Effects of oil and dispersant on phytoplankton communities in northern Gulf of Mexico estuaries

On April 22, 2010 the offshore drilling unit Deepwater Horizon sank in the northern Gulf of Mexico, releasing an estimated 780,000 cubic meters of Sweet Louisiana Crude and 205,000 metric tons of methane. In light of the Deepwater Horizon oil spill, it is important to understand how oil and its constituents can affect the phytoplankton communities in the Gulf of Mexico because phytoplankton are the base of classical food webs. The affect of oil and dispersant on natural assemblages from several Gulf of Mexico estuaries was determined at the community level in enclosed microcosm experiments. Natural phytoplankton assemblages from Apalachicola Bay, Pensacola Bay, Pensacola Beach, and Bay Jimmy were treated with water accommodated fractions of oil, dispersant, and dispersed oil for seven days. Samples taken throughout the incubation were analyzed for photosynthetic efficiency, chlorophyll a concentration, and community structure. Dispersed oil had the largest effect, though not always negative, and effect on cell functions is magnified by exposure to ultraviolet radiation. Hydrocarbons are not always toxic to phytoplankton in Gulf of Mexico estuaries.