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**Figure 5.** Anti-settlement activity of gallic acid persulfate (GAP) towards *Mytilus galloprovincialis* larvae after direct incorporation (DI) and chemical immobilization (CI) in commercial marine coatings. PU: polyurethane; PDMS: polydimethylsiloxane; h: hours. \* No larval settlement was observed for the PDMS-based coated wells.

In the experiments with the PDMS-based AF marine coating formulations, a high anti-settlement effect was observed in the wells coated with the control formulation, which can be explained by the coating's intrinsic non-stick properties [39]. This experimental approach with PDMS is thus not informative regarding the efficacy of GAP, but contributes to the understanding that this matrix is, per se, highly effective against mussel larvae attachment.

Thus, to better assess the influence of the presence of GAP in the coatings' anti-settlement properties, and also to overcome any masked effect from the intrinsic properties of the marine coatings, complementary assays with other optimized formulations of acrylic (AV) and room-temperaturevulcanizing (RTV)-PDMS-based non-marine coatings, were performed (c.f. Table 4). In the future, in situ tests will be performed to demonstrate the real potential applications of GAP-containing marine coatings in different AF systems worldwide.

**Table 4.** Non-marine coatings formulations with immobilized gallic acid persulfate (GAP).


AV: acrylic; CI: chemically immobilized; DI- directly incorporated; RTV-PDMS: room-temperature-vulcanizingpolydimethylsiloxane; TZA: triaziridine propionate crosslinker.

The anti-settlement studies with these new coatings (Figure 6) showed that, despite some decreases in larval settlement were observed in DI coatings, the CI GAP in both AV and RTV-PDMS-based formulations showed significant anti-settlement activity (*p* < 0.05), increasing the antifouling performance of both coatings even more, with only 15 and 0% of larvae adhesion being observed after 40 h of exposure, respectively.

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**Figure 6.** Anti-settlement activity of gallic acid persulfate (GAP) toward the macrofouling organism *Mytilus galloprovincialis larvae* after direct incorporation (DI) and chemical immobilization (CI) in conventional coatings. AV: acrylic; RTV-PDMS: room-temperature-vulcanizing polydimethylsiloxane; h: hours. \* Indicates significant differences at *p* < 0.05 (Dunnett test) against the negative controls (AV and RTV-PDMS).

Overall, GAP was responsible for the reduction in the settlement of a problematic marine fouling organism in different polymeric coatings after being chemically immobilized. With this optimized non-release immobilization, this very polar compound might be promising as an environment-friendly alternative resource to replace harmful commercial biocides in AF marine coatings.
