Donn Branstrator, an invasive zooplankton specialist, holds a spiny water flea on his finger. This species has invaded all of the Great Lakes. Photo: Chris Hagen
By Megan Hopps
Researchers believe that anchors and fishing lines can help spread the invasive spiny water flea, and Great Lakes fishermen may need to follow stricter equipment cleaning regulations.
While spiny water fleas are not harmful to humans, they shift the biodiversity of the Great Lakes ecosystem, said Donn Branstrator, an ecology professor at the University of Minnesota Duluth.
The spiny water flea arrived in Lake Ontario in 1982 and spread to all of the Great Lakes by the late 1980s.
“They came from the Black Sea area and were transported via ballast water from ships,” said John Lindgren, coordinator of the Great Lakes Lake Sturgeon Collaboration, part of the Minnesota Department of Natural Resources’ Fisheries Office.
Branstrator, a specialist in invasive zooplankton, explains what makes the spiny water flea so influential on the aquatic food web.
“It’s a carnivore, which means that it’s feeding on other zooplankton,” Branstrator said. “That’s its big effect in food webs. It reduces the abundance in the diversity of native plankton in lakes, which is used by a variety of fishes that are feeding on the plankton.”
“Oftentimes there are no natural predators, parasites or competitors to keep their population in check,” he said.
The population grows so quickly that it has an environmental impact on the ecosystem, and smaller fish avoid feeding on it due to a long barb-like tail spine that runs down its body, Branstrator said.
“That long tail spine is a protective device so that small fish can’t feed on it,” he said. “They attempt it and spit it out. Big fish can feed on it, but small fish can’t, so it provides a measure of protection during spring and early summer.
A diagram of the spiny water flea. Photo: Rachel Kraft.
“The bigger fish that do consume them have a big difficulty in passing that spine, so that spine gets hung up in the stomach like a ball and needles,” Branstrator added. “In some of the fish, the spines were penetrating the stomach wall, and the stomachs looked like a pincushion with a bunch of spines sticking out of it. So that’s likely to have some mal-effects of the life of the fish.”
The regulations of cleaning recreational equipment and boats will undergo some serious changes because of the spiny water flea’s effect on the local fish population.
“We think the way they’re getting around from lake to lake is by ensnarement on fishing lines,” Branstrator said. “The females get ensnared on all sorts of recreational equipment. It might be anchor lines as well, or the mud impacted on an anchor.”
A cold winter won’t effect the fleas — in fact, the colder temperatures help initiate their reproductive cycle.
“In the fall, the females can sense a drop in temperature and a decline in food. They produce males, and then mate with their male offspring,” Branstrator said. “So there’s this period of sexual reproduction in September and October, and the end result of that sexual reproduction is an over-wintering cyst or resting egg.”
Spiny water flea eggs can withstand many other environmental stresses.
“You can put them in chlorination for a few days, and they can survive that,” Branstrator said. “You can expose them to salt water or warm temperatures, and they survive that. They’re really durable. They’re believed to be the life stage that helps facilitate dispersal from one location to the next.
“But the eggs of this species are not very resistant to drying at all,” he said.
Branstator’s research of the spiny water flea has helped the DNR Fisheries Office create standards for how recreational boaters and fisherman should clean their equipment to prevent the spread of invasive species to other Minnesota lakes. Fisherman are advised to be careful not to spread these invaders to other lakes to protect the biodiversity of the aquatic ecosystem.