Mussels Missing or Merely Migrating?
- Melissa Waterman
- Jul 31
- 2 min read
By Melissa Waterman
Where have all the mussels gone? That’s a question which has troubled researchers around the Gulf of Maine for the past decade. Blue mussel beds were once easily found in the intertidal zone from Massachusetts to Nova Scotia. Mussels are considered a bellwether species for the Gulf — their presence indicates that all is well in the greater Gulf ecosystem.
Blue mussels. GMRI photo.
When the beds disappeared, scientists were worried. A study published by the University of California Irvine in 2016 found the Gulf’s mussel population had declined by 60% over the previous 40 years. Multiple factors — increased Gulf water temperatures, green crab predation — combined to cause the intertidal mussel beds to shrink and then vanish.
Were the mussels really gone? “We were only looking in the intertidal zone,” said Aaron Whitman, a senior research associate at the Gulf of Maine Research Institute (GMRI) in Portland. “There’s always been some subtidal mussel beds.”
Researchers believe that mussel beds have been moving from the intertidal zone to the subtidal zone (the subtidal zone is below mean low tide and is rarely exposed). “There’s lots of pressure on the mussels to go deeper to escape green crabs and heat,” Whitman said. The mussels find a refuge in the subtidal areas, creating beds that a casual observer might not be able to see.
Whitman is involved in GMRI’s mussel bed mapping project. The project asks the public to take pictures of the subtidal mussel beds that are visible at extreme low tides. Using these photos as guides, Whitman and colleagues can acoustically map the mussel beds and track any changes to the beds over time. Acoustic equipment is used to identify different bottom types, distinguishing mussel beds from other types of seafloor bottom.
He uses maps of mussel beds made by the Department of Marine Resources in 2010 as a baseline for comparison to those created through GMRI’s project.
“There were beds on the northern side of Mackworth Island [in Casco Bay] in 2010. There are none there now,” he said. “On the southern end there’s the biggest bed in Casco Bay that I’ve seen, and we stumbled on it at extreme low tide.”
The mussel bed mapping project is largely concentrated in Casco Bay, however groups have sent pictures of subtidal mussel beds exposed at extreme low tide from Rye, New Hampshire to West Bath as part of the project. The project’s web page (https://gmri.org/projects/mussel-bed-mapping/) gives the precise dates for extreme low tides throughout the summer, allowing those interested in participating to plan ahead.
“Finding these beds is important because they create an environment for other species to thrive and are food for lots of species,” Whitman said. “Mussels are great indicator species and a great resource. The only thing we can do is go out and look for them.”
This article was made possible with the support of Farm Credit East Ag Enhancement grant
It's intriguing to think about the possible reasons behind the mussels' disappearance. The Gulf of Maine's ecosystem is complex, and changes in mussel populations could signal broader environmental shifts. For more in-depth information on the incremental changes affecting marine life, including mussels, you might find scritchy scratchy's coverage insightful.
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