MOBILE, Alabama – Much of the oil from the Deepwater Horizon oil spill never made it to the surface of the Gulf, instead becoming suspended in the water column, suggests research presented at a scientific conference held in Mobile.
Strange orange blobs, possibly oil or dispersant, continued to be found beneath the shells of larval blue crabs 4 months after the oil quit flowing. And Louisiana has lost large swaths of marsh to oil exposure, according to presentations at the conference.
The 40th annual Benthic Ecology Meeting was held at the Renaissance Riverview Plaza this week, drawing about 600 scientists from around the nation who study the creatures that live along the seafloor. The meeting was sponsored by the Dauphin Island Sea Lab and the University of South Alabama.
One of the emerging themes among scientists presenting their spill research was that many sea creatures appeared to be doing better than expected.
“We did not see a mass mortality event for crabs. Recruitment was a little lower than normal, but not a great deal lower,” said Erin Gray, a Tulane scientist who presented research on crab spawning during the spill.
Gray said female crabs, their eggs, and the newly hatched larvae were all clearly exposed to oil in Louisiana, Mississippi and Alabama. But years’ worth of data suggests an average crop of babies made it into marshes and estuaries, from Dauphin Island to south Louisiana.
Gray said the spill coincided with the peak spawning season. She and other scientists remain troubled by the large numbers of crabs that were found to contain the strange orange deposits beneath their shells. Crabs with the drops were found as far from the wellhead as Galveston, Texas.
Scientists have yet to figure out what the material is, with tests to identify dispersants or BP’s crude still pending.
“Over time, the droplets move into their eyes,” Gray said, discussing the crab larvae. “We’re seeing really high proportions of larvae with the orange drops … this is highly unusual.”
What happened to the oil? Large plumes sank, panels say
Two different groups presented research that examined the fate of oil in the Gulf, with both concluding that large plumes of oil sank to the depths of the sea.
“We can see it. There was a really large plume that stayed mostly in the deepest areas,” said Paul Montagna, a Texas A&M scientist who has studied contamination around oil platforms for decades. His presentation focused on research cruises conducted last fall after the well was capped. The goal was to map pollution along the seafloor.
He said that a typical platform has a contaminated zone around it a few hundred feet wide. The BP spill instead has a contaminated area that reaches 50 miles from the wellhead.
Montagna said it was likely that any oil on the seafloor would dissipate, leaving behind more persistent pollutants, such as heavy metals including mercury. He said the contamination was almost exclusively in the deepest areas beyond the continental shelf. The group did not find significant pollution in the Desoto Canyon, a deep area due south of Pensacola.
Young of many Gulf fish not dramatically affected
Research conducted out of the Dauphin Island Sea Lab suggests that the young of many fish species — some snapper, speckled trout and others — were not dramatically affected by the spill.
“If anything, 2010 showed up as a really good year for (mangrove) snapper. We thought they might be a poster child for fish affected by the spill,” because their larvae were drifting at the surface during the spill, said Ken Heck, a Sea Lab scientist. “The cessation of fishing during the spill, we essentially had a marine protected area out there.”
Heck said that some species that lay their eggs on the seafloor, such as triggerfish, might be affected more than animals whose eggs drift on currents. And he said there remained the potential for chronic problems that will only become visible with time.
“A large portion of the oil is still in suspension in the deep waters of the Gulf,” said Erica Staaterman of the University of Miami. “We had a sort of accidental experiment on our hands.”
Staaterman’s research — which included computer models of how the oil behaved underwater — suggests that nearly a million gallons of dispersants applied at the wellhead may not have played much of a role in causing the oil to sink.
“The temperature and pressure naturally created small particles of oil,” Staaterman said. Those drops became neutrally buoyant in the deep water and “never made it up over the edge of the continental shelf. Instead, it is just swaying in the current at depth.”
