Scientists Look to Food Webs for Better Understanding of Oil Spill Effects

By Matt Phillips, Outreach Coordinator, National Wildlife Federation

When trying to understand how ecosystems function, scientists often look at food webs–the complex relationships between animals, insects, plants, and bacteria that govern who eats whom.

Food webs in the Gulf of Mexico are as complex as they come. The different habitat types, from forests to wetlands to ocean, mean a diverse array of species. The Gulf food web would be nearly impossible to understand in its entirety, but we can simplify it into a chain to help us think about it. Plants form the base of this chain, as they convert sunlight into the energy that fuels the entire system. Plants are eaten by herbivores, who are then eaten by larger organisms. Scientists can learn a lot about how an ecosystem functions by studying the ends of the chain–the plants at the bottom and the animals that occupy the top. However, it’s the species in the middle that provide crucial linkages.

They measured the density of arthropod populations in patches of Spartina alterniflora, a grass that dominates Gulf coast marshes, while oil was washing up on marsh shoreline in 2010 and again one year later. For comparison, they visited 12 marshes with oil and 10 with no oil. They ensured the vegetation and soil were similar in each location to negate any differences between habitat types.

Their results were both striking and hopeful. During 2010, they found half as many arthropods in the marshes that had oil as in those with no oil. Because birds, fish, and even plants depend on these organisms, losing half the population could potentially devastate the ecosystem. But by 2011 arthropods in the oiled marshes were back at the same densities as in the unoiled marshes. It seemed that arthropods were primarily susceptible to the direct effects of oil. Oil may remain in wetlands for decades after a spill, but it usually seeps into the soils under the marsh grass. The arthropods in this study lived in the grasses above the marsh surface. Once the oil disappeared into the soil, their populations returned to normal.

This study presents a more important conclusion than simply the resilience of arthropods to oil. Ecosystems are intricate webs of interactions between the living and non-living environment, and looking at one organism, relationship, or phenomenon may not reveal any significant truth about the ecosystem as a whole. Except for a thin sheen of oil, the marshes in this study appeared healthy. But, in fact, oil had wiped out half the arthropods. We should treat ecosystems as the fragile, profoundly complex systems they are. Protecting them should be the top priority. Any disturbance can have widespread and unpredictable consequences.

To learn more about our coalition and the plans to restore our marshes and wetlands, click here.  More information about the ongoing effects of the BP oil spill can be found here:  "Understanding effects of chemical dispersants on marine wildlife is critical to whale population" and  "Five years later, scientists gather to assess ongoing impact of BP oil spill."