Long-term impacts of the oil spill will not be known for years: After the Exxon Valdez spill in Alaska, it took three years before the local herring fishery collapsed. "A lot of species were spawning during the Deepwater Horizon [spill]," notes biological oceanographer Edward Chesney of the Louisiana Universities Marine Consortium (LUMCON). "We undoubtedly lost a lot of those fish and egg larvae—they can't move and are highly vulnerable to oil toxicity." The loss of entire generations of young marine life may also propagate up the food chain—over time. Already, scientists have found evidence of oil passing into plankton (pdf), which serve as the broad base of the food web.
Impacts to marine life range from outright death to reduced reproduction, altered development, impaired feeding as well as compromised immune systems. Even exposure to low concentrations of oil that fish embryos survive can alter the shape of their hearts as adults and reduce their ability to swim, according to research published April 11 in Proceedings of the National Academy of Sciences.
And simply because scientists had little information on certain species before the spill—such as the denizens of the deep that bore the brunt of the dispersed oil—its impacts may prove impossible to measure, although research continues into the array of nematodes, fungi, mollusks and other organisms that thrive on the seafloor. "We don't have a lot of information on deep water species in general," Chesney notes.
What is clear, however, is that the approximately five million barrels of Lousiana sweet (low-sulfur) crude that spewed into the Gulf of Mexico was toxic—a toxicity exacerbated by the use of 1.8 million gallons of dispersant both in the deep sea and at the surface. The oil itself sports an array of so-called polycyclic aromatic hydrocarbons (PAHs)—benzene, toluene and the like that are known to cause cancer. NOAA testing found more than 800 oil-related compounds in the water during the spill. "Those components are very toxic," says toxicologist Scott Miles of Louisiana State University. "Those are the ones you're sniffing when filling up the gas tank."
At the same time, they are compounds that fish and other organisms are efficient at not taking up into their tissues. "Accumulation of PAH is very difficult," notes toxicologist Joe Griffitt of the University of Southern Mississippi, who is studying how oil exposures that do not kill an animal can affect its reproductive success.
And these different compounds have different effects, some of which cancel each other out. "You have a very complex situation, very quickly," says Griffits. PAH can have impacts that don't kill the marine organism directly but reduce its reproductive success or promote tumors—even interfere with the process of copying the genetic code. "There is some evidence that PAH can affect methylation patterns," Griffitt says. "You stick a methyl group on DNA somewhere and then effect gene transcription. It's theoretically heritable."
Further, it is difficult to tell whether a decline in reproduction or an increase in cancer is a direct result of the BP oil spill, a natural oil seep, some combination of causes or another cause entirely—in addition to being difficult to detect in the first place. "We are starting to see some tumors and lesions in fish exposed to Deepwater Horizon [spilled oil]," Chesney notes. In fact, fish caught in the Gulf, such as red snapper, are showing signs of weakened immune systems that have allowed opportunistic infections. The cause may or may not be BP's oil spill.