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Reflections from Marine Ecologist Thomas Shirley

Putting Perspective on the Deepwater Horizon Disaster

Deepwater Horizon on fire

U.S. Coast Guard

"Lessons gathered from long-term studies of the Exxon Valdez oil spill offer caution in believing that the effects of the Gulf of Mexico spill were minor and that the worst is behind us."

—Thomas Shirley

The BP Deepwater Horizon oil spill of 2010 was not a spill. A spill is knocking over a glass of water. This was an oil well blowout—an 87-day and 200-million-gallon environmental disaster that resulted in the deaths of 11 workers, interrupted the livelihoods of tens of thousands of people, spoiled a variety of marine habitats and caused the deaths of thousands of marine organisms.

This disaster was fundamentally different than prior oil accidents. These have been in shallow water or leaked at the surface; oil and gas gushed from the Deepwater Horizon wellhead at a depth of about 5,000 feet. The use of 1.8 million gallons of dispersant, much of it released at the wellhead at depth, heightened concerns and anxieties. Millions of viewers around the world continuously watched the oil and gas spewing out via underwater video cams mounted on remotely operated vehicles (ROVs) at a rate equivalent to two Exxon Valdez oil spill disasters weekly, not knowing how long the incessant gushing would continue. By the time the well was capped, the amount of oil lost to the sea was equivalent to the loss of approximately 19 Exxon Valdez oil tankers. And unlike the Exxon Valdez spill in which no dispersant was used nor oil burned, 1.8 million gallons of dispersant and 411 controlled burns were used in the Deepwater Horizon disaster.

Oiled pelican being washed
Many pelicans were among the Gulf of Mexico animals found covered in oil and so had to captured, cleaned and rehabilitated prior to being re-released in the region. Justin Stumberg, U.S. Navy
BP, the U.S. Coast Guard, federal and state agencies, universities, and nongovernment organizations mounted the largest oil spill response in U.S. history to cope with the disaster. Up to 6,800 vessels, 45,000 workers and more than a hundred airplanes toiled daily to try to find and contain the oil, save oiled animals, measure the early effects of the disaster, model its probable dispersion and cap the well. However, the same techniques that had been used 31 years earlier in the Ixtoc blowout in the shallow, Mexican waters of the southern Gulf of Mexico were tried again—and failed again. In the past three decades, no new technologies, structures or devices for controlling a blowout have been created. In retrospect, it is now obvious that once such a disaster happens at great depths, neither the oil industry nor government agencies have the capabilities of controlling the high pressures, quickly containing the oil, halting the blowout or dealing with the oiling of thousands of birds, marine organisms and sensitive habitats.

In addition, no new preventative measures for oil spills have been developed in this time frame either. The contingency plans that had been submitted and approved prior to the Gulf disaster appear to have been woefully inadequate; they primarily served the purpose of allowing exploration and drilling to proceed. Our legal system will determine if the fiscal and safety inadequacies used in the drilling of the Deepwater Horizon will warrant criminal culpability.

What is the fate and effects of the more than 200 million gallons of oil, 1.8 million gallons of dispersant and 500,000 tons of gaseous hydrocarbons (primarily methane and pentane) that were released into the Gulf? One well-regarded report the Congressional Research Service released last December stated that only 22 percent of the oil (44 million gallons) was unaccounted for. Only a relatively small number of seabirds (approximately 3,634), and much fewer numbers of sea turtle and marine mammal mortalities were attributed to the spill. Mortalities of fish, crabs, shrimp, jellyfish, sea cucumbers and a large diversity of other marine taxa had not been quantified.

John “Wes” Tunnell, associate director of the Harte Research Institute for Gulf of Mexico Studies and my colleague, submitted an expert opinion on January 31, 2011, to Kenneth Feinberg, the claims administrator for the Gulf Coast Claims Facility, which provides estimates of when the fisheries of the Gulf of Mexico will return to their prespill status. The conservatively worded report was prefaced with a statement that although true losses to the ecosystem may not be known for years or decades, the Gulf was recovering quickly, and fish, crab, shrimp and oyster takes were predicted to return to normal within a year or two, although oiled oyster reefs might require six to eight or even 10 years to recover. In summary, the effects of the largest oil spill in the history of the United States were considered surprisingly minor.

Oil in marsh
Oil infested the marshes along the coast of Louisiana. Eileen Romero

Can this be true? Indeed, the Gulf of Mexico is better adapted to oil than most marine habitats. According to a 2003 National Research Council report “Oil in the Sea III: Inputs, Fates, and Effects,” an average of about 50 million gallons of oil are lost into the Gulf annually from natural oil and gas seeps, and as a result, populations of oil-degrading microbes abound. Surface water temperatures and sunlight intensities are high, aiding in oil degradation. And, we had a remarkable string of luck: not a single hurricane or major tropical storm event entered the area of the oil during the entirety of cleanup and recovery efforts. Similarly, the Loop Current did not extend northward into the area of the oil (or only marginally) or carry the oil into the Strait of Florida or the Florida Keys.

