Tropical Oil Pollution Investigations in Coastal Systems (Tropics): The Effects of Untreated and Chemically Dispersed Prudhoe Bay Crude Oil on Mangroves, Seagrasses, and Corals in Panama

A multidisciplinary long-term field experiment was conducted to evaluate the use of chemical dispersants as a means of reducing adverse environmental effects of oil spills in nearshore, tropical waters. Three study sites whose intertidal and subtidal components consisted of mangroves, seagrass beds, and coral reefs were studied in detail before, during, and after exposure to untreated crude oil or chemically dispersed oil. This study was intended to simulate an unusually high, worst-case exposure level of dispersed oil and a moderate exposure level of untreated oil. The third site served as an untreated reference site. Assessments were made of the distribution and extent of contamination by hydrocarbons over time, and the short- and long-term effects on survival, abundance, and growth of the dominant flora and fauna of each habitat. The whole, untreated oil had severe, long-term effects on survival of mangroves and associated fauna and relatively minor effects on seagrasses, corals, and associated organisms. Chemically dispersed oil caused declines in the abundance of corals, sea urchins, and other reef organisms; reduced coral growth rate in one species; and had minor or no effects on seagrasses and mangroves. Conclusions were drawn from these results with respect to decision making at the site of the actual spills based upon trade-offs on the consequences of dispersing or not dispersing the oil.