June 7, 2012
Deepwater Horizon Spill Affected Microbial Communities
Brett Smith for redOrbit.com
While the tar-stained beaches from the 2010 Deepwater Horizon oil spill may be long gone, the Gulf of Mexico´s smallest residents are still reacting to its effects.
Samples collected around Dauphin Island, Ala., and Grand Isle, La., just before oil reached the shore and again several months later showed major discrepancies in the distribution of microscopic marine life populations including those of metazoan phyla, protists, algae and fungi.
"It went from a very diverse mix of species to being dominated by a few predators and opportunists," said lead author Holly Bik, a postdoctoral researcher from the University of New Hampshire.
Using two parallel methodologies, the team examined species less than a millimeter in size, including nematode worms, fungi, single-celled protists, and algae living in an along the island beaches. The researchers sequenced millions of RNA genes to characterize the biological genotypes inhabiting Gulf coast shorelines at the times the samples were taken. They also used microscopes to do a taxonomic analysis of nematode worms.
Bik and senior author W. Kelley Thomas, director of the Hubbard Center for Genome Studies, found that the communities of microbial eukaryotes in the sediments shifted dramatically from highly varied communities to an almost exclusively fungal community. In examining the nematodes, researchers discovered that the post-spill samples were dominated by more predatory and scavenger nematodes.
"The fungal taxa that were there were previously associated with hydrocarbons," Bik added, citing the post-spill fungi sampled from the Grand Isle sites that are suspected to utilize hydrocarbons and thrive in oil-polluted conditions, which are less hospitable for other species.
The proliferation of these hydrocarbon-loving microorganisms is both a blessing and a curse. Many experts were predicting the large role they would play in cleaning up and breaking down the oil spill. In fact, this principle is employed by oil companies in Nigeria to remediate oil polluted sites in a process known as Remediation by Enhanced Natural Attenuation (RENA). The microbial degradative mechanisms appear to be the natural processes that eliminate the bulk of oil pollutants after an initial physical and chemical breakdown has occurred.
However, the massive proliferation of these species is bound to have an impact all the way up the food web.
"Long-term impacts might not be so worrisome if microbial eukaryotes are able to recover quickly, but if the beaches remain depauperate -- fungal-dominated -- or a different community assemblage takes over following the oil spill, we may see long-term repercussions in Gulf ecosystems [that] impact the food chain, or nutrient cycling," Bik told Wired UK.
"If you turned up at the beach in September and looked around, you would have had no idea there was an oil spill. Yet our data suggest considerable hidden initial impacts across shallow Gulf sediments that may be ongoing."
The report noted that ongoing research and sampling should aim to determine whether fungi are thriving and persisting long-term and whether the shift in communities is a temporary phenomenon.
Image 2 (below): Belleair Boulevard on Dauphin Island, Ala., in September 2010. Credit: Holly Bik