However, lessons gathered from long-term studies of the Exxon Valdez oil spill offer caution in believing that the effects of the Gulf of Mexico spill were minor and that the worst is behind us. Less than 10 percent of tagged carcasses of oiled animals were ever recovered from experiments conducted in response to the Exxon Valdez oil spill. NOAA Fisheries Services estimated that the less than 11 million gallons of oil spilled into the surface waters of Prince William Sound killed more than 400,000 sea birds, 4,000 sea otters and many large marine mammals. Twenty-two years after that Good Friday disaster, numerous sea bird species and some sea otter populations and orca pods have not yet recovered, and one pod was doomed to extinction. The Prince William Sound Pacific herring populations collapsed four years after the spill, causing the commercial fishery for this species, which had exceeded 10,000 tons per year, to be closed.

The Exxon Valdez oil spill also taught us that sublethal and indirect effects, such as reduced growth and reproduction, can be much more damaging to wildlife populations than immediate, direct mortalities. We learned that long-lived species that are slow to reach maturity and have low reproductive rates are most vulnerable to oil effects. And we learned that excessive cleaning and bioremediation can be as harmful as oil.

We also learned that litigation may persist until long after most of the environmental damage is gone. Exxon has successfully appealed court decisions and reduced their awards to claimants to less than 10 percent of the original amount.

So what does this mean in relation to potential long-term effects of the Deepwater Horizon disaster in the Gulf of Mexico? Some of the region's high-profile marine animals are easy subjects of apprehension. Considered vulnerable are the more than 1,600 sperm whales that live in the northern Gulf and dive to feed on the deep-dwelling squids, fishes and crustaceans in those waters; they are long-lived, slow to reach reproductive maturity and have a few offspring. The dolphins and porpoises that live in the area of the disaster have similar life history traits. Likewise, the approximately 1,000 whale sharks, the largest fish in the sea, are a major concern; approximately 90 were observed in a single aerial photograph in waters close to the Deepwater Horizon disaster last summer. Hundreds of dead juveniles and adults of the five species of long-lived sea turtles inhabiting the Gulf were recorded in the months following the spill, but the fate of thousands of younger turtles remains unknown. The effects on bluefin tuna populations, whose only spawning ground is in the area of the western Atlantic overlapping the location of the spill, also are unknown. Another 1,270 fish species that are both commercially and ecologically important inhabit the waters around and above the wellhead.

Thomas Shirley and Slyvia Earle in ROVs prepare to explore the ocean's depths
Marine researchers Sylvia Earle (left) and Thomas Shirley prepare to dive in the Dual Deepworker submersibles to examine the effects of oil on deep benthic communities in the northern Gulf of Mexico in January 2011. Harriet Nash, Harte Research Institute

Yet most of the marine communities near the almost mile-deep Deepwater Horizon wellhead are “out of sight, out of mind” and exceedingly difficult to study. Even so, they could be among the most valuable and most vulnerable. Perhaps a cruel irony is that the area encompassing the wellhead has been found to contain more species than than any other comparable depth in the Gulf of Mexico—1,728 crabs, shrimps, clams, worms, sponges and other marine species. These deep fauna are vital links in food webs and healthy marine ecosystems. Some deep-water coral species in the oiled area, for example, that were recently discovered to be 2,200 years old serve as the condominiums of the deep, providing complex habitats for many other species. Others are important in sediment bioturbation activities and mineral reprocessing, which could have high economic and ecological value. Yet these deep benthic communities are likely to have been in the areas of highest concentrations of oil, gas, dispersants and drilling muds, and many of the animals are largely sedentary and cannot flee the effects of the toxins.

How long the organisms around the wellhead will take to recover is unknown. During the Exxon Valdez spill, the oil was at the surface and few effects to deep-water species were documented. With the Deepwater Horizon disaster, it is becoming increasingly obvious that much of the oil may have settled in broad areas surrounding the wellhead.

If we don’t study the Deepwater Horizon disaster, we will see no effects. This may be a preferred alternative for those in the oil industry who will be funding studies or facing legal liabilities. However, the effects of the disaster on the different species, their ecological values and their interactions will remain unknown. A wide-array of long-term studies should be undertaken. The research should encompass not only biological and toxicological studies but should also encompass physical and chemical oceanography, meteorological studies, environmental engineering studies, and sociological and socioeconomic studies of coastal communities. If this research is not conducted, we will not be prepared for the future disasters that will surely occur as we resume our search for energy in the deep waters of the Gulf of Mexico.


Thomas ShirleyThomas Shirley is the Endowed Chair for Biodiversity and Conservation Science and a professor at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi. Shirley has published articles about the ecology and physiology of marine mammals, sea birds, invertebrates as well as pollution biology and conservation issues. He has described new species of invertebrates from around the world, including the Antarctic, Arctic, Philippines, Mediterranean, Alaska and the Gulf of Mexico. Shirley’s recent research has addressed the ecology of commercially important crabs, distribution of invertebrates on WWII shipwrecks, seamount ecology, organisms associated with deep-sea corals, ecology and systematics of priapulid marine worms, and ecology of benthic invertebrates in fresh and marine waters. He has served as an advisor to many research, conservation and other organizations on the potential damage of the Deepwater Horizon oil disaster and how to address oil spills.