Histamine promotes the larval metamorphic competence of barnacle Amphibalanus amphitrite

The larvae of the typical marine-fouling barnacle develop into competent stages to settle on submerged surfaces, metamorphose to juveniles, and finally grow into adults. In this study, the presence of histamine (a neurotransmitter molecule) in both nauplii and cyprids of the barnacle Amphibalanus amphitrite was verified by analysis with High Performance Liquid Chromatography with a fluorescence detector (HPLC-FL) after O-phthalaldehyde derivatization. To clarify the functions of histamine in the larvae, two bioassays were further performed, using the nauplii and cyprids, respectively. In the presence of 5 x 10(-9) M histamine, 80% of low-energy-containing cyprids settled and metamorphosed to juveniles after only 48 h of incubation, which was significantly higher than in the absence of additional histamine. Moreover, the presence of 5 x 10(-10) M histamine also significantly increased and accelerated the metamorphosis of nauplii to cyprids. An antihistamine compound of triprolidine hydrochloride completely inhibited cyprid settlement and metamorphosis at a concentration of 1.3 mu g ml(-1), which indicated that it possessed strong antifouling effects against the barnacle A. amphitrite. These results suggest that histamine may play an important role in regulating the larval metamorphic competence of the barnacle A. amphitrite, and the antihistamine compounds are promising potential nontoxic antifouling additives.