Anti-settlement activity of marine-inspired micropeptides against model soft and hard macrofoulers Ciona savignyi and Amphibalanus improvisus.

The current study describes the evaluation of 16 synthetic linear tripeptides combining structural elements from the innate defence system with brominated amino acids often found in antifouling compounds isolated from sessile marine organisms. These organisms have clean exteriors and their chemical arsenal of natural antifoulants is interesting from an antifoulant design perspective. The peptides were evaluated for their ability to inhibit the settlement and metamorphosis of the soft and hard macrofoulers Ciona savignyi and Amphibalanus improvisus which are two key macrofoulers challenging to remove once established. It was shown that the evaluated compounds were generally highly active antifoulants with low micromolar IC50-values against both fouling organisms via different mechanisms. Several of the compounds were shown to be biocidal against Ciona savignyi larvae at the lowest evaluated concentration (1 µM). Against Amphibalanus improvisus, a non-biocidal antifouling effect was generally observed with the most potent compound displaying an IC50-value of 0.5 µM. The study illustrated how these two groups of natural compounds combined are highly bioactive and can yield highly efficient antifoulants.