“A deathtrap of mucus gashing through the water like flypaper.” That’s how Samantha Joye, a professor of marine sciences at the University of Georgia, describes the effect of the oil and gas from last summer’s disaster on the delicate marine organisms that inhabit the depths of the Gulf of Mexico.
When BP’s Deepwater Horizon offshore drilling rig exploded on April 20, 2010, Joye’s research team was among the earliest on the scene and the first to report huge underwater plumes of hydrocarbons gushing from the blown out Macondo well some 5,000 feet under water. Since May of last year, her team – which had been investigating microbial activity near the well before the blowout – has undertaken several research expeditions to the Gulf to observe conditions in deep water and on the sea floor. They are trying to understand the fate of this oil and gas, and how it has impacted the marine organisms that most of us never see.
Many of the memorable – and horrible – images from the BP blowout involved animals that live near the water’s surface: pelicans and baby sea turtles covered in oil, dead dolphins washed on shore, whole oyster farms destroyed. But to assess the long-term effects of the spill on the Gulf ecosystem, Joye and other scientists are focusing their investigations on creatures at the base of the marine food web: microbes, phyto- and zooplankton, and jellyfish-like organisms that live in the water column, and sea floor invertebrates. All play important and interdependent roles in the marine environment. How those creatures respond to the onslaught of hydrocarbons will be key to the future health of the Gulf of Mexico and its many inhabitants.
After the Macondo well exploded, oil gushed into the ocean for nearly three months. By the time the well was capped on July 15, nearly 210 million gallons (some 5 million barrels) of oil had been released. The oil spread over a vast area of the Gulf’s surface and washed ashore along more than 350 miles of coastline, oiling the shoreline from Louisiana to Florida. It coated birds, sea turtles, and marine animals, and made fishing and shellfish harvesting along much of the Gulf Coast impossible for most of the summer.
To keep the oil from having an even heavier impact on sensitive Gulf Coast marshes, wetland vegetation, and beaches, about 2 million gallons of chemical dispersants were applied to break up the oil at sea, both on the surface and at the deepwater well-head. More than 400 controlled burns of approximately 1.1 million gallons of surface oil were conducted offshore in the areas of heaviest oiling, while nearly 35 million gallons of oil and water were skimmed from the water’s surface.
How did the BP blowout affect the tiny creatures at the bottom of the marine food web, and what does it mean for the Gulf’s future health?
According to the “oil budget” released by the National Oceanic and Atmospheric Administration (NOAA), these cleanup and mitigation efforts removed nearly 75 percent of the oil released by the well. NOAA estimates the remaining oil is either just below or on the surface as residue; is washing ashore as tar balls; or is buried in sand. But less oil visible on the water surface doesn’t mean that oil has entirely disappeared from the water column. And, as Joye points out, NOAA’s oil budget does not include the significant quantities of gas (largely methane) released along with the oil. She says that while NOAA’s figures assume that the controlled burns completely removed the oil set on fire, her research shows that ash and some hydrocarbons ended up on the sea floor. Both have biological impacts. The lingering subsurface oil and gas are playing a key role in determining how the Gulf ecosystem and its sea life – from the large and charismatic to the obscure and microscopic – will recover from this trauma.
What Joye has witnessed on the sea floor is not pretty.
“The soft corals that should have been orange were white,” she said, speaking about what she saw on a dive in December. “There were oiled and dead brittle stars. Worms that should have been tightly coiled were lethargic and behaviorally impaired.” Joye’s team used photographic techniques to distinguish the Macondo oil from any from natural seeps and, she said, they found “blobs of oil all over the sea floor.”
Terry Hazen, senior scientist in the Earth Sciences Division at Lawrence Berkeley National Laboratory, whose work focuses on Gulf microbe communities that eat oil and gas and their response to the Macondo hydrocarbons, presents a less gloomy picture. He says that while there’s some oil in seabed sediment (partly from the failed “top kill” attempt when BP tried to plug the well by injecting drilling mud), “the good news is that much of the oil went away really fast,” devoured by microbes. Hazen’s research into which microbes degrade oil from natural seeps and which eat oil released from drilled wells will yield information about ways to clean up oil and other hydrocarbons. It will also shed light on how the presence of certain microbes affects the flow of nutrients in the Gulf.
Ben Van Mooy, a bio-geochemist at the Woods Hole Oceanographic Institution, explains that “oil contains a fantastic number of molecules.” Some of these are more appealing to microbes than others and some of that appeal is determined by the molecules’ structure. Hydrocarbon molecules that exist in “strings not rings,” he explains, are typically the ones that get eaten the most quickly. So microbes tend to eat the less toxic molecules more readily and “leave behind things that are more toxic” like benzene and other aromatic hydrocarbons with ring structures. What this means for the food web is that aromatic hydrocarbons – which pose various health hazards to living cells – may be left behind in the Gulf.
“What concerns me,” said Kim Warner, senior marine scientist with the nonprofit organization Oceana, is the fate of “all the chewed up carbon” – what’s left over after the microbes finish eating, and how that will affect the bottom feeders. As long as there is an extraordinary amount of oil in the environment, there will continue to be what she calls “blooms” of microbes that come to feed on the oil. Their presence as a food source and their leftovers, physical and chemical, will affect the fate of the rest of the benthic (or sea floor) environment. “We don’t know the toxicity of the leftover elements on the sea floor or how this will affect recruitment [biologists’ term for population growth] and what will make that environment hospitable again,” she said.
NOAA is conducting a series of surveys of the benthic environment, looking at hard surfaces and corals as well as the soft muddy bottom. But because this research will inform the Natural Resources Damage Assessment – part of the US government’s lawsuit against BP – no further details could be made available, said National Ocean Service spokesperson Ben Sherman.
Moving farther up the water column and the marine food web are the jellyfish and sea cucumber-like creatures known as pyrosomes or tunicates, great numbers of which were reported dead near the Deepwater Horizon wellhead last summer. “Pyrosomes usually occur in the upper water column [within a few hundred meters of the surface], so many have been exposed to hydrocarbons. And, they may have been exposed to the gas plumes and dispersants,” said Thomas Shirley, professor of biodiversity and conservation science at Texas A&M University.
“Pyrosomes probably have an important linkage in pelagic food webs, in that the pyrosomes consume a smaller size class of plankton,” he explained. “Pyrosomes are in turn consumed by a variety of predators, from ocean sunfish to turtles, tunas, and the juveniles of lots of fish species.” Just as in the Gulf’s benthic realm, it’s far too early to say what the long-term impacts of the “massive mortality” of pyrosomes may mean. But Shirley thinks it could prove an important piece of the puzzle.
Ultimately, what happens at the bottom of the food web affects those at the top. “Phyto- and zooplankton, shrimp, they have short life histories and reproduce in large numbers,” said Jackie Savitz, senior scientist at Oceana. “Larger animals with long life histories that reproduce in smaller numbers, like sea turtles, will have a more difficult time bouncing back. What happens when a baby sea turtle can’t find food?”
While different scientists have reached varying conclusions about how much oil, gas, and related compounds have ended up on the ocean floor, how much remains in the water column, and how thoroughly microbes have degraded the Macondo hydrocarbons, all agree that it is far too soon to know how the unnatural presence of so much oil and gas in the Gulf will ultimately affect its ecosystem.
“We’re in unknown territory here. It will take us a long time to sort things out and know what the true answers are,” Joye said.
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