Mussels Bringing Clarity to Maryland Rivers

A single False Dark Mussel

Maryland rivers suddenly less murky after burst in mussel population

Residents along the Severn River are used to muddy, murky water with little visibility below the surface. “You don't have to go out very far before you can't see the very bottom,” said Severna Park resident Nancy Somers.
“Typically this time of the summer, boat traffic keeps it stirred up and very murky looking,” added her neighbor Mel Merritt. “And I've noticed how much clearer it is and how much easier it is to see the bottom of shallow areas.”

What's causing this new, clearer view? Scientists point to Dark False Mussels. They are filter feeders that have blossomed in underwater colonies, covering rocks, docks, pilings and the underside of boats.

False Dark Mussels coat an oyster cage in the Severn River

False Dark Mussels are an invasive species, originally native to the Gulf Coast, and related to the dreaded Zebra Mussel. Should we fear them as well?

Chesapeake Bay Foundation Senior Naturalist John Page Williams said, “They're here when conditions are right for them. I mean they're still here all the time but the population drops way down.” Williams said this shellfish population can be found exploding in the Severn and Magothy Rivers because of our very wet spring. “It's been outrageously wet,” he said.

Dark False Mussels are very small; they’re only about the size of a fingernail. But all together, by the millions, they can make a big impact.
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The clarity the mussels create helps underwater grasses grow which in turn helps fish and the entire ecosystem thrive. But unlike oysters, which are larger, important players in the bay's recovery, Dark False Mussels are much less reliable. They explode in population every several years. For now, locals are loving the view, even if it's not quite the Bahamas.

“It's not a clear blue or Caribbean color but it's much closer to the river I remember from when I was growing up,” Merritt said.

I've seen similar "blooms" of filter feeding organisms that provide, for a while anyway, much clearer water, several times during my time of life in the Bay region. In particular, ten years ago or more, I recall a bloom of the sea grape, Mogula Manhattanensis, that had the visibility in our area as great as 10 ft (1 ft or less is more typical). Such respites are welcome, but don't really represent a long term improvements. The blooms inevitably fail again, and the organisms either die, or are eaten by predators, and the nutrients they have sequestered in their tissues recycled back to the water. For long term improvement we really need large areas covered with relatively stable populations of something long lived, something, like say, oysters.