Scientists Diving for Answersby Cassandra Profita
The Daily Astorian, July 4, 2008
Transplanting eelgrass may help crab, salmon
Scientists don't know a lot about why eelgrass grows in certain underwater environments and not others.
They do know the aquatic plants provide valuable shelter for juvenile salmon and Dungeness crab and attract a buffet of critters for them to eat.
To study the possibility of growing more eelgrass in the Columbia River estuary, researchers with the Pacific Northwest National Laboratory have developed models detailing the current locations of eelgrass beds and the places where light, salinity and current conditions would support eelgrass growth.
"The model tells us where eelgrass could potentially grow based on limited information," said Amy Borde, a marine biologist with the national lab. "There really hasn't been a lot of research done on eelgrass in the estuary. Where is it growing and where isn't it growing and why?"
To test the model, divers working with the lab suited up last week and dove down to the bottom of Youngs Bay, Baker Bay, near Ilwaco, Wash., Trestle Bay, near Hammond, and the waters around Desdemona Sands to harvest healthy eelgrass beds and sow new beds in areas where eelgrass isn't growing.
The harvested shoots were bundled in groups of four in the Hammond Boat Basin, loaded 120 at a time onto metal plates then replanted underwater.
The new beds will be monitored over the next 12 months to see if they take root and attract juvenile crab.
Curtis Roegner, a marine biologist at the National Oceanic and Atmospheric Administration's Hammond Research Lab, will be testing to see if crab are using the new eelgrass beds over the next year.
"The hypothesis is we'll find higher abundance of crab around eelgrass than on bare sediment," he said.
He'll put out traps in the new eelgrass beds, as well as in older, more established beds and non-eelgrass habitat and take stock of the number and size of the crab he catches.
Money for research
Bonneville Power Authority provided $250,000 to allow researchers to model potential eelgrass turf in Puget Sound and the Columbia River estuary, plant new beds and study the new plantings.
A lack of documentation makes it hard to know the historic range of eelgrass in the estuary.
"Typically in estuaries around the world, there was more than there is now," Borde said.
In other parts of the world, eelgrass beds have been declining because of development and poor water quality.
Some waterfront development in Puget Sound has been curbed to protect eelgrass under Washington's "no net loss" policy for the plant.
Eelgrass is sensitive to light, salinity and current, and because suspended sediment clouds Columbia River water, it can't live very deep in the estuary. Dredging stirs up and eliminates some potential eelgrass grounds, and structures such as docks can block the light eelgrass needs to grow.
Roegner said the higher, channelized flow of the Columbia River is not conducive to eelgrass growth.
"We see it in more protected areas," said Roegner. "Too much current works it out of the sediment."
Borde said eelgrass could also be limited by recruitment, or the ability to spread seeds into areas where they can take root and grow.
So far, the research she's done with Ron Thom, a staff scientist with the national laboratory, has shown a few of the eelgrass plants in the estuary are producing seeds.
"We haven't seen a single flowering shoot in all of our plantings," Borde said. "There are a lot of unknowns. ... If we put the plants in and they do well, it will show the plants can live here, and we can do more and expand the area."
The hydrology of the Columbia has changed dramatically since dams were installed upriver, and the jetties at the mouth have changed the river's topography.
Micah Russell, executive director of the Columbia River Estuary Study Taskforce, said those changes actually make the estuary a more inviting place for eelgrass to grow.
"We suspect that the conditions for eelgrass have improved since installation of the dams because the salt wedge is able to intrude farther into the estuary during the summer than would normally occur," he said. "Even though we don't see it everywhere now, the chemistry and water quality issues that make life suitable for eelgrass are better now."
Thom said taking eelgrass from the estuary for replanting will ensure the new populations are adapted for the volatility of the Columbia River.
Even though it can't make up for the loss of marsh and swamp habitat in the estuary, Borde said, expanding the eelgrass beds should still help fragile populations of out-migrating juvenile salmon.
"This would help offset some of those losses even if it's not exactly the same habitat. It provides sheltered habitat and eating areas," she said. "The ultimate goal is flourishing habitat."
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