Scientists Battle to Save Maine's Eelgrass from Destructive Invasive Crab
BRUNSWICK, Maine - The ubiquitous, invasive European green crab is blamed for wreaking havoc on Maine's shellfish populations in recent years, and now it's also suspected of having another negative impact on Maine's marine ecosystem: Researchers suspect that the crabs are responsible for a decline in eelgrass, and they're trying to do something about it.
One experimental eelgrass restoration project is underway in Midcoast Maine.
Simpson's Point in Brunswick lies in an estuary at the upper end of Casco Bay. It's a scenic spot where the woodlands meet the water. Less than five years ago, though, Harbor Master Dan Devereaux says the view was noticeably different, at least at low tide, when eelgrass was visible pretty much everywhere. Now there's hardly any.
"It was around 2011-12 we noticed a drastic decline." Devereaux estimates a 90 percent reduction in Maquoit Bay alone.
Eelgrass, which lies in the shallow waters near the shoreline, is prime habitat for a number of aquatic life forms. So Devereaux decided it was time to act. He got in touch with Dr. Hilary Neckles, a scientist with the U.S. Geological Survey, and a specialist in estuarine and wetland systems. This summer, Neckles launched an experimental eelgrass restoration project - one of on ly two in the state.
I caught up with Dr. Neckles at Simpson's point, where she has come to inspect the handful of eelgrass plants her team planted on the sea bed in July. She points to some buoys out in the bay marking where the plants were put down.
Soon she'll be floating face down, with facemask and snorkel, checking out how much the plants have grown. "I call it stealth monitoring. You just have to sneak up on the plants so you don't disturb the substrate, so that you can see how many plants there are."
The restoration project comes at a time when scientists are also trying to determine how green crabs are effecting eelgrass. Neckles says the green crabs uproot the plants in their search for food - particularly shellfish such as clams and mussels which are buried under the sea floor, or the "substrate," as she calls it. "Big green crabs are foraging in the substrate and they're digging up all this eelgrass, and at the same time they're doing that, they're also increasing the turbidity."
That's because eelgrass is good for absorbing impurities in the ocean, explains Neckles, so when crabs destroy the vegetation they're also depressing the water quality.
Neckles says the speed with which eelgrass declined across the state took everybody by surprise. According to the DEP, eelgrass quantity in all of Casco Bay was down by more than 50 percent by 2013. "It was incredibly sudden on an ecological time scale. It was an acute disturbance and it was caused by the invasive European green crab explosion that we saw in 2012, 2013."
In this part of Casco Bay, Neckles says fewer green crabs have been spotted in the last two years, and there is some eelgrass recovery. But she says there's a long way to go before the plants are brought back to healthy levels. "This is going to take the eelgrass a long time to recover here. So we're testing if can we jumpstart recovery through restoration. Is the water clarity sufficient to permit eelgrass growth?"
One of the difficulties in tackling the green crab problem is the lack of a statewide monitoring program. Numbers have declined in this part of Casco Bay, but just a few miles away in Freeport, Professor Brian Beal, of UMaine Machias, says crab populations are about the same, though Beal, who runs a crab trapping program, says he has noticed a change in size.
"It's just that the animals are much much smaller, and we don't know where the large ones are gone, whether they died or what the story is," Beal says. "But we know there are just plenty of very small ones around, and that's disconcerting."
Meanwhile at Simpson's Point, low tide has come and it's time for Hilary Neckles to zip up her wetsuit and swim out to check on the eelgrass plants. Neckles says the success of this eelgrass restoration project won't be known until next summer, when the final plant measurements are done.
Editor's Note: Later this week, Tom Porter will reveal how one Maine shellfish farmer is dealing with the green crab problem.