Great Lakes shipwrecks are facing a threat from an invasive species

Maritime archeologists are fighting to save Great Lakes shipwrecks from a tiny but prolific foe: the invasive mussel.

Zebra and quagga mussels were introduced to the Great Lakes in the late 1980s through ballast water, according to Fisheries and Oceans Canada. They’re similar to each other in their dark brown colours and thumbnail size, but where zebra mussels feed on green algae in shallow waters, quagga mussels live on lake beds up to 100 feet deep and feed on waste.

Renata Claudi is a marine biologist who worked with Hydro One for more than a decade (helping to make power plants resistant to mussel buildup). She says quagga mussels have slowly been overtaking Lake Ontario and its deeper shipwrecks, which is problematic because the mussels cause construction materials to deteriorate faster.

“I don’t think you can put a timeline on it, but it’s a concern,” she says. The speed of deterioration depends on temperature, mussel populations, and the degree of waste in the water.

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Maritime archaeologist Tamara Thomsen, who works for the Wisconsin Historical Society, says Wisconsin divers have been reporting more shipwreck deterioration since quagga mussels took over the Great Lakes. This led the WHS to investigate and collect data from the sites they manage.

In the case of the iron cast S.S. Wisconsin, which sank around 110 feet in 1929, the WHS observed 50 years’ worth of deterioration between 2006 and 2015. Thomsen says they’ve found that metal ships break down faster because mussels add unprecedented weight to the material, creating more stress during currents.

“As these mussels respire, they’re also putting off carbon dioxide, so you end up with these micro-environments of acidification happening under the mussel bed,” she says. “We’re only in the beginning phases of seeing that this is happening. To quantify it is the next step in the research.”

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But Claudi argues quagga mussels present a greater issue than deterioration: obscuring shipwrecks. People often dive down to publicly accessible shipwrecks to appreciate craftsmanship or figure out how a vessel was built. Not only do quagga mussels hide these details, but when a diver attempts to remove the mussels burrowed into wood, there’s a chance the ship could be damaged further. “If the shipwreck disintegrates faster or not is kind of a moot question. At that point you’re not seeing anything anyway,” she says.

Carvings and paint are especially at risk, so Thomsen, who also helps WHS promote shipwrecks as tourist sites, warns divers not to remove mussels. Yet every weekend at least one person brushes them off: “They’re doing it with the best intentions—they want to keep it clean for the next diver—but it really is more of a problem. It’s something that we need to stop.”

Solutions are still being discussed. Claudi says the bacteria Pseudomonas fluorescens, which is “uniquely able to disrupt the digestive system” of quagga mussels, has previously been turned into the biopesticide Zequanox. Though it’s very unlikely to harm any other species or parts of the surrounding ecosystem, it’s “at least 10 times more expensive than chlorine” and would need to be used for six hours straight and applied with a hose to be effective.

Copper sulfate, another one of the mussel’s weaknesses, could also help remove them from shipwrecks. By applying granules to the affected area under a tarp and letting it sit for seven to 10 days, adults would be killed and their shells would slip off.

“I don’t think it’s been tried yet,” Claudi says. “There would probably be some handwringing about putting copper sulfate on the bottom of the lake, but copper ion at low doses acts as a micronutrient.”

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Claudi and Thomsen agree that removing quagga mussels entirely isn’t an option. Even if shipwrecks could be cleansed, the currents would carry more mussels back to the sites every year, so annual treatment is necessary. And there are already an overwhelming number of mussels on the Great Lakes beds.

“If you drained Lake Michigan,” Thomsen says, “it would just be a bowl of quagga mussels with the outline of shipwrecks.”