54,000 gallons of spilled bunker oil can be enough to devastate a commercial herring population

Such an oil spill, which occurred during the 2007 Cosco Busan collision (container ship vs bridge) in San Francisco Bay, is (supposed to be) peanuts compared to for instance the 1989 Exxon Valdez’s 32,000,000 gallons of crude, or the BP Gulf spill of 2010 – which released an estimated 53.000 to 68,000 barrels per day – for 5 months on end.

But to local ecology that can be a very poisonous peanut, new research shows.

oil spill herring contamination San Frasisco Bay
Last week a group of scientists from NOAA and the University of California in Davis published their analyses of the ecological consequences of the oil spill in PNAS.

The bunker oil that leaked away from the damaged vessel contaminated the spawning grounds for the largest population of Pacific herring along the US coast. Components of the oil were found in caught herring embryos and even eggs. Many fish died and others showed abnormalities.

Several months after the spill on different sites around the bay live fish were found to have developed heart defects that are commonly associated with oil contamination – and to carry around dead tissue, also likely as a consequence of water pollution. In the year 2008 ‘almost no live herring larvae’ hatched from the spawning grounds, the researchers say.

Based on previous understanding of the ecological effects of oil spills, as for instance the Exxon Valdez disaster in Alaska, the researchers had not expected this comparatively small oil spill to create so much damage.

Different factors determine ecological damage oil spills

They conclude it is not just the amount of oil that matters, but also the type of oil. Thick bunker oil for instance can contain more chemical pollutants than normal crude oil.

Moreover local climatic effects can influence the damage as well. Normally a cold Arctic climate is thought to be the worst to have an oil spill, as the low temperatures hinder the breakdown of oil – and therefore environmental damage can continue for years on end. In case of the BP oil leak in the Gulf of Mexico much apparently depended on a combination of water oxygen levels and the availability of other nutrients – both of which factors determine the amount of bacterial breakdown of methane and oil.

In the case of the 2007 San Francisco Bay oil spill though the environmental damage unexpectedly increased due to sunlight exposure. Within oil-contaminated herring embryos swimming around in the shallow waters during spring this sunlight led to the formation of other toxic chemicals.

“Bunker oil contains the chemically uncharacterized remains of crude oil refinement, and one or more of these unidentified chemicals likely interacted with natural sunlight in the intertidal zone to kill herring embryos. This reveals an important discrepancy between the resolving power of current forensic analytical chemistry and biological responses of keystone ecological species in oiled habitats.”

© Rolf Schuttenhelm | www.bitsofscience.org

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