Effects of the fish anesthetic, clove oil (eugenol), on coral health and growth

Ecological research within coral reefs often requires the use of anesthetics to immobilize organisms. It is therefore important to consider the effect of these chemicals on the surrounding flora and fauna, particularly to the corals themselves. We quantified the effects of clove oil, a commonly used fish anesthetic, on the growth and occurrence of bleaching in three species of corals: Acropora striata, Pocillopora verrucosa, and Porites australiensis. We compared coral responses to five treatments: a gradient of four clove oil concentrations (0-28%) in seawater, and one concentration of clove oil (14%) in ethanol. Each week, we assessed the presence of bleaching, and then applied the treatment. We measured growth over the duration of the 6-week experiment using the buoyant weight technique. Growth and bleaching showed a dose response to clove oil exposure, and the use of ethanol as a solvent had an additional deleterious effect, as also suggested by observed changes in concentrations of eugenol following field application. Overall, growth was reduced by 37.6% at the highest concentration (28% clove oil in seawater) relative to the control (0% clove oil). The reduction in growth was nearly as great (35.3% of the control) at half the concentration of clove oil (14%) when dissolved in ethanol. These results suggest the repeated use of clove oil (even without a solvent) can deleteriously affect corals.