Chicagoans love their beaches, but even the most ardent advocates of citizenship will admit they aren’t exactly beach-goers’ paradise.
So when a longtime Edgewater resident (and WTTW News staff member) stumbled across a sudden abundance of seashells at Lane Beach in early November, something she had never encountered in 10 years of walks everyday, his keen sense tingled in a “it’s strange” genre. so.
Strange indeed. Our esteemed colleague had just come into contact with one of the most menacing creatures to haunt the Great Lakes ecosystem, and yet he did not even recognize the threat to sight.
From photos, scientists at the Shedd Aquarium have identified harmless-looking shells, roughly the size of a penny, like the remains of quagga mussels, an aquatic invader that has wreaked all kinds of havoc in these areas. .
The recent storm surges likely caused shell deposits to deposit at the bottom of the lake and brought them ashore, according to research biologists Shedd Kentaro Inoue and Austin Happel.
While Lake Michigan functioned more like an ocean, with the strong tides and crashing waves needed to provide a constant supply of trash from the depths, it regularly spewed out cargoes of quagga.
Native to the Dnieper River in Ukraine, the quagga hitchhiked to the Great Lakes via ballast water from transatlantic ships and were first recorded in northern Lake Michigan in 1997, near Mackinaw City. By 2002, they had spread to the southern parts of the lake.
Here is a list of the problems they cause, not so good:
– Tie down and obstruct water intake structures like pipes and screens, resulting in expensive maintenance for water treatment and power plants.
– Adhere to boat hulls and engines, increasing drag, affecting steering and causing engine overheating and malfunction.
– Devastate the food chain by supplanting native mussels and other filter-feeding invertebrates (worms, insect larvae, etc.) for food. The result is less food for the smaller fish, so their population is decreasing, which means less food for the larger fish that eat the smaller fish.
– Associated with outbreaks of avian botulism, killing tens of thousands of birds. Because they are voracious filter feeders, quagga can accumulate incredibly high concentrations of pollutants in their tissues, which move up the food chain when contaminated mussels are eaten by predators.
– The filtration of particles by the quaggas improves the clarity of the water, which seems to be a good thing, except that the light is then able to penetrate deeper, changing the species composition of the aquatic plant communities. The result being that this clearer water probably promotes algae blooms.
Quaggas now make up 90% of invertebrate creatures at the bottom of Lake Michigan, according to reports. Yet despite all their dominance, the quagga still manage to go unnoticed due to a certain level of invisibility.
The mussel is not an Asian carp, jumping out of the water and hitting anglers in their boats. And it’s certainly not a sea lamprey, with its hellish nightmare face.
Even among the invasive mussels, the quagga still acts as the second banana behind the zebra mussel, which got here first and continues to enjoy greater notoriety despite being supplanted by the quagga (imagine that Ask Jeeves is better known than Google).
Quagga mussels have a number of advantages over their zebra cousins: they thrive at greater depths (they were found 540 feet deep in Lake Michigan), are more tolerant of cooler waters, and breed. in even greater numbers. In 2000, zebra mussels represented 98.3% of mussels in Lake Michigan; in 2005, they had been wiped out by quagga mussels, which represented 97.7% of harvested mussels.
The point is, to inexperienced eyes the two molds are difficult to tell apart.
If all a person has to believe is a vague notion that a black and white striped shell pattern equates to a zebra mussel, let us blow the usefulness of that criterion out of the water. “Quagga” is the name of a species of zebra that became extinct in the 1880s – (a South African team is trying to revive the animal in Jurassic Park) – ergo, the quagga mussels are also black and white .
In the case of a clutter of seashells like the mass lodged at Lane Beach, eroded and bleached almost beyond recognition, scientists have suggested a number of ways to distinguish between quagga and zebra.
In general, zebra mussels are more triangular or D-shaped, while quagga mussels are rounder or teardrop-shaped, said Inoue.
“The most distinctive feature that I know of is that if you place them on a flat surface, the zebra mussels will stay there, but the quagga mussels will fall because they are not flat on the bottom,” added Karen Murchie, biologist. by Shedd.
Other identifying traits, courtesy of the US Geological Survey, include such things as the appearance of the ventral midline of mussels – the line where the two sides of the shell meet.
But when in doubt, the quagga is the safest bet, Happel said, for one simple reason: “Most zebras have been outmatched by Lake Michigan quagga. “
Contact Patty Wetli: @pattywetli | (773) 509-5623 | [email protected]