Antifouling activities of anti-histamine compounds against the barnacle Amphibalanus (=Â Balanus) amphitrite

The barnacle Amphibalanus (= Balanus) amphitrite is a typical marine fouling invertebrate, with adults releasing planktonic larvae that settle and further metamorphose into juveniles on submerged surfaces. The mechanisms regulating larval selection for settlement surface and metamorphosis initiation have been proposed to have a close relationship to neurotransmitters. In this study, a total of 35 signal-influencing pharmaceutical compounds affecting several neurotransmitters were examined in an antifouling bioassay using cyprid larvae of A. amphitrite to search for new antifouling compounds. The results indicated that 18 of the 35 compounds were effective against the larval settlement and metamorphosis of the barnacle A. amphitrite, with nontoxic effects at concentrations of 20 μg mL− 1. By reducing the treatment concentrations, a 5-HT3 receptor antagonist of Ondansetron; two epinephrine β2 receptor agonists of Propranolol and Clorprenaline; and five histamine H1 receptor antagonists, including Loratadine, Antazoline, Clemastine, Azelastine, and Triprolidine were found to be very active against the larval settlement and metamorphosis of A. amphitrite, with EC50 values lower than 1.6 μg mL −1. In a recovery bioassay, the larvae treated with a histamine H1 receptor antagonist of Triprolidine regained the ability to settle and to metamorphose into juveniles in fresh artificial seawater. The settlement and metamorphosis of the recovered larvae were further enhanced by the addition of 5 × 10− 9 M histamine. The results of the present study indicated that some of the compounds influencing neurotransmitter signaling, especially histamine H1 receptor antagonists, are promising new antifouling candidates.