{"id":16099,"date":"2025-04-30T12:15:23","date_gmt":"2025-04-30T17:15:23","guid":{"rendered":"https:\/\/uwm.edu\/field-station\/?p=16099"},"modified":"2025-04-30T12:17:48","modified_gmt":"2025-04-30T17:17:48","slug":"16099","status":"publish","type":"post","link":"https:\/\/uwm.edu\/field-station\/bug-of-the-week\/16099\/","title":{"rendered":"A Tale of Two Mussels \u2013 Eight Years Out"},"content":{"rendered":"\n

Howdy, BugFans,<\/p>\n\n\n\n

The BugLady has been curious about the status of Zebra and Quagga mussels since she posted an episode about them in 2016 (\u201cA Tale of Two Mussels \u2013 the One-Two Punch<\/em>\u201d).\u00a0Here\u2019s the original post (slightly tweaked and clarified), with a summary of her recent search of the literature at the end.\u00a0Put your feet up and grab a beverage.<\/p>\n\n\n\n

Spoiler alert \u2013 although there continue to be new articles about these mussels, many are a rehash of older information, and it\u2019s frustrating when agencies do not date their information pages (you know who you are), so it\u2019s hard to say if they\u2019ve been updated.<\/p>\n\n\n\n

2016<\/strong>\u00a0– When the BugLady started researching zebra mussels, it became apparent that the story of this non-native, invasive mussel was inextricably entwined with that of an equally-alien and equally-invasive mussel, the quagga mussel.\u00a0And also that we are, as a species, appallingly slow learners.\u00a0<\/p>\n\n\n\n

Zebra and quagga mussels are in the Phylum Mollusca, a diverse bunch that includes snails and slugs, limpets, clams, scallops, squid, octopi, and cuttlefish.\u00a0Within the Mollusks, they\u2019re in the order Bivalvia, and in the family Dreissenidae.\u00a0<\/p>\n\n\n\n

Zebra mussels (Dreissena polymorpha<\/em>) and Quagga mussels (Dreissena bugensis<\/em>) have traveled far from their native haunts, the Caspian Sea drainage of western Russia, but they have settled nicely into their new homes in America, hitchhiking through the Great Lakes and inland lakes and rivers on boats, boots, bait buckets, and on the feet of waterfowl.\u00a0Zebra mussels were first identified in the US in 1988 in Lake St. Clair, just east of Detroit, and they reached Wisconsin by 1992.\u00a0In 2010, they were found in 130 Wisconsin lakes and rivers.\u00a0<\/p>\n\n\n\n

\"Mussel<\/figure>\n\n\n\n

The first North American quagga mussel was found in 1989, but it wasn\u2019t positively identified until 1991.\u00a0The two mussels are now found in 29 states, and the National Wildlife Federation website estimates that the Great Lakes alone are home to 10 trillion (with a \u201cT\u201d) zebra and quagga mussels.\u00a0They are similarly-marked, but the underside of a Zebra mussel shell is flattened, and a Quagga mussel\u2019s shell is more rounded and doesn\u2019t lie flat.\u00a0Pictures of the two may be found at: Zebra and Quagga Mussels \u2013 Profile | Invasive Species Centre<\/a>.\u00a0Here an animated map of the Zebra mussel\u2019s spread between 1986 and 2024:\u00a0Nonindigenous Aquatic Species<\/a><\/a>\u00a0(the BugLady loves animated maps), and graphics showing the spread of both species in the Lake Michigan basin up until 2015 (scroll down to the Lake Michigan profiles)\u00a0Invasive mussels challenge commercial whitefish fishing in the Great Lakes | Great Lakes Echo<\/a>.\u00a0<\/p>\n\n\n\n

Did they hoof it over here on their own?\u00a0They did not; like most of us, they came over on the boat.\u00a0They undoubtedly arrived in the Great Lakes in the ballast water of ships that ply international waters, as have a rogue\u2019s gallery of hardy gatecrashers (more than 180 species, so far) – a number of North American organisms have been toted to Europe in the same fashion.\u00a0<\/p>\n\n\n\n

