When the Exxon Valdez ran aground in Alaska's Prince William Sound, it unleashed a regional catastrophe whose effects continue to play out these two decades later. One such apparent effect was the subsequent collapse of the region's herring.
Now we have a new study of herring, but after a different spill in a different place. Four years ago, in November, 2007, a container ship called Cosco Busan hit the San Francisco Bay Bridge, and spilled over 50,000 gallons of bunker fuel-oil into San Francisco Bay. Twenty researchers teamed up to tell us what happened in the next four years to one important species of fish: herring. The result is a study titled, "Unexpectedly high mortality in Pacific herring embryos exposed to the 2007 Cosco Busan oil spill in San Francisco Bay," published in the journal Proceedings of the National Academy of Sciences. (December 27, 2011, doi: 10.1073/pnas.1108884109).
The 2007 Cosco Busan spill oiled shorelines near the shallow-water breeding habitat of the West Coast's largest population of Pacific herring -- which supports the last remaining commercial finfish fishery in San Francisco Bay. (Pacific herring lay sticky eggs on near-shore seaweed and rocks.) The scientists compared the health of herring embryos from oiled and un-oiled parts of the Bay. They looked at embryos from natural spawning and embryos held in special underwater cages.
The spill happened right around the start of herring spawning. Three months after the spill, wild embryos from shallows along the oiled shorelines showed "unexpectedly high rates" of dying tissue; most of them died. Those a bit deeper in cages near the oiled sites didn't die as much, but they had heart problems including, "arrhythmia, silent ventricle, severe bradycardia, minimal overall contractility, and loss of heart beat." Loss of heart beat is a problem. At the un-oiled sites, the baby herring, wild and caged, showed no such problems.
In studies following the Exxon Valdez disaster, and in laboratory studies, scientists have found that fish embryos exposed to oil develop abnormalities of their jaws and body axis, and swelling (edema) involving their heart and their yolk sacs. Even very small amounts of petroleum's most abundant polycyclic aromatic compounds interfere with embryonic heartbeat. Embryos with edema tend to die, but scientists found that fish embryos surviving exposure to Alaska North Slope crude oil grew into adults with subtle abnormalities in heart shape and swimming abilities.
Under the microscope, embryos from San Francisco Bay show stark differences between oiled and un-oiled sites. Eggs from un-oiled sites are transparent and plump as grapes, their inner embryos curled around bright, transparent yolks. The oiled ones are a mess; the egg-clusters look dim and deteriorated, the individual eggs ruptured, mainly dead. Oil-exposed embryos examined in more detail show skin problems.
In 2008, the year after the San Francisco spill, "essentially no live larvae hatched" from oiled sites. By 2010, herring embryos from oiled sites still had some heart problems, but the scientists didn't find any oil-related death; hatch rates at oiled sites matched those at un-oiled sites. (Un-oiled is a relative term, since--unlike Prince William Sound, Alaska -- San Francisco Bay is an urbanized place; the water always contains chemicals from petroleum and industry. But the difference in herring embryo survival from oiled and un-oiled sites, and the recovery in the years following the spill, shows that San Francisco Bay's everyday pollution levels weren't killing the herring -- the oil spill was.)
The scientists were not surprised at the levels of oil-related chemicals (called polycyclic aromatic compounds) in the water at oiled sites. But they were surprised that herring embryos died at the low concentrations of those chemicals that they found in the herring's flesh the next year. In their words, they found, "an unexpectedly severe (i.e., lethal) form of developmental toxicity." They initially thought those levels were too low to kill the fish.
So, why did embryos die at relatively low chemical levels in 2008? It appears that bunker fuels and other petroleum products contain chemicals that become more toxic when exposed to sunlight. Chemical levels that would not kill fish in the absence of ultra-violet light, do kill fish after exposure to sunlight. (Apparently, exposing the chemicals to ultraviolet light causes reactions that produce forms of oxygen that damage living membranes. Chemistry is complicated.) That seems to be why the embryos in the cages, deeper and more distanced from sunlight, did not die at the same rate as the embryos in the shoreline shallows.
Among the things the authors want emphasize is this: "the exceptional vulnerability of fish early life stages to spilled oil."
What might this mean, then, for the Gulf of Mexico and every other place where oil gets spilled? The Deepwater Horizon blowout in the Gulf of Mexico did not seem to cause mass fish-kills. But my next concern was, "What will happen in the next few years to the fish and shrimp eggs and larvae?" The mass die-off of newborn dolphins in the Gulf of Mexico in the winter of 2011 seemed an ominous reminder that adult survival does not guarantee good reproduction. (For my journal article on the Gulf blowout, see here. For my book on the Gulf blowout, see here.) In the first four months of the blowout, a team of researchers found various sub-lethal effects in killifish from the Gulf (http://bit.ly/vh7AUl; full citation at end of this article). "Though the fish may be 'safe to eat' based on low chemical burdens in their tissues, that doesn't mean that the fish are healthy or that the fish are capable of reproducing normally," lead researcher Andrew Whitehead told Mother Jones (http://bit.ly/nYPln1).
There's also some informed guesswork on plankton in the Gulf in a recent article in Oceanography. And there's a bit of relevant Gulf of Mexico data in another study that suggests Gulf fishes may have dodged a bullet in year one. But to really know the longer-term effects will require a few years and a little hindsight.
