Below the Surface: Deep-sea Impacts of the BP Oil Disaster

May 2, 2011

Dr. Dan Thornhill takes a plunge into Gulf waters via the Johnson Sea Link II submarine

When Defender’s marine scientist, Dr. Dan Thornhill, and his colleagues at Auburn University began a three-year study on deep-sea animals in the Gulf of Mexico, they had no idea their research would focus on the impacts from the largest oil spill in U.S. history. It was a rare stroke of luck that in the year before disaster struck, the team had collected data from some of the places that would be most affected by oil. Now, he and his team of researchers are working to process data gathered a mile below the surface before, during and after the spill to see how the exposure to massive amounts of oil and chemical dispersants has impacted animals and ecosystems far below the water’s surface.

The Project

Dan and his colleagues were in pursuit of siboglinid annelids – animals as bizarre as their name would suggest. A group of tube worms found throughout the deep sea, siboglinids do not have a mouth or gut to digest food – in fact they don’t eat at all. Instead, these worms house dense colonies of bacteria within their bodies. The bacteria convert energy from toxic sulfides into sugar, feeding their worm hosts in the process.

Siboglinids (tubeworms) pre-oil disaster

Siboglinids are found in some truly unique and extreme ecosystems, oftentimes a mile or more below the ocean surface. These animals are found at hydrothermal vents, where the heat of the earth reaches the sea floor, and on the skeletons of dead whales scattered throughout the world. In the Gulf of Mexico, siboglinids live at methane seeps – areas where fossil fuels slowly and naturally bubble up through the sediments. As the fossil fuels move through the sediment, microbes change the chemicals into forms useable by these tube worms. The worms and their bacteria actually live off of the by-products of fossil fuels!

The goal of the research was to understand the relationship between siboglinids and their bacteria as well as how deep-sea animals flourish under such extreme conditions. In October of 2009, they surveyed the sea floor in the Gulf of Mexico using the submarine the Johnson Sea Link II. Using molecular genetic tools, the team collected samples and examined the unique species. Unseen to most, the deep-sea ecosystems at the bottom of the Gulf are beautiful and fascinating places, rich in biodiversity. In addition to the tube worms, the team found sea fans, crabs, lobsters, dense banks of hard corals, mollusks, brittle starfish and more.

Before the oil spill, deep-sea life was rich and vibrant

After the Spill

When the BP oil disaster began in April 2010, what had started as a basic research project rapidly morphed into a damage assessment. Many of the same locations that Dan and his colleagues visited the previous year were hit by the underwater plume of oil and dispersants from the spill. Although siboglinids live off of the byproducts of fossil fuels, they do not directly interact with oil under normal conditions. It was unknown how methane seep animals might fare in the face of this unprecedented catastrophe.

The team returned to the Gulf during and after the spill to take stock of the impacts of the spill. What they found was devastating – dead, dying, or injured animals covered in an oily brown substance. It was clear these animals were not equipped for such toxic exposure.

Oil-coated deep-sea animals post-disaster. Photo courtesy of Charles Fisher, PSU

Today, the team is trying to determine the extent of what’s been lost and how the surviving animals have responded to the disaster. This work will give us an idea of how these important, but little-known deep-sea ecosystems have coped with the largest oil spill in U.S. history. The outlook is bleak, but only by knowing more can we truly understand how oil disasters impact life far below the waves – and the risks we take when we drill in our waters.