Eelgrass investment pays off

Under the Clinton ferry dock, sunlight glows through glass blocks to nourish young eelgrass beds recently replanted by a Sequim marine biology firm. - Matt Johnson
Under the Clinton ferry dock, sunlight glows through glass blocks to nourish young eelgrass beds recently replanted by a Sequim marine biology firm.
— image credit: Matt Johnson

Since most people don't often ask about things they cannot see, the eelgrass beds underneath the Clinton ferry terminal have not exactly been a hot topic of conversation for people waiting for a boat.

Biologists and Washington State Ferries management are, however, talking about eelgrass. The aquatic plant, which is a haven and feeding ground for juvenile salmon, is important to the environmental success of the Clinton terminal and dock, which is in the midst of its second phase of reconstruction.

Protected by state wildlife regulations, eelgrass is a concern for many marine construction projects in Puget Sound. At the Clinton dock, a large bed of the plants under the dock forced WSF and the state Department of Transportation to rethink the final dock design. Originally conceived as a much larger structure, the rebuilt dock would have damaged or killed more than 10,000 square feet of eelgrass bed.

But a scaled-down design that included a section of glass block walkway in addition to an aggressive replanting and monitoring program seems to have made the beds healthier than they ever have been.

Ron Thom, a biologist for Battelle Marine Sciences Laboratories in Sequim, said a recently finished study of new eelgrass plantings at the dock show efforts to preserve the plants have worked. Battelle contracted with WSF to restore about 320 square feet of damaged eelgrass, to plant an additional 900 square feet, and to monitor the beds for the next decade. The company has been working with eelgrass at the dock since 1994.

Though he had concerns about the amount of light the new eelgrass would receive and the possibility of oil runoff from cars on the dock, Thom said the past year has been good for the eelgrass planted by Battelle in 2001.

"To date, monitoring shows the eelgrass is doing real well," he said.

Under the dock, which is barren except for the eelgrass and a few clam shells, Battelle's crop is thriving under previously untried conditions. Though WSF put thousands of dollars into constructing a glass-block pedestrian walkway on the dock to allow light through to the eelgrass, engineers and Battelle biologists did not know if it would work. This summer's monitoring, Thom said, proves it did.

Also seeming to work as planned is the oil-water separator intercepting runoff from the dock. Thom said biologists at his company have noticed no eelgrass killoff due to oil runoff.

But as construction workers start tearing down the old, wood half of the dock scheduled for replacement, Battelle and WSF have few innovative ideas for preserving the eelgrass under that portion of the project. While Battelle will replant ruined eelgrass beds after the project is finished, Thom said there may not be a good way to get light under the dock. Glass block will not support the weight of vehicles, he said, and an idea to use metal grating was rejected because of runoff and traction issues.

Dock designers and engineers are still considering solar tubes to light portions of of the dock's underside, Thom said.

Thom said he believes eelgrass will have a healthy future under and around the Clinton dock. Presently, plants are growing at a density double that prior to dock construction.

In all, WSF and the DOT expect to spend about $27 million to rebuild the Clinton dock and terminal. When it is is finished in mid-2003, the concrete and steel dock will have three ferry slips, as opposed to the two available at the old wooden dock.

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