Bunker oil spilled when a 900-foot container ship struck a bridge in San Francisco Bay four years ago wreaked unexpected devastation on local herring populations, annihilating virtually every fish embryo that became exposed in shallow water, according to a new study published this week by a team of 20 California and Washington scientists.

The mortality struck hardest after substances from the refined fuel accumulated within the embryos — and then reacted with sunlight at low tide, the researchers reported in the Dec. 26 edition of the Proceedings of the National Academy of Sciences.

These exposed embryos basically disintegrated in place.

“Based on what we know about the effects of crude oil on early life stages in fish, we expected to find live embryos with abnormal heart function, so it was a surprise to find so many embryos in the shallow waters literally falling apart,” said lead author John Incardona, a toxicologist with NOAA’s Northwest Fisheries Science Center in a story posted here.

"Our research represents a change in the paradigm of oil spill research and detecting oil spill effects in an urbanized estuary," added study co-author Gary Cherr, director of the UC Davis Bodega Marine Laboratory.

The findings — that contact with hydrocarbons from a ship disaster can have astonishingly lethal consequences for developing herring — will come as no surprise to Alaskans.

The Exxon Valdez supertanker grounded on Bligh Reef and spilled at least 11 million gallons of North Slope crude oil into a Prince William Sound on the cusp of spawning season in 1989. The exposure set in motion a complicated chain of ecological and physiological events that scientists believe ultimately sabotaged the health of area herring populations for the next two decades.

Even now, the Sound’s herring are listed as “not recovering” by the Exxon Valdez Oil Spill trustees.

The new San Francisco Bay study “builds on research following the 1989 Exxon Valdez spill (that) … established a new paradigm for understanding the effects of oil toxicity on fish at early life stages,” the authors explained here. “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.”

The California herring catastrophe began when the ship Cosco Busan slammed into the San Francisco-Oakland Bay Bridge on a foggy morning in November of 2007, spilling 54,000 gallons of bunker oil fuel one month before the largest population of herring on the Pacific West Coast began to spawn.

The thick, tarry subsance fouled about 200 miles of coastline, covering an estimated 3,387 acres, including about one third of the herring spawning grounds in the bay. Some 6,849 birds were oiled and killed, and 14 to 29 percent of the 2007-08 herring spawn was ultimately lost, according to the spill website maintained by California Department of Fish and Game.

This fall, the owners and operators of the Cosco Busan agreed to pay $44.4 million to cover government claims, clean-up and restoration, reported the Los Angeles Times here.

In February, 2008 — three months after the spill — the researchers began an experiment. They placed embryos in cages at four oiled and two non-oiled sites, and also began sampling naturally spawned embryos in shallower water impacted by tides.