Exotics: a cascade of effects
Can exotic species pave the way for other exotics?

One theory referred to as "invasional meltdown" supports the idea that invading organisms may facilitate one another's establishment and survival, making an ecosystem increasingly susceptible to invasion.

In an essay in the recent State of the Great Lakes 2001 report, Canadian researcher Dr. Anthony Ricciardi supports the meltdown theory, initially developed by researchers from the University of Tennessee. One example is that of zebra mussels in Lake St. Clair, which have dramatically altered water clarity via filtering. According to Ricciardi, the improved clarity "initiated a cascade of effects," ultimately causing exotic weeds to flourish and the fish community to shift from dominance by walleye (a favored sportfish in Michigan) to bass and pike.

Zebra mussels have had other effects as well. Ricciardi explains that zebra mussels "provide food (in the form of mussel feces) and shelter (within clumped shells) to the invading amphipod crustacean Echinogammarus ischnus…" Discovered in the Detroit River several years after zebra mussels, this exotic has now become common throughout the lower Great Lakes.

These types of changes, says Ricciardi, indicate the importance of preventing future exotics from entering the Great Lakes.