The Food Chain in the Gulf
Organisms in a food chain are grouped into trophic levels, based on how many links they are removed from the primary producers. Plants or phytoplankton are in the first trophic level; they are at the base of the food chain. Herbivores (primary consumers) are in the second level. Carnivores (secondary consumers) are in the third. Omnivores are found in the second and third levels. At the Dauphin Island Sea Lab in Alabama they decided to track a stable isotope of carbon from the BP oil spill and try and discover how quickly it was being incorporated into the food chain. Dr Monty Graham and his colleagues showed that as the oil approached northern Gulf coastal waters in pulses, there was a dramatic decrease in the carbon isotope weight signature over about a four week period. With all other possible sources of light carbon ruled out, they concluded that oil-carbon entered the plankton food web as micro-organisms fed upon the oil-consuming bacteria.
According to Graham, it has not been disputed whether the oil would be consumed by marine bacteria but there was a debate on what this would ultimately mean for the rest of the food web.
"We showed with little doubt that oil consumed by marine bacteria did reach the larger zooplankton that form the base of the food chain. These zooplankton are an incredibly important food-source for many species of fish, jellyfish and whales," says Graham.
In some cases a toxic material (call it Mercury as an example) will enter the food chain and gradually concentrate as it goes higher. The measured oil carbon is not necessarily toxic and may represent compounds that are being changed into other organic compounds.
Graham says that this doesn't necessarily mean that crude oil toxins were transferred into the zooplankton, but it does show a food web pathway by which other components of the oil could reach higher in the food web.
What is clear is the BP oil has entered the Gulf food chain faster than expected and was literally consumed. The end effects, if any, are not known.