As of June 2010, the Deepwater Horizon BP oil spill in the northern Gulf of Mexico continues to dump oil and dispersants into the sea, and the Gulf of Mexico Loop Current has picked up this oil and is transporting it south to the tropical/subtropical coastal ecosystems of south Florida. The Florida Coastal Everglades Long Term Ecological Research (FCE-LTER) program in south Florida includes open water, seagrass and mangrove habitats that could receive oil. Mangrove forests and seagrass beds, and the faunal communities they support, are exceedingly sensitive to damage from oil spills. Oil is directly toxic to marine plants, and mangroves are sensitive to smothering and death when oil slicks wash ashore. The food webs of these coastal communities are highly sensitive to toxic compounds in oil, and impacted seagrass animal communities can be altered for many years after a spill. Given the susceptibility of the ecosystems of the FCE to oil spills, significant oil reaching this well-studied system could drastically alter the distribution of the marine communities, the structure of the food web, and the cycling of organic matter for years or decades after the spill. In this project, the investigators will measure hydrocarbon concentrations and food web structure at sites that may be directly impacted by the oil spill before the oil reaches them, and assess how these factors change following the arrival of oil. The researchers will test the hypotheses that 1) oil pollution shortens food chain length in coastal ecosystems, and 2) food web structure will be differentially affected in seagrass beds, where the primary producers are less sensitive to hydrocarbon pollution, compared to mangrove forests where the primary producers are killed by oil.
The ecological disaster playing out in the Gulf of Mexico as a result of the Deepwater Horizon BP oil spill is underscoring the importance that a sustainable costal ecosystem has in supporting the social and economic integrity of the human population in the region. This work will improve future oil spill clean-up efforts by defining the effects of oil-derived compounds on the structure and function of the food webs that support the important economic and cultural infrastructure of the region. Further, the FCE is located within the boundaries of Everglades National Park, an important natural resource; this work will document the extent of impact on the greater Everglades ecosystem by the oil spill.
In anticipation of the arrival of oil from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, we characterized the structure of the food webs of seagrasses and mangroves alonfg the shore of Everglades National Park, in the domain of the Florida Coastal Everglades Long Term Ecological Research program. We had hypothesized that oil would profoundly change thnature of the food web by a) killing the plants in the mangrove food web, thereby shifting the base of the food chain, and b) leaving the plants unharmed in the seagrass food web, but severely altering the makeup of the animals that consume plants, thereby changing the structure, but not the base, of the food web. We used chemical markers of the origin of food to delineate these food webs. In pareticular, we used stable isotope analyses that fingerprint the base of the food webs, and we used fatty acids that indicate more directly what food sources individuals have consumed. As expected, the base of the food webs, as indicated by the stable isotope analyses, were dominated by mangrove-derived carbon in the mangroves and seagrass-derived carbon in the seagrasses. However, the fatty acid tracers suggested that in both food webs, bacteria were critical in converting the seagrass and mangrove material into nutritious detritus before it enterred the food chains. We found no evidence that DWH oil reached our study area; hence there was no impact of the oil spill on the food web structure of our study sites.
