North Temperate Lakes

Can an ecosystem dominated by an invasive species be forced into an alternate stable state of low invader abundance? Invasive rusty crayfish (Orconectes rusticus) adversely affect native biota when present at high densities; however, at low densities their effects are minimal.  Lakes with high and low densities of rusty crayfish may represent alternate stable states, meaning that crayfish at low densities could be maintained ...

Can an ecosystem dominated by an invasive species be forced into an alternate stable state of low invader abundance?

Invasive rusty crayfish (Orconectes rusticus) adversely affect native biota when present at high densities; however, at low densities their effects are minimal.  Lakes with high and low densities of rusty crayfish may represent alternate stable states, meaning that crayfish at low densities could be maintained for the long term under certain conditions.  I am conducting a whole-lake experiment on Sparkling Lake, Vilas County, Wisconsin to determine whether the impacts of rusty crayfish are reversible, and to attempt to switch Sparkling Lake from a state dominated by rusty crayfish to an alternate state dominated by native species.  Rusty crayfish were trapped from 2001-2008, and fishing regulations were changed in 2001 to increase predation on juvenile crayfish. Crayfish, fish, macrophyte, and macroinvertebrate populations were monitored to determine the impacts of the removal effort.

Results to date:

• Rusty crayfish abundance declined by two orders of magnitude and remains low following the cessation of trapping. 
• No compensatory response has been observed in juvenile crayfish, and female fecundity has declined, indicting the potential for population growth inhibition. 
• Smallmouth and rock bass are preferentially consuming crayfish, as the percentage of crayfish in fish diets has not declined concomitantly with crayfish abundance. 
• Native crayfish densities and macrophyte cover have increased as rusty crayfish densities have declined.
• Bluegill and pumpkinseed sunfish (Lepomis spp.) populations have increased from virtually zero to approximately 2,000 individuals.
• Macroinvertebrate density has declined, which is counterintuitive given previous research.  This discrepancy can be partially explained by changes in the fish community and fish diet composition resulting from the crayfish removal.