Distribution of n-alkanes in marine samples from southeast Florida

Several authors have called attention to pollution and the insidious deterioration of nearshore waters and associated marine habitats of the Florida Keys. Some of the recognized and potential sources of pollution that have been reported are sewage effluents (Bright et al., 1981; LaPointe & O'Connell, 1988), marinas (Heatwole, 1987), surface water run-off from urban areas in the Keys (Heatwole, 1987) and the southeast Florida mainland (Jaap, 1984), wastes from fish processing facilities (Heatwole, 1987), and shipping wastes and oil spills (Jaap, 1975, 1984; Romero et al., 1981; Zheng & Van Vleet, 1988). Although any of these sources could be a causal factor of pollution in a regional context, only nutrient enrichment from sewage run-off has thus far been implicated as a significant and relatively widespread problem (LaPointe & O'Connell, 1988), albeit only in the shallow nearshore waters of the Keys. As part of a larger study to determine the principal source(s) and ecological consequences of pollution, samples of marine vertebrates (snappers and groupers), invertebrates (decapod crustaceans, scleractinian corals and molluscs), and sediments were collected at various times and locations and analysed for the n-alkane aliphatic hydrocarbons C-12 to C-30, and the isoprenoids pristane and phytane. Whereas the straightchain hydrocarbons are commonly present in both biological materials and petroleum, specific carbon suites and indices of n-alkanes have been used in pollution studies to help distinguish between biogenic and petrogenic sources (Lamparczyk et al., 1988; Pelletier et al., 1991). For example, odd number carbon chains tend to dominate in biological materials, whereas petrogenic (fossil carbon) materials have a high preponderance of even numbered carbons. The Caribbean corals, however, have been shown not to exhibit a strong odd or even carbon preference (Meyers, 1977). Sediment and tissue samples were collected during 10 trips to the Florida Keys from 1990 to 1992. Sampling locations, and regions corresponding to post hoc data pooling for sediment, are shown in Fig. 1. Briefly, the Florida Keys were divided into five regions: bay, nearshore Atlantic, Hawk Channel, reef track and ABC channels. Approximately the top 4 cm of sediments were collected from each site by a diver using pre-cleaned glass jars (I-Chem TM Research, Hayward, California) as scoops. To prevent contamination, jars were opened