The present invention relates to the use of one or more compounds as a molluscicidal and/or mollusc-repellant agent, wherein the one or more compounds are terpenes or oxygenated derivatives thereof. The present invention also relates to a molluscicidal and/or mollusc-repellant agent comprising one or more of the compounds of the present invention. The present invention also relates to the use of one or more compounds as an anti-barnacle agent, wherein the one or more compounds are terpenes or oxygenated derivatives thereof. The present invention also relates to an anti-barnacle composition comprising the one or more compounds. The present invention also relates to the use of a plant extract as an anti-barnacle agent.