PNNL

Abstract

We have been monitoring several restored eelgrass meadows in Puget Sound and in the Northwest, and have found variable success in terms of the systems achieving identified goals. The monitoring has shown (1) early transplant survival is moderate, and no greater than 80% under optimal circumstances; (2) spread of eelgrass transplants is slow, and under optimal (mesocosm) conditions may take 2 years to occur; (3) spread may depend on below-ground organic matter and processes, as well as on grazers and predators; (4) as the meadow matures, plant size may increase as density decreases, indicating that measures in addition to shoot density should be used; (5) higher than normal summer temperatures, seaweed blooms, bioturbator activity, propeller scars, anchor chain drag, and boat wakes may act as cumulative multiple stressors of eelgrass transplants; (6) sites with marginal conditions for eelgrass may support eelgrass in "good" years but may be unsuitable during other years; (7) site assessments and experimental plantings are useful in evaluating a site prior to full transplanting; (8) monitoring should be conducted for at least 5 years following planting to understand long-term sustainability of the system; and, (9) reference sites are critical to interpreting results.