Changes to shallow subtidal benthic invertebrates following Elwha River dam removal.

Deconstruction of two dams on the Elwha River began in September 2011, resulting in large inputs to the Strait of Juan de Fuca of sediment previously entrained in reservoirs. In the long term, restoration of a natural sediment regime characterized by unimpeded sediment transport from the upper watershed to the lower river and Strait is expected. Annual surveys to assess the response of marine benthic invertebrates to these changes in sedimentation have been conducted since 2011, with some coverage back to 2009. Sites are located along 10 km of shoreline bracketing the river mouth (treatment sites) and 20 km to the east near Green Point (reference sites), and are permanently marked to allow resurveys of the same transects. Divers identify and count individuals \u3e2.5 cm in size (any dimension), and note presence/absence for encrusting taxa. Concurrent vegetation surveys have documented large declines in kelp and other seaweeds since dam removal started. Invertebrate taxa dependent on vegetation have also declined, for example sessile jellyfish (Haliclystus) which attach to vegetation. However, most of the invertebrates surveyed (anemones, tube worms, chitons, clams, snails, crabs, shrimp, sea stars, sea cucumbers, urchins, and tunicates) have not declined to the same extent as seaweeds. Data are currently being analyzed to better evaluate abundance trends for these taxa through summer 2013