Harmful effects of chronic oil pollution on a Red Sea scleractinian coral population

Field observations and histological studies on two populations of the coral Stylophora pistillata, in a chronically oil-polluted reef and a pollution-free control reef, at the northern Gulf of Eilat, Red Sea, revealed detrimental effects on different stages in the life history of this coral: the colony, gonads and planulae. The coral population at the oil-polluted reef showed significant differences (P < 0.05) in several aspects compared with the coral population at the control reef: Higher mortality rate of colonies, smaller number of breeding colonies, a decrease in the number of ovaria per polyp, a decreas'e in the average reproduction index, smaller number of planulae produced per coral head (fecundity was four times higher in the control reef), lower settlement rate on artificial objects in the field, and in the laboratory -lower settlement rate of planulae on petri-plates with increasing concentrations of oil. The combination of a long-term study, field observations on individually tagged corals, laboratory experiments and field work and broad knowledge of the ecology and biology of the species investigated, elucidated the present results, in contrast to many other field reports.