Oil gushed into the Gulf of Mexico from a hole in the depths of the ocean for 86 days after the Deepwater Horizon explosion, resulting in one of the largest maritime oil spills in history. Since the wellhead was capped in July, the surface oil has seemingly disappeared, there are no new images of oiled birds or massive surface slicks visible from space, some fisheries have reopened, and the previously intense media coverage has shifted to the economy and the upcoming election.
Many are left with the impression that the BP spill event is over, and it is time to move on. However, many environmental scientists expect that the effects of this oil spill are only now becoming evident and that they may persist for many years. As scientists continue their efforts to study the ecological effects of this massive disaster, they seek to dispel some myths that are gaining traction with the public.
At a recent workshop sponsored by the National Science Foundation, participating researchers identified some common myths that are emerging and felt compelled to provide scientific perspectives on these issues for the benefit of the public and decisionmakers. The main message is this: It is likely that we have not yet seen the most significant impacts for marine and coastal organisms and humans. Oil spills will continue to occur in the Gulf of Mexico and elsewhere, and we have to learn our lessons from this disaster to plan for the future.
Myth 1: Now that the well is capped, we no longer need to worry about oil on our shores.
Since no new oil is entering the gulf from the blown-out wellhead and the surface oil has largely disappeared, many are tempted to think that coastal ecosystems are no longer in danger. The reality is that much oil persists in the environment, within or close to sensitive coastal and deep water habitats, and this oil could be the source of long-term, persistent, low-level exposures to coastal life.
We have learned from previous oil spills, such as the Exxon Valdez in Prudhoe Bay, that toxic oil can persist in the environment for decades. We now know that a significant amount of oil from the BP spill persists in deeper waters of the gulf and in thick layers covering large areas of the sea floor. Though an impressive effort has been made to clear beaches of surface oil, it has seeped into the sand and sediment and remains hidden below the surface of beaches and marshes. Storms are likely to resurrect the oil that is currently hidden from sight, and re-expose beaches and other sensitive coastal habitats. Such long-term periodic oiling will have persistent toxic effects on resident wildlife as it has in Prudhoe Bay. Ecosystem recovery from oil spills is often delayed because species within communities have complex interactions, and effects on one species can impact other species in ways that are difficult to predict.
Myth 2: Dead animals reflect the most significant negative impacts from oil contamination.
Most people are deeply disturbed by images of oiled birds, turtles and dolphins that are struggling to survive the immediate crisis of oil exposure. However, scientists have learned a surprising but important lesson from other oil spills such as the Exxon Valdez: It is the non-lethal effects on wildlife that are most important for the long-term integrity of populations. Examples of such nonlethal effects include tissue damage that affects organ function, damage to the DNA that makes up the genetic code, disruption of hormone functions, or decreased growth or hatching success of embryos. These effects are much more likely than outright mortality to influence the severity of population decline and the rate of recovery for organisms such as fish, shrimp and birds. Scientists are poised to study these critically important effects, but such research efforts will need to be sustained over a longer time than it takes to document mortality alone.
Myth 3: Attributing changes in the environment to the oil should be easy.
It is tempting to conclude that the absence of fish or shrimp from a region implies an oil effect. Or similarly, that the abundant presence of animals implies lack of oil impact. As many fishermen know, however, coastal ecosystems are highly variable in space and time. That is, animals move around and their numbers change depending on many variables such as tidal cycle, season, ocean currents and food availability. Accordingly, it is hard to define what is "normal" for population densities at a particular place and time. We can only attribute ecological effects of the oil spill through carefully designed scientific studies. This careful design must include a sufficiently large geographic area to allow comparisons among multiple sites over time, especially considering that the effects might be patchy. This comparison also requires data from before the oil spill, and from multiple locations that differ in severity of oil exposure, in order to capture natural variability and detect unexpected changes that coincide with oil exposure.
Myth 4: Since scientists have learned much from studying other oil spills, nothing new is to be learned from studying the BP spill.
All oil spills share some common risks and effects, and we have gained some broadly applicable lessons from past spills that are being used to inform studies of the BP spill. But the chemical nature of crude oils varies and each ecosystem is different. As a result, major oil spills require individually tailored research programs to document and learn about their effects. The BP spill, especially, has many unique attributes that pose new scientific questions. For example, the volume of oil spilled, the volume of dispersant applied and the depth at which this all unfolded is unprecedented, and collectively these characteristics affect how the oil is distributed in the ecosystem. The Gulf of Mexico also harbors many sensitive and complex ecosystems that will respond in unique ways to oil, including sea grass beds, mangrove forests, sub-tropical coral reefs, sandy beaches and salt marshes. Finally, the frequent hurricane events in the gulf may complicate the predicted dispersal and effects of spilled oil.
Myth 5: All oil cleanup activities are beneficial.
When faced with looming impacts from the BP spill, people rapidly mobilized and proposed diverse plans to keep the oil from coming ashore. These strategies ranged from standard responses such as booming, skimming and burning, to more inventive plans like dumping large quantities of human hair to mop up the oil, building massive offshore sand barriers, and opening the floodgates on the Mississippi River to push back advancing oil. It should be recognized that some well-intentioned interventions can have serious unintended consequences; these should be considered together with the risks of oiling. Occasionally, unusual oil spill responses are justified if they do some damage but have the overall effect of mitigating the risks of contamination to sensitive habitats. These interventions are not justified, however, when they are ineffective and cause more harm than good. For example, a freshwater pulse from the Mississippi River was intended to drive back the advance of oil by flooding coastal marshes, but it appears that this freshwater input was responsible for extensive oyster kills. Accumulating information on the effectiveness of different cleanup activities and associated consequences in response to the BP spill will be beneficial when considering responses to future spills. We need to be strategic about how we intervene, and not blindly adhere to the mantra that "doing something is better than doing nothing."
The well has been plugged, and for that we are all breathing a sigh of relief. People whose livelihoods depend on a healthy Gulf of Mexico are starting to repair, rebuild and recover. We all sense the value of this ecosystem, either because of its economic importance or because of its intrinsic value as a globally recognized hot spot of biodiversity and beauty. Though clearly visible oiling and tragic images of dead, oiled animals have passed, sensitive habitats are still at risk from insidious long-term exposures to lurking oil, and these exposures are likely to have the greatest consequences for population decline and the pace of recovery. This disaster demands our continued attention and careful research.
Andrew Whitehead is an assistant professor in the Department of Biological Sciences at Louisiana State University and lead author of this article prepared by 26 ecologists from the Gulf Coast Ecology Working Group as a result of a workshop funded by the National Science Foundation on impacts of the Deepwater Horizon oil spill. University of South Florida professor and chair of the Department of Integrative Biology, Susan Bell, and assistant professor Christina Richards are members of the group. The opinions and conclusions do not necessarily reflect the views of NSF.