Questions Remain: How will the oil disaster affect the Gulf’s food web?

While the flow of oil from the Deepwater Horizon has come to an end, millions of gallons of degraded oil and chemicals have the potential to wreak havoc on the ecosystem. If toxic chemical compounds from the disaster impacted eggs and larvae over the summer, biologists say parts of the Gulf could see major changes in its food chain within the next few years.

With an estimated 172 million gallons of oil and 2 million gallons of dispersants put into the Gulf during the disaster, toxins will likely remain in some areas for years. Peter Hodson, PhD, professor in the Department of Environmental Studies and Biology at Queen’s University specializes in fish toxicology and said some of the most concerning compounds are polycyclic aromatic hydrocarbons (PAHs), many of which are highly carcinogenic. While they are metabolized by vertebrates like fish and birds, they can build up in the tissues of invertebrates such as crabs and zooplankton because these organisms can’t excrete them very well.

“There is a big difference when you cross that line between having a backbone and not having a backbone. Invertebrates will build [toxins] up in the tissues but fish can excrete it,” said Hodson.

The fish will eventually feed on those invertebrates and absorb some of the toxic carcinogens but because the compounds are secreted so readily, there is little risk of carcinogenic chemicals working their way high up the food chain.

Nevertheless, the most dangerous impacts are the ones that are less apparent and may not be known for years to come. Martin O’Connell, PhD, an associate professor in the Department of Earth and Environmental Sciences at the University of New Orleans, expressed greater concern over what may have already happened. Because the Gulf oil disaster struck during the height of breeding season for many species, he believes that the toxicity may have had an immediate impact on eggs and larval organisms.

His team will have to collect next year’s data to find out what happened but he’s concerned that some species could show diminished future populations. One of his research crews discovered baby tarpon in the waters near Port Sulphur, Cocodrie and in the Mississippi Sound near Ocean Springs.

“It’s not like populations have been wiped out. There are signs of reproduction but the biggest risk is that we may see dips in populations in some areas years from now. When those [larval organisms and eggs] are supposed to be adults, they just might not be there,” said O’Connell.

Hodson said some of the compounds that were spilled in the Gulf were especially toxic to embryos and while those fish embryos can metabolize and excrete some of the toxins, they can also cause deformities. If toxicity to embryonic fish has already wiped out age classes in some areas, it could ultimately cause complications in the food chain.

“The problem is that those fish influence the species they feed on and also the species that feed on them. You have a whole shift in ecosystem structure and if you knock out those embryos, the effects could be years,” said Hodson.

Doug Inkley, PhD, senior wildlife biologist with the National Wildlife Federation, pointed out that in other disasters such chemical compounds have also been shown to affect everything from appetites to mating behaviors. Those effects could be detrimental to individuals in the population that could affect a whole year class. And when smaller species in the food chain are in low abundance, they can not only impact the next species in the food chain but cause ripple effects.

“If larger organisms further up the food chain were to die from starvation, it could have a very long term impact. There is also competition going on and if you kill of 90 percent of a species, another species moves in and takes its place, those remaining 10 percent may have a very hard time recovering,” said Inkley.

Bruce Stein Ph.D., a conservation scientist with National Wildlife Federation, said that such cascading effects on the food web may be one of the spill’s most lasting impacts. And what makes it so more detrimental is that the impacts may not be fully understood for some time.

“The time lag in detecting food chain impacts will present challenges for devising strategies for recovering and restoring the Gulf’s fish and shellfish,” said Stein.