The 2007 Cosco Busan disaster, which spilled 54,000 gallons of oil into the San Francisco Bay, had an unexpectedly lethal impact on embryonic fish, devastating a commercially and ecologically important species for nearly two years, reports a new study by the University of California, Davis, and the National Oceanic and Atmospheric Administration.
The study, to be published the week of Dec. 26 in the early edition of the journal Proceedings of the National Academy of Sciences, suggests that even small oil spills can have a large impact on marine life, and that common chemical analyses of oil spills may be inadequate.
"Our research represents a change in the paradigm for oil spill research and detecting oil spill effects in an urbanized estuary," said Gary Cherr, director of the UC Davis Bodega Marine Laboratory and a study co-author.
On the foggy morning of Nov. 7, 2007, when the container ship collided with the San Francisco-Oakland Bay Bridge, bunker oil contaminated spawning habitats for the largest U.S. coastal population of Pacific herring—a month before spawning season.
The new study, which analyzed Pacific herring embryos following the spill, highlights the effects of bunker oil on fish embryos in shallow water, the potential significance of sunlight interacting with oil compounds, and the extreme vulnerability of fish in early life stages to spilled oil.
Specifically, the study found that components of Cosco Busan bunker oil accumulated in naturally spawned herring embryos, then interacted with sunlight during low tides to kill the embryos. Laboratory fertilized eggs, caged in deeper waters, were protected from the lethal combination of sunlight and oil, but still showed less severe abnormalities associated with oil exposure.
Crude oil is naturally occurring, liquid petroleum. Bunker oil is a thick fuel oil distilled from crude oil and burned on ships to fuel their engines. It is contaminated with various, sometimes unknown, substances.
"These embryos were literally falling apart with high rates of mortality," said Cherr.
In 2008, almost no live larvae hatched from the natural spawn collected from oiled sites.
The high death rates did not seem to be caused by natural or manmade causes unrelated to the spill, the researchers report. No toxicity was observed in embryos from unoiled sites, even those near major highways.