Highly Invasive Exotic Spiny Water Flea Pose a ‘Clear and Present’ Threat to the Aquatic Food Webs that Sustain our Freshwater Ecosystems

By January 15, 2023 News

by Scott Brown

MWA e-Newsletter Editor

First observed in the waters of Lake Huron in the late fall of 1984, aquatic biologists suspect that exotic invasive spiny water flea (scientific name: Bythotrephes longimanus) entered the Laurentian Great Lakes region via the ballast water discharge of a commercial freighter that had entered the freshwater inundated North American continent after navigating from Europe. A native of the Ponto-Caspian Sea region of Eastern Europe and western Asia, the predatory zooplankton species commonly referred to as spiny water flea likely spread via currents, inter-lake ballast water transfers, and recreational boaters to Lake Ontario by September of 1985, to Lake Erie by October of 1985, to Lake Michigan by September of 1986, and to Lake Superior by August of 1987.

Characterized by a distinctive black eye spot, a single long spiny tail, and an opaque body that ranges from one quarter (.635 cm) to five eights (1.59 cm) of an inch in overall length, spiny water flea are capable of explosive rates of population growth due their inordinate capacity to reproduce asexually by cloning themselves in relatively warm waters that are present in late spring and summer, and by reproducing sexually in the cold waters of late fall by producing and fertilizing eggs that are capable of remaining viable for long periods of time due to their inherent resistance to freezing and drying.

The presence of exotic aquatic invasive spiny water flea represents a ‘clear and present’ danger to the freshwater ecosystems that they invade due to the fact that they make their living by aggressively preying upon often abundant and highly beneficial native zooplankton species such as Daphnia that serve as the primary food source for juvenile fish, and that help achieve and sustain clear water in most of our lakes by grazing upon unicellular green algae phytoplankton species that are generically referred to as diatoms. Aquatic biologists fear that declines in the abundance of Daphnia and other native zooplankton species that are heavily preyed upon by spiny water fleas will significantly alter the food web of the Great Lakes, and therefore reduce the number of young phytoplankton eating fish that are capable of surviving their highly vulnerable first year of life. Researchers have also observed that some valuable Great Lakes species such as chinook salmon, walleye, white bass, alewife, yellow perch, white perch, and lake whitefish often consume spiny water flea. It is not currently known, however, how nutritional the exotic spiny water flea is for fish, given the significant portion of the species overall biomass that is comprised of exoskeleton, and the namesake long spiny tail that are known to possess little or no value nutritional value.

The substantial threat posed to invaded freshwater ecosystems is amplified by the fact that spiny water flea deploy a highly effective survival strategy that allows them to avoid being preyed upon by migrating into deeper, cooler, light deprived waters during the day, and by returning to the upper layers of the water column to feed at night under the cover of darkness. The capacity of spiny water flea to disrupt the aquatic food webs that help sustain a myriad of fish species is also enhanced by the fact that many of the fish that inhabit our inland lakes such as bluegill and red eared sunfish are incapable of eating the highly invasive exotic zooplankton species due to their long spiny tails.

The telltale existence of the highly invasive exotic zooplankton species within a particular lake is usually initially detected by sport fisherman whose fishing rod eyelets become clogged with spiny water fleas, or downrigger cables that become inundated with the black eyed, spiny species.

In addition to becoming aware of the fact that this highly invasive exotic zooplankton species continues to spread from lake to lake in the Great Lakes region, recreational boaters and sport fisherman can help prevent the species from entering your favorite lake by remembering to ‘Clean – Drain – Dry’ before transporting their boat and trailer to a new lake.

To learn more about the Michigan State University Extension Clean Boats, Clean Waters program click here