Mini Monsters "Musseling" into Missouri
They aren't wrapped like mummies or built from parts scavenged from graveyards; they don't have curved fangs or ripping claws; they didn't come to earth from a distant galaxy to pop unexpectedly from people's bellies, but we've still got good reason to be scared, for a minuscule but monstrous mussel is invading Missouri.
You may never have heard of zebra mussels, but you soon will. As sure as beesbuzz and birds chirp, these dime-sized invaders are going to affect every one of us.
Zebra mussels (Dreissena polymorpha) are relatively new to North America, much less Missouri. The striped mollusks (the alternating, zebra like stripes suggested their name) traveled to this continent from Europe in the late 1980s, hitching a ride in the ballast tanks of ocean-going ships, according to most reports.
They colonized in the Upper Midwest and were first discovered in Lake St. Clair, near Detroit, in 1988. The zebra mussels continued to spread throughout the Great Lakes and, inevitably, found their way into major waterways, including the Hudson, the Susquehanna, the Illinois and, of course, the Mississippi.
The first mussels (10 of them) were discovered in Missouri at the Melvin Price Locks and Dam, north of St. Louis, in September 1991. In November of the same year, four mussels were found at river mile 47, near Cape Girardeau. The mussels were attached to concrete blocks that were anchoring devices meant to sample for zebra mussels.
The mussels are now common in the Mississippi River. Bob Hrabik, fisheries program coordinator at the Conservation Department's LTRM station in Cape Girardeau, estimates that in February each square meter of underwater hard surface in the lower river - wing dams, rip rap, natural rocks - was covered with about 1,500 zebra mussels.
"We're no longer monitoring densities, because we know they are here and we know they are high," Hrabik said.
The mussels are of several different sizes and, therefore, likely contain several different year classes. "We're now looking at how they transfer themselves through the system. Are they coming from the Illinois River or down the river from Minnesota or are they reproducing here?" This latest study involves counting veliger numbers throughout the river system.
Veliger refers to a larval stage of zebra mussels. Each adult female zebra mussel may release millions of eggs during the warm water months. The eggs mature into tiny free-swimming veligers, which float among the plankton and can be dispersed by currents. About 2-4 weeks