Photoinduced toxicity of the polycyclic aromatic hydrocarbon, fluoranthene, on the coral, Porites divaricata

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The synergistic effect of ultraviolet radiation (UVR) and a polycyclic aromatic hydrocarbon (PAH) was tested on the coral Porites divaricata. Small branches were incubated in different concentrations of fluoranthene followed by exposure to ecologically relevant levels of natural solar radiation, with and without UVR. Exposure to the highest concentration of fluoranthene (60 μ g L− 1) resulted in decreased photochemical efficiency of corals exposed concomitantly to UVR but not in corals exposed to 60 μ g L− 1 fluoranthene without UVR. After 6 days, most coral samples that were exposed to fluoranthene and UVR bleached or died (78%) on the upper side of the branches. At 60 μ g L− 1 fluoranthene with UVR, 11 out of 12 samples died and the remaining sample bleached, much greater than the number of samples that bleached in manipulation or solvent controls. On the under side of the same samples, where the coral polyps are naturally protected from UVR, 11 out of 12 samples remained healthy and intact. The high UVR doses that shallow water dwelling corals receive combined with the results of this study show that photoinduced toxicity of PAHs is a stress factor that needs to be studied in more detail in coral reef ecosystems.