Here\u2019s the physics of it: while they\u2019re in their home ports, European vessels take water (plus whatever is swimming in that water) into tanks built on the inside of the ship\u2019s hull, and this \u201cballast water\u201d helps keep the ship upright.\u00a0A ship carrying a small cargo needs lots of ballast, but as it loads more cargo, it discharges ballast water<\/a> (plus whatever\u2019s swimming in it). Ocean-going ships routinely enter the Great Lakes via the St. Lawrence Seaway, and equally routinely, have emptied their ballast water into the Great Lakes.\u00a0In 1993, a difficult-to-enforce law was passed that required incoming ships to replace their home-grown ballast water with ocean water\u00a0before<\/em>\u00a0entering the Seaway,<\/p>\n\n\n\n

In 2011, New York State, gatekeeper for the St Lawrence Seaway, proposed stiff, new regulations about ballast water management\/treatment.\u00a0Three (short-sighted) Midwestern governors pushed back, citing concerns about job loss, even though some innovative alternative transport was suggested at the time.\u00a0<\/p>\n\n\n\n

Zebra and quagga mussels turned out to be plenty adaptable \u2013 although they originated in salt\/brackish water, they quickly adjusted to fresh.\u00a0They are bottom dwellers that live in clusters in great, huge, astronomical numbers on the floors of lakes (at one site in Arizona, quagga mussels number 35,000 per square meter).<\/p>\n\n\n\n

\"Zebra<\/figure>\n\n\n\n

When quagga mussels arrived, they out-competed the zebra mussels.\u00a0Although their life histories are similar, the two mussels prefer different habitats.\u00a0Zebra mussels like water depths of 6 to 30 feet, and quaggas can live as deep as 400 feet, so zebra mussels grow closer to shore, and quaggas thrive through the deep basins of the Great Lakes.\u00a0Quaggas necessarily have a much wider temperature tolerance.\u00a0Zebra mussels prefer hard surfaces to grow on, but Quaggas thrive on softer, siltier lake floors.\u00a0Both species eat all day, but quaggas continue feeding during the winter, when zebra mussels are dormant (you snooze, you lose).\u00a0The BugLady\u2019s photos show them as most people experience them \u2013 as \u201cempties,\u201d cast up on the beach.\u00a0<\/p>\n\n\n\n

Mussels are \u201cfilter feeders<\/em>,\u201d which means that they suck water in through a siphon and run it over their gills.\u00a0Food particles, zooplankton, phytoplankton, and nutrients (and pollutants) are strained out of the water by cilia in the gills and are moved to the mussel\u2019s mouth, and the water is expelled through a second siphon.\u00a0Wastes are released as mucous-covered, organic packets called\u00a0pseudofeces\u00a0<\/em>(vocabulary word of the day).\u00a0An inch-long zebra mussel can filter\u00a0a liter<\/em>\u00a0of water a day.\u00a0One liter per day x Biblical numbers of mussels = large bodies of very clean water.\u00a0<\/p>\n\n\n\n

At first, some people were thrilled \u2013 \u201cYay, the lake is clean again,\u201d shouted the headlines.\u00a0Cities around Lake Erie had been battling pollution in the form of algal blooms due to excessive nutrients (fertilizer) in the water.\u00a0In short order, you could see the bottom of the lake again (it\u2019s called \u201cnutrient bioextraction<\/em>,\u201d and it can be a useful tool in controlled situations where the bivalves are removed when they\u2019re finished eating and processed into animal food or, ironically, fertilizer).\u00a0<\/p>\n\n\n\n

However, the water was crystal clear because there were so few nutrients left in it, and native species that depended on the food in those liters of water were out of luck.\u00a0It was an all-out attack on the base of the food web.\u00a0Zooplankton feed on phytoplankton and are fed upon by larger animals, including tiny fish, which, in turn, feed bigger fish and a variety of other vertebrates.\u00a0But nutrient theft is not the only problem with these mussels.\u00a0<\/p>\n\n\n\n