The fouling hydroid Ectopleura larynx: a lack of effect of next generation antifouling technologies

The hydroid Ectopleura larynx is one of the main fouling organisms on salmon aquaculture cages in Norway; this study investigated novel surface materials and microtopographies to deter its settlement. The settlement preferences of hydroid larvae for 12 materials with wettabilities ranging from hydrophobic (54°) to hydrophilic (112°) were tested in a no-choice bioassay. Although settlement differed between materials, with the highest average settlement on polytetrafluoroethylene (95%) and the lowest on untreated polyurethane (53%), no trend regarding the tested wettabilities could be found and none of the tested materials was able to reduce average settlement below 50%. Furthermore, nine high-density polyethylene (HDPE, 100–600 μm microtopographies) and seven polydimethylsiloxane (PDMS; 40–400 μm microtopographies) microtextured surfaces were tested. There was no systematic effect of microtopography on the settlement of E. larynx larvae. However, there was a preference for settlement in channels on PDMS mi...