A minnow considered the canary in Louisiana’s coastal ecosystem can’t shake the hydrocarbon cough it picked up when BPs oil started washing ashore three years ago.
Recent studies on new generations of the Gulf killifish, a marsh minnow diagnosed with signs of oil poisoning in 2010, shortly after the Macondo blowout began, confirm that hydrocarbon toxins remain in marsh sediments and continue to cause biological impairments that were precursors for species-wide collapses in Alaska after the Exxon Valdez spill.
The results have no implication for seafood safety because the levels of toxins detected are well below those considered hazardous for seafood consumption, the researchers said.
While the killifish is best known locally as the “cocahoe minnow,” a bait fish favored by anglers, researchers consider it the equivalent of the proverbial canary in a coal mine, a keystone species in the food chain that can give early warnings of problems for the entire system.
Andrew Whitehead, who in 2010 led an LSU team studying adult killifish from heavily oiled areas of Barataria Bay, said at the time, “We were detecting cellular responses to toxins that are predictive of impairment of reproduction and embryo development.”
Now, follow-up lab research on killifish embryo have confirmed those fears.
The research team exposed one group of embryo to sediments collected from heavily oiled areas of the bay and another group to sediments from areas that were not impacted.
“We know that early life stages, especially in fish, are very sensitive to the effects of oil, and we know that many animals (in the Gulf ) use these estuaries for the early stages of life and will be exposed to these sediments,” Whitehead said. “So we wanted to bring the research into the lab with a control group to see what the results would be, especially more than a year later.”
The embryos exposed to uncontaminated sediments showed no abnormalities, but those exposed to the oil-impacted sediments displayed many of the same developmental impairments detected in the adult fish during the first project, researchers found.
“They had the same hallmark signature impacts of cardiovascular toxicity as the adults,” Whitehead said. “There was an accumulation of fluid around the heart, depressed heart rates and decreased hatching success.”
The researchers were looking for signs that the embryos were impacted by polycyclic aromatic hydrocarbons (PAHs), components of oil that are known carcinogens and that can persist for more than 50 years in ecosystems hit by oil spills. As in the first study, the levels recorded in this project were either trace or “undetectable” — the term used when a toxin does not register in water samples but animals exhibit biological responses that are symptomatic of exposure.
The responses shown by killifish embryos to such low levels of PAHs reinforced concern that trouble could be waiting down the line for economically more valuable species.
Whitehead, now at the University of California at Davis, said the concern wasn’t about the toxins accumulating in predators such as speckled trout and redfish that consume killifish, but that long-lasting PAHs could have biological impacts that may show up in future generations of a whole range of creatures that live close to and on the marsh bottom, such as shrimp, crabs and oysters.
“A lot of the (PAHs) have sunk into sediments in the marshes in Barataria Bay and get redistributed into the water column every time it gets windy,” he said. “So all animals that use shallow water in these estuaries will be exposed.”
A cause for hope, he said, is that only a handful of places across the vast Louisiana coast were heavily hit by the oil. That could mean large populations of killifish and other species were unaffected.
“So the hope would be animals that inhabit areas that were not heavily hit will be able to provide unaffected populations that can buffer the harm done in the affected area,” Whitehead said.
“Of course, we don’t know that, and that’s why we need to continue to monitor this.”
Whitehead repeated a concern voiced in 2010 that enough research should be done on the biology of the species being examined rather than just their safety for human consumption.
“As these studies show, you can have levels of these toxins that are no threat to humans, but can cause serious problems for a whole range of animals living in the ecosystem with just a very small level of contamination,” Whitehead said. “I haven’t seen a whole lot of research published on the biology of animals post-spill. That concerns me.”