcome Newcomer to the Great Lakes, Miami University.
Fact Sheet 49 (1992):
2 Pages A fact sheet produced by the Ohio Sea Grant College Program The Spiny Water Flea, Bythotrephes cederstroemi: Another Unwelcome Newcomer to the Great LakesIn the last 100 years, many nonnative (a.k.a. exotic) aquatic organisms have become established in the Great Lakes. These include the sea lamprey, various types of salmon, the alewife, and a variety of smaller, less conspicuous species. Most recently, invasions by the zebra mussel and river ruffe have received extensive coverage by the popular press. In most cases, establishment of exotic organisms has been aided by human activities, such as dumping of ballast water from boats, canal building, transport and release of bait species, or intentional stocking of sport fishes. When an exotic species becomes established, it may have unforeseen and devastating consequences for the invaded ecosystem. Parasitism by sea lampreys played a major role in the decline of lake trout populations in the Great Lakes. Among forage fishes (species that serve as food for sport fishes), competition with alewives was probably responsible for diminished numbers of bloater in Lakes Michigan and Huron. In turn, intense predation by salmon (stocked by government agencies) led to declines in the number of alewives in these lakes. It is apparent that the introduction of nonnative species can significantly alter complex ecosystems such as the Great Lakes. One recent newcomer to the Great Lakes is the spiny water flea Bythotrephes (bith-o-TREH-feez) cederstroemi. This species is a crustacean, distantly related to shrimp, lobster, and crayfish. A native of Europe, Bythotrephes made its North American debut in Lake Huron in 1984 and was present in all of the Great Lakes by 1987. The present distribution also includes inland lakes in Michigan and southern Ontario. It is a small creature (about 1/2 inch long) that is planktonic, meaning it must drift with water currents if it is to move long distances. Its long, barbed tail spine, which gives the animal its common name, makes up over half the length of the body and often catches on fishing lines and downrigger cable. Bythotrephes is active in waters it inhabits from late spring until late autumn. As water temperature warms in the spring, individuals hatch from "resting" eggs that have overwintered on the lake bottom. Life span varies from several days to a few weeks. Throughout much of the spring, summer, and autumn, the population is composed mostly of females. These females produce eggs that remain unfertilized and are carried in the mother's brood pouch until they develop into female offspring that are genetically identical to the mother. This cycle of asexual reproduction (requiring no fertilization) continues as long as the water temperature is neither too hot nor too cold and food is abundant. During times of stress, such as low water temperatures in late autumn, both males and females are produced asexually. The presence of males allows sexual reproduction to occur. Fertilized resting eggs develop a thick coating, which allows them to withstand extreme conditions, such as very low or high water temperatures. These eggs are released by the mother and fall to the lake bottom where they remain until conditions are again favorable. The adult Bythotrephes dies following reproduction. Resting eggs protected by a coating allow the species to persist in the lakes through harsh environmental conditions such as Great Lakes winters. The appearance of the spiny water flea in the Great Lakes has scientists at universities and government laboratories, including The Ohio State University's F.T. Stone Laboratory, studying the impact of this invader on other organisms in the Great Lakes. Research results are now becoming available. Entire Paper |
