Exotic snail could prove deadly for migrating waterfowl

American Coot threatened by invasive snail.
Bruce E. Lyon
The American coot is one of the top two waterfowl species affected by snail-mediated infections.

The introduced of non-native species are one of the biggest threats to aquatic ecosystems, and their impacts are only made worse when pathogens come along for the ride. One example of this is the Eurasian faucet snail, a species that has been implicated in massive die-offs of waterfowl across the northeast.

The Faucet Snail

First of all, the exotic mollusk isn’t exactly new to the region. The faucet snail, also known as Bithynia tentaculata, was introduced to northeastern North America in the late 1800’s and has been established in the region since at least 1930. It is just one of the many species that have been introduced to the Great Lakes over the years, and it surely won’t be the last.

Faucet Snail invasive species
Sometimes great things come in small packages. Sometimes, they’re not so great. Full grown, faucet snails are only about 1.5 cm long.

Like other unwelcome intruders, the snail is highly prolific, able to reproduce multiple times a year, and remarkably resilient. In addition to fresh water, it can tolerate brackish water, and it can even seal itself inside its shell when it needs protection from chemical pollution or desiccation. The snail is also able to obtain food from by grazing on submerged surfaces, as well as by filtering the water column , ensuring that it will never run out of food. The only saving grace has been that the species lacks a planktonic larval stage. This means that the snail can’t be spread by ballast water like many other introduced species. Instead, it can only make its way into new areas by crawling along the Lake’s shore or by hitching a ride on solid objects like aquatic plants or boat hulls. As a result, the faucet snail has only been able to spread at a snail’s pace.

Exotic faucet snail is now present in all the Great Lakes and causing massive waterfowl die-offs. Click To Tweet

Impact of the Faucet Snail on Native Species

Faucet snails have long been known to occur in the four lower Lakes, but as far as biologists were aware, it had been absent from Lake Superior until around 2010. However, in a  recent publication, a group of researchers led by Anett Trebitz of the U.S. Environmental Protection Agency confirmed the recent establishment of faucet snails in the St. Louis River Estuary and scattered occurrences along Lake Superior’s southern shore.

faucet snail invasive species map
The faucet snail was introduced to the Great Lakes in the 1870’s and has finally established itself in Lake Superior. Map based on data from the Great Lakes Coastal Wetland Monitoring Project funded by USEPA GLNPO to Central Michigan University and created by the Natural Resources Research Institute, University of Minnesota Duluth.

The snail’s expansion into the St. Louis River Estuary is especially concerning given the importance of the area for juvenile fish development and as a stopover for migrating birds. The estuary has been the target for a variety of restoration efforts, including cleanup of industrial waste, restoration of wild rice, and reintroduction of the lake sturgeon, and is considered one of the most valuable ecosystems in the Great Lakes. However, because of its proximity to a major harbor, the river has already had long history of pollution problems and exotic introductions, and the establishment of non-native species like the faucet snail could further compromise the resilience of the ecosystem to ongoing and future disturbances.

Once established, the faucet snail competes with native snail species and has been associated with overall declines in the diversity of mollusks. It’s thought that the snail functions as a food source for introduced carp, and frequently, the snail is found along-side other introduced species. Biologists also fear that the true severity of the snail’s effects are masked by other more harmful invaders, like the zebra mussel, so there may be more bad news on the horizon. The most alarming factor for now, though, is the snail’s involvement in the transmission of deadly parasites to native wildlife.

Exotic snail could prove deadly for migrating waterfowl. #nature #conservation #wildlife Click To Tweet

Snail Parasites and Waterfowl Die-Offs

As it turns out, the faucet snail harbors several parasitic flatworms that were previously absent from the Lakes and that were probably introduced along with the snails. The problem is that the parasites use several hosts to complete their life-cycle, and one of their developmental stages infects waterfowl, which acquire the parasites when they eat the snails. Although the parasitic worms don’t usually cause harm when they infect birds in Europe, where the organisms are from, North American species aren’t adapted to the parasites and the infections can be devastating.

So far, at least 15 species of birds have been affected, and the U.S. Fish & Wildlife Service estimates that the death toll is well over 60,000 birds, with thousands more dying every year. In the spring of 2006 alone, over 20,000 birds were killed at the nearby Upper Mississippi River USFWS refuge. Studies have shown that birds can acquire lethal doses of the parasite from ingesting only a few snails, and then are likely to die within a week. The species most affected are the American coot (Fulica americana) and the already declining lesser scaup, Aythya affinis.

lesser scaup snail die-off
The lesser scaup is one of the top two waterfowl species affected by snail-mediated infections.

Faucet Snail Management

Biologists haven’t identified any chemical or biological means of control for the snails yet, so we can only hope that their establishment continues at the slow pace they’ve shown so far. More than likely, though, the invader is just another new long-term resident of the Great Lakes. The best we can do is try to make sure it doesn’t happen again.

We regret that an earlier version of the article failed to properly attribute the map. Much thanks to Anett Trebitz and Val Brady for providing us with the missing information.


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