The study builds on research following the 1989 Exxon Valdez spill, which released up to 32 million gallons of crude oil into the comparatively pristine environment of Prince William Sound, Alaska. That research established a new paradigm for understanding the effects of oil toxicity on fish at early life stages.
The new study suggests that this old paradigm is inadequate to explain the dramatic, lethal effects of very low levels of oil on fish embryos, even in an urban estuary with preexisting background pollution.
"Based on our previous understanding of the effects of oil on embryonic fish, we didn't think there was enough oil from the Cosco Busan spill to cause this much damage," Cherr said. "And we didn't expect that the ultraviolet light would dramatically increase toxicity in the actual environment, as we might observe in controlled laboratory experiments."
Researchers began the new study in February 2008. They analyzed the levels of oil-based compounds in caged herring embryos at four oiled and two non-oiled subtidal sites, all of which were at least 1 meter below the water's surface. Naturally spawned embryos from shallower sites were also analyzed.
Three months after the spill, caged embryos at oiled sites showed nonlethal heart defects typical of oil exposure.
But embryos from the shallower, intertidal zone not only exhibited the nonlethal heart defects, they also showed surprisingly high rates of dead tissue and mortality unrelated to heart defects.
"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.'/>"/>
|Contact: Gary Cherr, UC Davis Bodega Marine Laboratory|
University of California - Davis