Who Will Invade Next? 5 Species That May Threaten Wisconsin Waters

When zebra mussels were finally found in Lake Mendota in the fall of 2015, most aquatic ecologists in Wisconsin had the same thought – “What took them so long?” These notorious little bivalves were firmly planted on the radar of resource managers and scientists, since they had already overrun the Great Lakes and had been moving into Wisconsin waters for years. Which begs a couple of questions. What else is out there that keeps lovers of Wisconsin’s waters awake at night? What species might invade next? 
We asked new Center for Limnology director, Jake Vander Zanden, who has made a career out of studying invasions, to give us his Top Five:

1. Quagga Mussels 
Minnesota Aquatic Invasive Species Research Center (Culver)

Quagga mussels and zebra mussels seem to go hand in hand, where one is, the other soon follows. Like zebra mussels, quagga mussels were brought to the U.S. from somewhere around the Ukraine and the Caspain Sea in the ballast water of ocean-going ships headed for Great Lake ports. Since the first documented specimen was found in Lake Erie in 1989 and the Mississippi River near St. Louis in 1995.
By the mid 2000s, they’d made it to Lake Superior and had made unexpected jumps to ecosystems as far flung as Lake Mead in Nevada, Lake Havasu in Arizona, which begs the question, if they’ve made it that far West, what’s keeping them from Wisconsin lakes? .
Scientists worry about quaggas, says Vander Zanden, because “they colonize soft substrates and can tolerate low oxygen. Thus, they would reach much higher densities than our current zebra mussel population in Lake Mendota and other silt-bottomed lakes and would have much stronger effects, as has been the case in the Great Lakes, where they, along with zebra mussels, have clogged water intake pipes, upended the food web and concentrated nutrients and pollutants down at the bottom of the lakes. 
Read more on this USGS FAQ Sheet
 2. Round Goby
Michigan Sea Grant

“The roundy goby will do well in Lake Mendota now that we have zebra mussels, which is their favorite food,” says Vander Zanden. And, indeed, this is a prediction also anchored in what we’ve seen play out in the Great Lakes. Shortly after zebra mussels were discovered in Lake Erie, round gobies – which are also natives of the Caspian Sea and likely transported in ballast water when their larvae got sucked up into the holds of ocean-going tankers – turned up in Lake St. Clair. According to Michigan Sea Grant, “Once established, gobies can displace native fish, eat their eggs and young, take over optimal habitat, spawn multiple times per season and survive in poor quality water.” In other words, they can do all the things that gets an exotic species slapped with the “invasive” label. 
In the Great Lakes, round gobies have been particularly rough on native bottom-dwelling fishes like the mottled sculpin, which has been “virtually eliminated” in many areas where gobies have moved in and chased male sculpin off of prime breeding habitat. Round gobies have also played a role in avian botulism outbreaks in the Great Lakes where thousands of birds have died. The gobies pick the toxin up when they eat infected zebra mussels and then pass it on to the things that eat them, like loons, mergansers, long-tailed ducks, cormorants and gulls. 
Read more from Michigan Sea Grant here

3. Gizzard Shad
John Lyons, Wisconsin DNR

Unlike our first two entries, gizzard shad aren’t entirely foreign to Wisconsin waters. According to the USGS, their native range extends to the southern and western edges of Wisconsin, especially in and around the Mississippi River. But, like most invasive species, this oddly named and oddly shaped fish – got a hand in expanding its range from humans, as waterways constructed in the Great Lakes, like the Ohio Canal and Chicago River Canal, helped them move in to new waters. As did it’s popularity as a bait fish and accidental introductions from inattentive anglers. Gizzard shad have also been stocked as a forage fish for popular sport fishing species where they are good eating for other fish while young but have the slight problem of growing too big as adults for most species to prey on. 
While gizzard shad’s northern expansion has been somewhat limited by our cooler waters, Vander Zanden says, “with a warming climate, this small forage fish will find the Madison lakes suitable before long. It tends to get really abundant and feeds on organic matter off the lake bottom and then excretes nutrients that then get taken up by algae, fueling greater algae growth. It’s a species that could really change the ecosystem – again.”
Underscoring this point, consider this from the USGS’s Non-indigenous Aquatic Species website: “Gizzard shad show tremendous invasion potential. After only two plantings totaling 1,020 fish in Lake Havasu, the species spread through the Colorado River from Davis Dam southward to the Mexican border, the Salton Sea, and associated irrigation ditches within only 18 months (Burns 1966).” This incredible abundance has led the shad to compete with native fishes, especially members of the sunfish family like bass and bluegill, for food and there is some evidence that sunfish numbers drop once shad become the dominant fish species in a system. 
Learn more on the USGS website. 
4. Common Water Flea (Daphnia lumholtzi)
Ruhr-University Bochum, Germany via Flikr and the CC BY-NC 2.0 license. 

Readers of this blog will no doubt have positive associations with the word Daphnia, since we write so much about our awesome native grazers of algae, Daphnia pulicaria. But Daphnia lumholtzi, or the invasive common water flea, is a whole different story. 
Originally from warm water bodies in Africa, Asia and Australia, the common water flea somehow got a lift to U.S. waters and has been taking advantage of increasingly warm mid-summer waters ever since. Like the spiny water flea, another invasive zooplankton in the Madison lakes, Daphnia lumholtzi grow spines that make them difficult for some fish to eat. Once they become too abundant, says Tim Campbell, an aquatic invasive species specialist at Wisconsin Sea Grant and the Wisconsin Department of Natural Resources there’s less for plankton-feeding fish to consume and they may struggle to find alternative food. “This can lead to movement of fish out of the area or reduced growth rates in fish that remain in waters invaded by the common water flea,” he says. 
In 2008, says Campbell, a detection of Daphnia lumholtzi in Pool 8 of the Upper Mississippi River near La Crosse suggested that the species was more widespread than originally believed in Wisconsin. Scientists believe that a major mode of transportation for this invasive species is in the bilge water or bait buckets of boats moving between different waterbodies, so the importance of “clean, drain, dry” for boaters is immense. While studies have shown that competition between Daphnia lumholtzi and native Daphnia species may not be too disruptive, it’d probably be best to keep the two separated. 
5. Bloody Red Shrimp (Hemimysis anomala)

Wisconsin Sea Grant

With a name ready-made for a horror movie, bloody red shrimp sounds like a species to strike fear in the heart of any native species. But, so far, the tale of this recent Great Lakes invader is more of a mystery. It is native to – you’ll never guess – the Caspian Sea and spread across European waterways before being sucked up in the ballast water of an ocean-going vessel and being dumped in the Great Lakes Basin. It was first detected in water samples from Lake Michigan that were collected by NOAA near Muskegon, Michigan. Since then, it’s also been detected in Lake Ontario, making scientists suggest that it’s more widespread than is currently documented. 

According to Wisconsin Sea Grant, a swarm of bloody red shrimp “has a unique swarming behavior unlikely to be confused with anything else in the Great Lakes.” During daylight hours, the animal avoids direct sunlight “and may be observed forming reddish swarms in the shadows of piers, boats or breakwalls.” Like most invasive species, it seems to have a gift for growth – it lives for 9 months, can grow to maturity in 45 days and produce four generations of offspring a year, which is a far more rapid and prolific lifestyle than native shrimp in the Great Lakes. 

As far as getting from our giant Great Lakes to inland Wisconsin waters, Vander Zanden says not to rule this mysterious invader out. “It lives in rocky shallow areas and has been spreading to new lakes lately,” he says. “Who knows what it would do to the food web?”
Wouldn’t it be great if we never found out?