For more than two decades of hindsight, we can turn, again, to Exxon Valdez. During the months following the Exxon Valdez spill, herring eggs and larvae in oiled areas of Prince William Sound died at twice the rate they did in un-oiled areas. Larval growth rates were half those measured in other North Pacific populations. Herring larvae also suffered malformations, genetic damage, and grew slower than ever recorded anywhere else.
Those problems were gone by the following year.
But it's not that simple. Different things get hurt at different rates for differing periods of time. Oil that works its way into sediments and under boulders remains toxic and available to living things. In Prince William Sound after Exxon Valdez, oil hiding beneath mussel beds continued to find its way into the region's animals and their food web. For years, ducks and otter suffered chronic exposure to oil. For at least four years, eggs of pink salmon, which spawn in lower reaches of streams near seawater, died at abnormally high rates. Young sea otters born for several years after the spill survived at unusually low rates. After sea otters had received protection from hunting for their fur, their population increased 10 percent annually, but after the oil spill, in heavily oiled areas their numbers did not increase for at least a dozen years. Shellfish--which sea otters (and people) eat--concentrate oil hydrocarbons quickly and metabolize them slowly. For at least several years, birds called black oyster catchers fed their chicks more mussels but achieved less growth than normal. For many years, harlequin ducks (perhaps the world's most exquisitely beautiful sea duck, which is saying something) suffered low weight as their bodies tried to fight the toxic effects of petroleum hydrocarbons they were getting in their food. In parts of Prince William Sound, they were dying at rates of 20 percent annually for over a decade. A study published in the April, 2010 issue of Environmental Toxicology and Chemistry found that Harlequin Ducks are still ingesting Exxon Valdez oil. Biopsy samples showed their livers containing the enzymes they produce when their body is wrestling with oil. The authors of that study concluded, "This adds to a growing body of literature suggesting that oil spills have the potential to affect wildlife for much longer time frames than previously assumed." (See end of this piece for references to above facts.)
Meanwhile, in just the month I'm writing: Shell has spilled at least 1.7 million gallons of oil off Nigeria. (And according to the U.N., "Nigeria could prove to be the world's most wide-ranging and long term oil clean-up exercise ever undertaken if contaminated drinking water, land, creeks and important ecosystems such as mangroves are to be brought back to full, productive health;" That's a big "if."). Meanwhile, Shell had to shut down a leaking rig in the Gulf of Mexico. Meanwhile, in a situation with disturbing parallels to BP's 2010 Gulf blowout, Brazilian government prosecutors are seeking $11 billion in damages from Chevron for a still-leaking well drilled by Transocean, the same company that was drilling BP's well in the Gulf of Mexico before the blowout destroyed its Deepwater Horizon rig. Meanwhile, oil is leaking from a tanker in France. Meanwhile -- that is just a little of this month's current events.
And also meanwhile, amidst all this spilled and leaking oil, India is exploiting the dropping prices and increasing efficiencies of solar panels to fulfill it very ambitious energy plans. Solar generated electricity now costs Indian consumers about the same amount they pay for oil-generated electricity. And the price gap between solar and coal is narrowing. These comparisons, says Cédric Philibert, a senior analyst at the International Energy Agency in Paris, are "becoming better and better every month." That's the future. It has to be.
Selected Additional References:
Sublethal effect in Killifish from the Gulf: Whitehead, A., et al., "Genomic and physiological footprint of the Deepwater Horizon oil spill on resident marsh fishes," Proceedings of the National Academy of Sciences, 26 December 2011. DOI:10.1073/pnas.1109545108.
Effects of oil on fish eggs and larvae: Joanna Burger, Oil Spills. New Brunswick,
NJ: Rutgers University Press, 1997.
Herring egg and larval mortality following Exxon Valdez: M. D. McGurk and Evelyn
D. Brown, "Egg-Larval Mortality of Pacific Herring in Prince William Sound,
Alaska, After the Exxon Valdez Oil Spill," Canadian Journal of Fisheries and Aquatic
Science 53, no. 10 (1996): 2343-54.
See also B. L. Norcross et al., "Distribution, Abundance, Morphological Condition, and Cytogenetic Abnormalities of Larval Herring in Prince William Sound, Alaska, Following the Exxon Valdez Oil Spill," Canadian Journal of Fisheries and Aquatic Science 53, no.10 (1996): 2376 -87.
See also J. E. Hose et al., "Sublethal Eff ects of the Exxon Valdez Oil Spill on Herring Embryos and Larvae: Morphological, Cytogenetic, and Histopathological Assessments, 1989-1991," Canadian Journal of Fisheries and Aquatic Science 53, no. 10 (1996): 2355-65.
Different things get hurt at different rates: C. H. Peterson et al., "Long-Term
Ecosystem Response to the Exxon Valdez Oil Spill," Science 302, no. 5653, December
19, 2003: 2082-86.
Harlequin Ducks still ingesting Exxon Valdez oil: Esler D., et al., "Cytochrome P4501a Biomarker Indication Of Oil Exposure In Harlequin Ducks Up To 20 Years After The Exxon Valdez Oil Spill," Environmental Toxicology And Chemistry 29, no. 5 (2010): 1138-1145, DOI: 10.1002/etc.129.
See also: S. Dhillon, "Exxon Oil Showing Up in Alaskan Wildlife 20 years After Spill, Research Shows," Canadian Press, April 14, 2010.