Spiny water flea (Bythotrephes cederstroemi)
The spiny water flea (SWF) is a species of zooplankton (small, free-swimming crustaceans), native to lakes of northern Europe and Asia. This species was discovered in Lake Huron in 1984. It quickly spread through the Great Lakes, and within a decade, had invaded hundreds of inland lakes in the Great Lakes region. SWF were discovered in Gile Flowage (Iron County) in 2003 by researchers at the UW Center for Limnology. Ddditional populations were discovered in Stormy Lake (Vilas County) in 2007 and the Madison chain of lakes (Mendota, Monona, Waubesa, Kegonsa) in 2009.
The first SWF population in Wisconsin was discovered in 2003 in the Gile Flowage in Iron County. This impoundment was not considered a likely candidate for SWF invasion based on its poor water clarity. On the other hand, this impoundment lies in close proximity to Lake Superior. The location of the Gile Flowage allows it to serve as a stepping stone for SWF to colonize the hundreds of potentially vulnerable lakes of the northern highlands lake district of Wisconsin that offer suitable habitat for SWF (Havel and others 2005). In 2007, the spiny water flea was discovered by the Center for Limnology in Stormy Lake in Vilas County.
The current spread of SWF in Wisconsin is cause for concern. SWF are a voracious predator upon native zooplankton species, and have caused dramatic declines in native zooplankton in Canadian lakes. The native zooplankton play two key roles in lakes: they are food for small fish and they consume phytoplankton (free-floating algae), and thus help control algal blooms. The long spine of SWF inhibits consumption by smaller fishes, highlighting their potential for disrupting food webs.
Their impact on Wisconsin's lakes is not yet well understood. Researchers at the UW Center for Limnology are currently monitoring Stormy Lake and the Madison Lakes to understand their effects on water quality, fish populations, and lake ecosystems as a whole. The Madison Lakes are among the most well-studied lakes in the world, and the recent invasion, though unfortunate, does provide an opportunity to better understand their ecological impacts.
An urgent management challenge is to assess which lakes are vulnerable to spiny water flea invasion. One study found that SWF tend to inhabit large, deep, clear lakes in their native range. Application of those results to Wisconsin indicates that a large number of lakes are capable of supporting this invasive species. Researchers at the UW Center for Limnology are currently developing ways to identify which lakes are vulnerable to SWF (Papes et al. in prep).
Papes, M., P.T.J. Johnson, M.J. Vander Zanden. In prep. Modeling spiny water flea distributions. Canadian Journal of Fisheries and Aquatic Sciences