Deciphering Oil Spill Impacts in a Complex Urbanized Estuary: The 2007 Cosco Busan Spill and Herring Spawning Habitats in San Francisco Bay

On November 7, 2007 the container ship Cosco Busan collided with the San Francisco-Oakland Bay Bridge, spilling 58,000 gal of bunker oil, a mix of residual fuel oil and diesel that powers large vessels. The spill contaminated shoreline along north-central portions of the Bay that provide spawning habitat for the largest coastal population of Pacific herring (Clupea pallasi), a month before the anticipated spawning season. This situation paralleled the Exxon Valdez oil spill, which preceded herring spawning in Prince William Sound and demonstrated the sensitivity of fish early life history stages to the toxicity of crude oil. Prior to the Cosco Busan spill, a major emphasis of our ongoing research program has been the identification of the developing fish heart as a primary target for the sublethal toxicity of polycyclic aromatic compounds (PACs) derived from petroleum, and the development of diagnostic tools for the cardiac impacts of oil exposure in fish. This line of research provided the basis for Natural Resource Damage Assessment studies focusing on cardiac function in Pacific herring embryos in San Francisco Bay for the 2008, 2009, and 2010 spawning seasons. We assessed the impacts of the Cosco Busan spill on herring spawning sites via in situ incubation of laboratory-fertilized embryos in the subtidal zone and sampling of embryos naturally deposited in the lower intertidal zone. Biological effects analyses were coupled with chemical analysis of PACs in embryos as markers of oil exposure. Our findings were both expected and quite surprising, simultaneously ground-truthing years of laboratory study and demonstrating how much more we have to learn about the environmental impacts of oil spills.