Lake Superior's shipwrecks aren't immune to invasive species in the Great Lakes
CBC
Beneath the cold blue waters of Lake Superior lie hundreds of shipwrecks, which serve as underwater time capsules of travel, trade and turbulence dating back more than a century.
While the fate of these structures is largely subject to the hands of time, new foes have crept on board: zebra and quagga mussels.
These invasive species have stirred up concern among archaeologists, historians and divers, who are reporting increased cases of the mussels coating wrecks across the Great Lakes, causing accelerated deterioration.
Ken Merryman, a shipwreck hunter and diver from Duluth, Minn., has been documenting Great Lakes naval relics for 50 years and believes 1,400 shipwrecks known to be in the Great Lakes are collapsing beneath the weight of the mussels – but cites a lack of data as one reason why it's hard to keep track of their decay.
Merryman is using 3D scanning technology called photogrammetry to document the wrecks before they disappear, in hopes of preserving their stories while also making the case to save them before it's too late.
Although most of the damage has been seen within the depths of Lake Michigan, Lake Huron, Lake Erie and Lake Ontario, experts say Lake Superior is no longer immune to the meddlesome mollusks.
Michael Rennie, an associate professor at Lakehead University's biology department in Thunder Bay, has done extensive research on the impact of invasive species on the Great Lakes. He's a Canada research chair in aquatic ecology and fisheries and is also a research fellow with the IISD Experimental Lakes Area.
While zebra mussels have a flat surface along the hinge of their shells, quagga mussels are larger and rounder.
"Wherever zebra mussels have showed up on the Great Lakes, quagga mussels have come in shortly after," Rennie said. "What we find is that zebra mussels are almost entirely replaced by quaggas once they move in."
Zebra mussels were first detected in the Great Lakes in the mid-to-late 1980s, followed by the quaggas. Since their arrival, these invasive species have intercepted a lot of the nutrients that would naturally flow through the Lakes, resulting in a loss of offshore fish, large salmonid species and organisms that can exist in sediments, Rennie explained.
"In some ways, we think that these mussels are actually reshaping the food web of the Great Lakes," he said. "With these mussels moving in, we're actually seeing what seems to be a sort of a wholesale change in terms of how the lake functions."
Northwestern Ontario's lakes tend to have softer water, meaning there's lower levels of calcium, the nutrient necessary for the production of zebra and quagga mussels' shells.
Zebra mussels invaded Lake Winnipeg about a decade ago and efforts to eradicate the species have been in vain, Rennie said.
Now, the mussels are beginning to move into Lake Superior's systems, from Nipigon Bay to the Apostle Islands.