Oil buried in sediments in the shallow waters of the Gulf is triggering genetic reactions in the gills and livers of local populations of killifish, a ubiquitous prey for marine species vital to the region's economy, according to a study published this week in the review Environmental Science & Technology. Researchers linked those genetic changes to cardiovascular problems, reproductive failures, and weakened and listless offspring.
"The animals are simply not hatching," said Fernando Galvez, an environmental toxicologist from Louisiana State University, who led the study. "The ones that go on to hatch are smaller and have very little vigor."
An otherwise hardy and ubiquitous fish adapted to the shifting conditions of the Gulf of Mexico, the killifish may be signaling a crucial weakness in the maritime food chain three years after the nation's worst offshore oil spill poured more than 200 million gallons of crude into the waters off Louisiana, researchers said. "It's a canary in a coal mine. These guys don't move around much," Galvez said.
"All of those fish we like to eat, eat the killifish," said Andrew Whitehead, an environmental toxicologist from the University of California, Davis who worked on the study.
The researchers analyzed fish and sediments collected from oiled and non-oiled areas of the Gulf shortly after the April 2010 spill and again a year later. Gills were visibly damaged; at the molecular level, they showed sharp increases in genetic signals linked to toxic exposures. Livers showed similar responses.
The data confirmed earlier findings from the LSU researchers and others that residual oil still remains in Gulf sediments, where it serves "as a reservoir of persistent exposure" to marine populations. The researchers also re-created the fish's habitat in miniature and studied the effects of exposure on the reproductive cycle of the fish. Embryos failed to hatch or hatched poorly, and offspring were "listless," Galvez said.
"The adult fish showed exposure long after the oil disappeared (from the water), and the oil in the sediment affected the developing embryos," said Benjamin Dubansky, an LSU toxicologist who also participated in the study.
It may be too soon to conclude what long-term effect the spill has had on the Gulf's fish population, researchers cautioned, but the results appear to parallel the long-term aftermath of the 1989 Exxon Valdez spill in Alaska, which spewed about 11 million gallons and continues to affect maritime species.
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