Until two years ago, if you had walked down to the shore of Maquoit Bay at low tide, you would have seen a meadow of eelgrass stretching nearly as far as the eye could see across the exposed seafloor. Here near the head of the bay, the sea grass stretched for two miles to the opposite shore, creating a vast nursery for the shellfish and forage species of Casco Bay, of which Maquoit is a part.

Now there’s only mud.

Green crabs took over the bay in the late fall of 2012 and the spring and summer of 2013, tearing up the eelgrass in their pursuit of prey and devouring almost every clam and mussel from here to Yarmouth. Fueled by record high water temperatures in 2012 and a mild winter in 2013, the green crab population grew so huge that the mudflats of Casco Bay became cratered with their burrowing, and much of the Maquoit and adjacent Middle Bay bottom turned into a lunar landscape.

Eelgrass coverage in Maquoit Bay fell by 83 percent. With nothing rooted to the bottom, the seawater turned far muddier, making life hard on any plants or baby clams that tried to recolonize the bay.

“We were astounded,” says Hilary Neckles of the U.S. Geological Survey’s Patuxent Wildlife Research Center, who linked the destruction to the green crabs. “The ecological ramifications really reverberate throughout the ecosystem, because sea grass is the preferred habitat of so many fish and shellfish species.”

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