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Harmful algal blooms (HABs) are dense concentrations of phytoplankton that can have deleterious effects on marine life. We documented two of the largest marine bird mortality events ever definitively ascribed to a single HAB, the cause of which was death resulting from plumage fouling by surfactant-like proteins produced by the dinoflagellate Akashiwo sanguinea. The two mortality events were observed along the coast of Washington State in September and October 2009, collectively representing an estimated deposition of 10 500 carcasses, of which the majority were surf scoters, white-winged scoters and common murres. Each mortality event was coincident in space and time with observed bloom landfall, with each event preceded by a similar chain of environmental conditions. Prior to each event, the presence of A. sanguinea and upwelling-favourable conditions likely led to bloom proliferation. In both cases, this period was followed by conditions that transported the senescent bloom into the nearshore environment, whereupon subsequent wave action lysed A. sanguinea cells, creating foam that contained surfactant-like compounds. This sequence of conditions, exacerbated by the presence of aggregations of marine birds in wing moult, appear to be the necessary requirements for marine bird mortality of this scale due to foam-induced plumage fouling. This mechanism of HAB-induced mortality may become more prevalent in the California Current System given the apparent increasing occurrence of HABs and the broad environmental tolerances exhibited by A. sanguinea.

Acute and chronic risks to aquatic life from exposure to tributyltin (TBT) in surface waters were assessed probabilistically using more than 9 years of monitoring data. More than 50 sites around the United States were sampled, representing six saltwater regions and one freshwater (Lake Erie). Ambient TBT concentrations were compared to acute and chronic effect thresholds to estimate risks for each year (1986‐1988 and 1992‐1996), site type, and region. Site types comprised commercial harbors, shipyards, marinas, and fish/shellfish habitats proximate to these commercial areas. Tributyltin concentrations in surface waters have declined in all regions and site types since passage of the Organotin Antifouling Paint Control Act in 1988. No risks of acute toxicity have been suggested since 1994. Chronic risks have remained highest in marinas compared to other site types but have declined from a risk involving 25% of the species prior to 1989 to one involving 6% of the species in 1996. Risks associated with commercial harbors and shipyards have been similar (4‐6%) since 1994. Chronic risks have been ≤1% in fish and shellfish habitats sampled <1 to 2 km from TBT sources. Risks in Galveston Bay, over all years (1‐19%), have been greater than in the other regions (≤9%).

Abstract-Acute and chronic risks to aquatic life from exposure to tributyltin (TBT) in surface waters were assessed probabilistically using more than 9 years of monitoring data. More than 50 sites around the United States were sampled, representing six saltwater regions and one freshwater (Lake Erie). Ambient TBT concentrations were compared to acute and chronic effect thresholds to estimate risks for each year (1986-1988 and 1992-1996), site type, and region. Site types comprised commercial harbors, shipyards, marinas, and fish/shellfish habitats proximate to these commercial areas. Tributyltin concentrations in surface waters have declined in all regions and site types since passage of the Organotin Antifouling Paint Control Act in 1988. No risks of acute toxicity have been suggested since 1994. Chronic risks have remained highest in marinas compared to other site types but have declined from a risk involving 25% of the species prior to 1989 to one involving 6% of the species in 1996. Risks associated with commercial harbors and shipyards have been similar (4-6%) since 1994. Chronic risks have been Յ1% in fish and shellfish habitats sampled Ͻ1 to 2 km from TBT sources. Risks in Galveston Bay, over all years (1-19%), have been greater than in the other regions (Յ9%).