Mussel Watch Pilot Expansion: an active biomonitoring effort to assess contaminants in the nearshore ecosystems of the Salish Sea

Toxic substances enter Puget Sound from a variety of pathways. Although chemical contaminants in Puget Sound sediments and some biota are monitored on a regular basis, the condition of contaminants in nearshore biota has long been recognized as a monitoring gap. In 2012-13 the Washington Department of Fish and Wildlife, with the help of partners and citizen science volunteers, conducted the first synoptic, Sound-wide assessment of toxic contaminants in nearshore biota. In this study we transplanted native mussels (Mytilus trossulus) from an aquaculture source to 108 shoreline locations along the Salish Sea. Monitoring sites were selected to represent a range of upland land-use types, with percent impervious surfaces (IS%) in adjacent upland watershed units used as a proxy for urban development. The mussels were left on-site for two months and were retrieved in January, 2013. Mussel mortality increased with IS% in adjacent watersheds. There was a significant positive relationship between the concentrations of polycyclic aromatic hydrocarbons (PAHs) in mussels and IS%, with order of magnitude increases in areas of high urbanization (e.g. Elliott Bay, Commencement Bay). In addition, high levels of PAHs were noted near ferry terminals (e.g. Eagle Harbor, Edmonds, and Anacortes). Other persistent organic contaminants (PCBs, PBDEs, DDTs) also showed significant positive relationships to areas of high IS%. Overall, metal concentrations in mussels were relatively low and did not vary greatly from baseline (starting) values. Four out of six metals tested were weakly correlated with IS%; copper, lead and zinc were elevated in areas with relatively high IS%, but mercury showed the opposite trend. These findings suggest toxic contaminants are entering the nearshore food web of the Salish Sea, especially along shorelines adjacent to highly urbanized areas. We recommend that Washington State develop a long-term, regional, nearshore contaminant monitoring program that uses caged mussels as a sentinel species and engages citizen science volunteers to help with monitoring