Barnacle Settlement on Hydrogels

Settlement of cultured Balanus amphitrite cyprid larvae was tested on different non-solid hydrogel surfaces. Gels consisting of alginate (highly anionic), chitosan (highly cationic), polyvinyl alcohol substituted with light-sensitive stilbazolium groups (PVA-SbQ; very low cationic) and agarose (neutral) were applied in cell culture multi-well plates. Polystyrene served as a solid surface reference. Preliminary experiments were performed to determine whether any substances leaching out of the gels could inhibit barnacle settlement. Whilst leachate from the gels revealed no toxicity towards Artemia salina nauplius larvae, PVA-SbQ in solution at and above a concentration of 0.4 ppm inhibited B. amphitrite cyprid settlement. Gels were therefore washed to avoid such effects during further testing, and toxicity and settlement tests with B. amphitrite nauplii and cyprids, respectively, applied to verify that washing was effective. Settlement was tested directly on the different test materials, followed by a quality test of non-settled larvae. All gels inhibited barnacle settlement compared to the polystyrene controls. Gels consisting of 2.5% PVA-SbQ or 0.5% agarose showed promising antifouling properties. Although some settlement occurred on 2.5% PVA-SbQ gels, metamorphosis was clearly inhibited. Only 10% of the larvae had settled on 0.5% agarose gels after 8 d. Less than 40% settlement occurred on alginate gels, as well as on 2% chitosan gels. Quality testing showed that the majority of remaining non-settled larvae in all gel experiments were able to settle when offered a suitable solid substratum.