Invasive eelgrass doesn't follow the usual invader's script

Jun 16, 2011

WILLAPA BAY, Wash. – The usual story of invasive species goes something like this: An exotic plant or critter hitches a ride on an incoming cargo ship. Alarm bells go off. An eradication campaign starts. But now there's a non-native seaweed on the West Coast that breaks the mold. Japanese eelgrass has defenders along with its critics.

Willapa Bay produces more shellfish for Northwest tables than any other inlet on the West Coast. Brian Sheldon's family has been growing clams and oysters on the tide flats here for three generations.

"These little holes here are all clams," Sheldon explained. "I call this my college fund bed. I tell my kids, you go out and work that bed, because that's how you're going to college."

But Sheldon jokes that's shaping up to be an inexpensive state school rather than a plush private college the way things are going. His clam beds should be bare sand. But Sheldon shows how his acreage is being overrun by a green sea grass that really belongs on the other side of the Pacific.

"It just takes a little bit of heat and little bit of good light and this stuff starts to go. And, oh boy! In the summer, this piece of ground here will be completely covered with grass," Sheldon said. "It kinds of sits in there and holds the heat in there in the bed and it makes the clams watery and weaker."

Sheldon says the "infestation" has reached "devastating" proportions. Several neighboring companies have simply abandoned some clam beds.

"Our yields are down 40 to 50 percent, you know."

Invasion is decades old

Marine biologists believe the Asian eelgrass was most likely brought to Washington decades ago in shipments of oysters from Japan. The plant is also called Japonica or dwarf eelgrass. It has since spread north to British Columbia and south along the Oregon coast into California.

Shellfish growers want Japanese eelgrass declared a noxious weed so they can spray herbicide or mow the invader down. California has already done so.

To the growers, it seems obvious that Washington and its neighbors should follow. The sea grass is not native. It's causing a nuisance and there are control methods that work.

Surprising positive side

But not so fast argue some marine scientists, state agencies and conservationists.

"In most areas of the world, these plants are highly protected," said Sandy Wyllie-Echeverria, a marine biologist with the University of Washington. He added:

"So in my mind, the ledger needs more examination. There are areas where Japonica (the scientific name) has been shown to be a valuable resource and there are other areas where it is quite mixed."

In the Northwest, he says waterfowl like to eat the sea grass. A suite of smaller creatures probably lives and feeds among it. The eelgrass might also stabilize eroding beaches.

The Sierra Club's Laura Hendricks says her group opposes eradication of the inadvertent colonist, even though it's non-native.

"For two reasons: One, it is fish habitat. But more importantly, in their efforts to eradicate Japanese eelgrass there is a very high probability they could be eradicating native eelgrass. That is something that would have a major impact on recovery of our fish species and the birds."

What to do?

Caught in the middle is the Washington State Noxious Weed Control Board. The panel's director, Alison Halpern floats a possible compromise: list Japanese eelgrass as a noxious weed on commercial shellfish beds only.

"It might not be the end-all, be-all solution that either side is looking for but what it does do is allow us to acknowledge it is a problem in one area, but it is not considered a problem in the other areas."

Halpern's gotten some positive feedback, but not everyone's on board yet. Shellfish growers say it's a good start, but worry the plan could require them to fight the non native sea grass in perpetuity.

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