Cold air snap may have put mussels in jeopardy
BAR HARBOR—Commercial clammer David Dunton knows how to spot the dead bodies. That’s because his livelihood depends on them. And he’s spotted a lot of them after the freezing temperatures of February 3 and 4 when a wind chill on Cadillac Mountain was recorded at minus 62 degrees.
Dunton told the members of Bar Harbor’s Marine Resources Committee, Wednesday, “A tremendous amount of mussels died during the cold snap. Anything that was exposed in the lower part—I’m getting reports that the mussels were deceased.”
Dunton added that the mussels in jeopardy where the ones above the low-water mark and exposed.
According to the Bar Harbor Marine Resources Chair Dr. Chris Petersen, mussels are ectothermic, which means that overall temperature impacts them, not wind chills. Wind chills matter to endotherms like humans, other mammals, and birds. All use metabolic heat production.
Dunton said that between five to seven years ago on Hadley Point, there’d been freezing temperatures, but then there’d been no protective ice. That spring, a month later, the whole bay stunk, he said.
Peterson suggested going out in a couple weeks and looking for the impact of the cold weather event.
“Let’s go analyze the death,” one man said.
According to Petersen, “When people talk about mussels for eating, they are always talking about blue mussels, Mytilus edulis.”
Mussels exist intertidally (as well as subtidally) all over the bay, the best local place to go look is at Hadley Point, he said.
These mussels are harvested three ways in Frenchman Bay, by wild harvesters, and by aquaculture, either by having them grow on ropes or by leasing some subtidal bottom from the state and then seeding the area, and later dragging it.
“The rates of declines we have observed are sobering,” writes Peter S. Petraitis and S.R. Dudgeon in an article for Communications Biology about mussels and other species. “Over the last two decades, abundances of limpets, periwinkles, and dogwhelks have declined by at least 50%…. More alarming is the loss of mussel beds, which we think has been driven by nearly a 16% decline in recruitment per year.”
Recruitment is the process of small and young mussels transitioning to their larger stage of life. It can also mean the time when a species in fisheries is able to be harvested such as when a lobster is the appropriate size.
Petraitis writes, “Our results suggest the effects of climate change on mollusks depend on larval life history. The species with pelagic larvae (mussels and the common periwinkle) are affected by temperature, while species with larvae that are not planktonic (dogwhelks and the smooth periwinkle) or that have a very short planktonic stage (the tortoiseshell limpet) are affected by a combination of factors.”
Those factors include warming, greater salinity and acidification. But for mussels, the warmer ocean impacts how plankton develops. The larvae eat plankton.
The report says that “mussel recruitment is declining by 15.7% per year.”
This, they say, correlates with the increasing temperature of the Atlantic Ocean.
Mussels have already been on the decline in the Gulf of Maine according to a 2017 paper in Global Change Biology by Cascade J.B. Sorte and others, which reads, “The results of these comparisons showed that blue mussels have declined in the Gulf of Maine by .60% (range 29-100%) at the site level since the earliest benchmarks in the 1970s.”
According to the paper, other research shows that from 1960 to 2010, the “southern range limit of established blue mussel populations have shifted by 350 km to the north.” This would be from Cape Hatteras, North Carolina to Lewes, Delaware.
Harvesters pulled close to 4 million pounds of blue mussels ($10 million worth) in 2014. Of those, approximately 85% came from the Gulf of Maine.
Sorte goes on to say, “Therefore, the persistence of mussels within the Gulf of Maine is critical for sustaining both ecological and economic systems, as loss of mussels could precipitate changes in the abundance of interacting species, overall community structure and ecosystem functioning.”
Mussels are a big deal.
According to a 2019 article in National Geographic by Carrie Arnold,
“Mussels are crucial to their ecosystems, both by cleaning water of impurities and creating shelter for other species via their shells (after their decades-long lifespans are over). Although freshwater mussels aren’t edible—they’re tough and taste bad—there are freshwater mussel fisheries that serve an industry for buttons and pearls worth a few million dollars each year in the U.S. What’s more, ecologists estimate the invertebrates provide millions of dollars of services to the environment.”
And though they used to be a defining species, they are now consider a minor contributor, Sorte writes.
The causes aren’t as simple as a one-time big freeze, but, Sorte said, “are likely multifold, including direct and indirect effects of human activities and global change.” That can include species invasion like green crabs, storms, as well as temperature extremes. But she adds that it’s problematic to say what it is that has changed the intertidal community. That’s because there are so many forces occurring making direct and indirect impact.
Petersen said, “Mussels have troubles around here these days.”
Dunton agreed, “Mother Nature can be brutal.”
LINKS TO LEARN MORE
You can see a quick overview of mussel farming here: https://frenchmanbaypartners.org/mussel-harvesting-in-frenchman-bay/
The town’s Marine Resources page.
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