Invasive 'bloody red shrimp' now established in Lake Superior

An invasive crustacean species native to the Black Sea and Caspian Sea has established a self-sustaining population in Lake Superior, according to a new study published in the Journal of Great Lakes Research.

Hemimysis anomala, commonly known as "bloody red shrimp," was first detected in North America in 2006 in Lake Ontario and Lake Michigan, likely introduced through ballast water from transoceanic cargo ships. Within two years, the species had spread to all Great Lakes except Lake Superior.

Researchers collecting samples in Duluth-Superior Harbor last year found 81 individuals in light traps and nets, confirming the population is now self-sustaining. While individual cases were recorded in 2017 and 2018, the consistent presence last year marks a new threshold.

The shrimp prefer warm, shallow environments and avoid direct sunlight by clustering on rocky lake bottoms or near structures like piers, boats, and docks. At night, they move toward the surface in swarms that resemble reddish clouds.

Scientists say their full ecosystem effects remain unknown, but the species can grow and multiply rapidly—some swarms contain more than 500 shrimp per cubic metre. They consume large quantities of zooplankton, potentially reducing food available for young native fish.

Females typically reach 1.7 centimetres long with translucent bodies and bright red to reddish-orange colouring. To prevent spread, the provincial government recommends inspecting boats, trailers, and equipment after each use and removing all plants, animals, and mud before moving to new water bodies.