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Blue Mussels in Decline in Gulf of Maine

The Gulf of Maine’s blue mussel population is all but disappearing in the inter-tidal zone, according to ecologists at the University of California, Irvine. The population has declined by more than 60% over the past 40 years.

Ten years ago, before Cascade Sorte became an assistant professor of ecology at the University of California, Irvine, she was a postdoctoral researcher in Massachusetts, where she started to hear rumors about blue mussels.

“So people were seeing blue mussels did not appear to be as abundant as they had once been,” says Sorte.

Sorte decided to conduct a study. She looked at baseline data on blue mussels along the Gulf of Maine coast dating back to the 1970’s, then gathered present-day data. It turns out, those rumors she heard are true.

“Ya know, there are places where the historical studies had counted thousands of mussels in a one meter square plot,” Sorte says, “…and when we went back there, we counted one or two in that same-sized plot.”

Historically, mussels covered up to 70% of the Gulf’s shoreline, which extends from Cape Cod into Canada. Today, Sorte says, they only cover 15%. She chalks up the decline to a few factors: human harvesting, new predators like green crabs – which also plague Maine clams, and temperatures in the Gulf of Maine that are increasing faster than the global average.

Says Sorte, “Some of the physiological studies that my colleagues have done show that they’re [water temperatures]increasing beyond the capacity of the mussels to survive.”

What’s unclear, says Scott Morello, a researcher at the Downeast Institute in Beals, is how much the decline carries over into the ecosystems where mussels are harvested, which are typically soft-bottomed clam flats.

“A lot of those beds have declined over the years, but not all of them,” says Morello. “And they’ve seemingly declined a lot less than the populations on those rocky shores.”

The findings of the University of California Irvine study, Morello says, signal the need for more long-term data. It’s also time, he says, to take a good look at how and where mussels are harvested.

“I don’t think it’s necessarily an issue of unsustainable harvesting,” Morello says. “I think its much more of an issue about lack of knowledge about what’s driving these shifts.”

Sorte and Morello point out that mussels play multiple roles economically and ecologically. Wild mussels seed commercial farms, provide habitat and food for other organisms, and filter ocean water.