Scientists say Lake Superior has a new resident, and it moves in reddish swarms at night. A tiny invasive crustacean known as the bloody red shrimp has now formed a self-sustaining population in the Duluth-Superior Harbor, researchers say in a study published in the Journal of Great Lakes Research. First spotted in the other four Great Lakes in 2006 after arriving in ballast water from overseas freighters, the shrimp had only turned up sporadically in the harbor—until teams found them there consistently in 2023 and again this spring. That confirms the species survived the winter and is now reproducing, says University of Minnesota Duluth biologist Donn Branstrator.
The shrimp, about a quarter- to half-inch long with red-spotted translucent bodies, hide by day and can swarm near piers and breakwaters after dark. Researchers say the species, native to the Black and Caspian Seas, likely reached Lake Superior from the other Great Lakes via domestic "laker" ships that move iron ore between ports, MPR News reports.
How disruptive they'll be is unclear: they eat plankton and algae and could compete with native species, but their relatively large size also makes them potential prey for fish. "That could potentially end up being a positive outcome of their new presence in the food web," Branstrator says. "So, in the balance, I don't think we really know yet." Researchers are expanding sampling sites around Lake Superior's shores as they track the newcomer's spread. Branstrator calls the find a reminder that, despite prevention efforts, aquatic species "are still on the move."
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