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Oiled seabirds and turtles may have been the dominant images of the Deepwater Horizon oil spill, but new research shows that there was also massive harm to the microscopic creatures in coastal sands, lasting months after beaches were clean to human eyes. The research will be published June 6 in the journal Public Library of Science (PLoS) ONE.

Before the oil hit the coast, the beach sand around Dauphin Island, Ala., teemed with a diverse mix of microscopic organisms such as worms, fungi, protists, algae, and larval stages of larger species, said Holly Bik, a postdoctoral researcher at the University of California, Davis Genome Center and first author on the paper.

Four months later, the beach population was starkly different, largely dominated by just a few species of fungi and a few species of nematode worms.

"It went from a very diverse mix of species to being dominated by a few predators and opportunists," said Bik, who carried out the work as a researcher at the University of New Hampshire.

Within days of the April 20 blowout, but before oil reached the coast, researchers from Auburn University, Ala. lead by Professor Kenneth Halanych collected samples from the beaches to establish a baseline. Bik, Professor W. Kelley Thomas at the University of New Hampshire and Jyotsna Sharma, assistant professor at the University of Texas San Antonio, returned to collect a second set of samples in September the same year, after the beaches had been oiled and then cleaned.

The team surveyed species less than a millimeter in size, including nematode worms, fungi, single-celled protists, and algae living in the sand. The researchers used high-throughput genomic methods, extracting DNA and sequencing millions of genetic “barcodes” (18S ribosomal RNA genes) to characterize the biological assemblages inhabiting Gulf coast beaches.

"The development of these genomic tools provides a detailed understanding of the biological consequences of such environmental disasters and is the first step toward mindful approaches for mitigation and remediation of this oil spill and those we will face in the future,” Thomas said.

In addition, Sharma carried out an analysis of nematode worms, identifying these animals by eye under a microscope.

The deceptively clean appearance of the beaches in September contrasted with the biological changes below the sand, Bik said.

"What struck me was that you wouldn't have known there was an oil spill — most of our sample sites looked like normal beaches. But when we analyzed the genomic data, there seemed to be all these biological repercussions going on," Bik said.

Microbial organisms are at the "base of the pyramid" that keeps the ecosystem healthy, providing food and nutrients for other animals, Bik said. Tiny nematode worms churn up sediments and contribute to the cycling of carbon, nitrogen, and sulfur within marine ecosystems.

"They're the machinery that keeps the ecosystem working," she said.

The researchers do not yet know how long the impacts of the oil spill will last, whether the microscopic beach life will return to baseline, or if sediments will be repopulated with a new set of organisms. The team has continued to collect samples at the same sites. Those results are still being analyzed.