A solitary bloody red shrimp was found in the Twin Ports Harbor, raising fears that the light-hating, zooplankton-eating invasive critters have found their way to Lake Superior.
If it does represent the beginning of an invasion, it would be the first in many years for Lake Superior. But the tiny shrimp may have been dead on arrival after being dumped from a cargo ship — environmental officials can't be sure.
It was collected last July on Allouez Bay on the east side of the port in Superior as part of routine surveying for invasive species, and identified by the U.S. Fish and Wildlife Service some months later.
"We have no way of knowing how it got here," said Doug Jensen, invasive species specialist with the Sea Grant program at the University of Minnesota, Duluth.
A native of the Caspian Sea in Europe, it was first found in the Great Lakes in 2006 near Muskegon in Lake Michigan, and since then in Lake Erie. Lake Huron and Lake Ontario.
Bloody red shrimp invades Great Lakes
The latest discovery of the invasive bloody red shrimp was in Twin Ports Harbor, where a single specimen was found.
Color of dots represent the year of discovery, yellow (2006) to red (2018)
It's established and reproducing in those areas.
But aquatic biologists aren't certain if or when it will influence Great Lakes ecosystems, Jensen said.
The shrimp grow up to half an inch long, and swarm in concentrations up to 300 hundred per cubic yard, he said. They don't like light, hanging out in the shadows of docks and boats, and coming out to feed on zooplankton at night.
That means they could compete with other zooplankton-eating fish. On the other hand, in the fish-eat-fish world below the surface, the bloody shrimp could represent a new kind of food for species of fish that eat native freshwater shrimp.
"That's more or less unknown," Jensen said.
It's also not at all certain that it would become established in Lake Superior. More than one would have to arrive, survive, successfully compete for food and find mates to breed. That's a tall order, Jensen said.
It's also not clear whether the discovery represents the success or failure of what has been viewed as highly effective ballast water management rules designed to prevent foreign fresh water species from getting to the Great Lakes by hitching a ride on cargo ships. Dubbed the "swish and spit," ocean-going cargo ships from far freshwater ports have been required since 2006 to flush out their ballast tanks with saltwater before entering the Great Lakes.
If the shrimp was alive, that's bad news, Jensen said. If it was dead, it's evidence that the U.S. Coast Guard requirement, which has achieved 99 percent compliance, is working, he said.
"Knowing whether it was alive or dead would supply meaning to the finding," he said.
No invasive species has been identified in the Great Lakes since the rule was established. In fact, the last one to be discovered was the bloody red shrimp in Lake Michigan.
Other foreign species have been found, but have not reproduced enough to become established.
Before that, some 185 new species were introduced into the Great Lakes, including gobies, quagga mussels, spiny water flea and others. Many of them came in ballast water dumped into deep harbors around the lakes.
The Wildlife Service is expected to survey for the shrimp again this summer to see if others are out there. Anyone who sees one or more, especially a swarm, is asked to contact the Wildlife Service or the Department of Natural Resources in Minnesota or Wisconsin.
And since the shrimp could easily be transferred in a bait bucket or live well, Jensen said, boaters should follow the rules for preventing the spread of all aquatic invasives: Clean, drain and dry.
Josephine Marcotty • 612-673-7394
