Marine biofouling is of major economic concern to all marine industries. The shipping trade is particularly alert to the development of new antifouling (AF) strategies, especially green AF paint as international regulations regarding the environmental impact of the compounds actually incorporated into the formulations are becoming more and more strict. It is also recognised that vessels play an extensive role in invasive species propagation as ballast waters transport potentially threatening larvae. It is then crucial to develop new AF solutions combining advances in marine chemistry and topography, in addition to a knowledge of marine biofoulers, with respect to the marine environment. This review presents the recent research progress made in the field of new non-toxic AF solutions (new microtexturing of surfaces, foul-release coatings, and with a special emphasis on marine natural antifoulants) as well as the perspectives for future research directions.

Marine macroalgae are particularly prone to epiphytism. The colonisation of their surface may lead to severe perturbations and sometimes to the death of the host. To protect themselves against settling and/or competing organisms, many algae have developed defences against fouling by producing a wide variety of chemically active metabolites. The goal of this study was to investigate potential anti-microfouling activities of two introduced algal species from the Brittany coast (France),Sargassum muticum(Phaeophyceae) andGrateloupia turuturu(Rhodophyceae). Thus, a complete study of the antimicrobial activities of extracts (aqueous, acetone, chloroform, dichloromethane, diethyl-ether, ethyl acetate, ethanol 96°, hexane and methanol) fromS. muticumandG. turuturuagainst marine fouling bacteria (5 strains), fungi (5 strains) and biofilm-associated microphytobenthic strains (5) were performed. The most active extract ofG. turuturuwas the dichloromethane fraction, while the chloroform extract fromS. muticumshowed some good results. Our data suggest that these macroalgae can provide useful compounds or templates for industrial anti-microfouling applications.

The sesquiterpene hydroquinone avarol (1) was isolated from the marine sponge Dysidea avara, whereas the corresponding quinone, avarone (2), was obtained by oxidation of avarol, and the significantly more lipophilic compounds [3’-(p-chloro-phenyl)avarone (3), 3’,4’-ethylenedithioavarone (4), 4’-isopropylthioavarone (5), 4’-tert-butylthioavarone (6), 4’-propylthioavarone (7), 4’-octylthioavarone (8)] were obtained by nucleophilic addition of thiols or p-chloroaniline to avarone. All these compounds were tested, at concentrations ranging from 0.5 to 50 μg/mL, for their effect on the settlement of the cyprid stage of Balanus amphitrite, for toxicity to both nauplii and cyprids and for their growth inhibitory activity on marine bacteria (Cobetia marina, Marinobacterium stanieri, Vibrio fischeri and Pseudoalteromonas haloplanktis) and marine fungi (Halosphaeriopsis mediosetigera, Asteromyces cruciatus, Lulworthia uniseptata and Monodictys pelagica).

Numerous marine organisms, including macroalgae, produce bioactive compounds. As chemical extraction processes do not distinguish between compounds originating from the alga and its associated microflora, a key step immediately prior to isolation of molecules, is elimination of epibionts from the alga studied. In chemical, ecological and biotechnological contexts, a clear identification of the source organism, when symbiotic interactions occurs, is crucial. We aimed to improve understanding of specific secondary metabolite production by macroalgae through development of a metho-dology for removing microbial epibionts immediately prior to chemical extraction without damaging algal cell surfaces (to avoid extraction of endogenous macroalgal compounds at this stage). Various solutions were tested: non-polar solvents (dichloromethane and hexane), alcohols (methanol, ethanol and isopropanol), oxidants (sodium hypochlorite, hydrogen peroxide and iodine) and a natural product (tea tree oil) at various concentrations and contact times. Five macroalgal species were employed: Chondrus crispus, Fucus serratus, Palmaria palmata, Saccharina latissima and Ulva lactuca. Scanning electron microscopy was used to evaluate the surface integrity. The best epibiont removal rate without damaging tissue was obtained with mixtures of ethanol (40–50%) and sodium hypochlorite (1%). Interestingly, macroalgal moisture content influenced treatment efficacy.