Dispersed Oil Effects on Tropical Nearshore Ecosystems

Tropical and subtropical critical habitats are generally more fragile and slower to recover than temperate ones in which the environmental standards and guidelines are made. Fisheries nurseries are found immediately adjacent to shore in seagrass in the tropics, unlike temperate zones where fisheries are most frequently offshore and much of the adult fish catch is in this coastal region (the exceptions are a few highly migrating fish such as tuna). Studies have dealt with oil effects on corals and mangroves; fewer have dealt with seagrass. Very few studies have looked at dispersed oil on any of these habitats. The single dispersant used for mangroves and corals and the primary dispersant in seagrass studies was Corexit 9527, which showed no mortality on subtropical and tropical habitat species between 1 to 50 ppm (1:20 dispersant-to-oil dilution) for short (4 to 6 h) time periods. Higher concentrations of dispersed oil tested on seagrasses showed ranked sensitivity. Other dispersants have only been tested on seagrasses. Ranked sensitivity from nontoxic to very toxic appeared as in animal testing. The time of exposure and concentration of dispersants are important to increasing toxicity effects. Four species of corals were tested to Corexit 9527 1 to 50 ppm. Little difference in response was yet apparent. For mangroves, only the Western Atlantic red mangrove has been reported for the single dispersant Corexit 9527. (This manuscript was prepared in June 1987 when some ongoing experimental mangrove data were not yet published.) The Indo-Pacific basin critical habitat species and Arabian Red Sea species need similar testing for “safe limits.” Field testing of various dispersants is necessary. Regulators and planners must stop using the generic “dispersants” in oil spill contingency planning and name a nontoxic substance tested in their ecosystems since some dispersants are toxic and others are not. We must establish a network to disseminate recent work.