Novel, non-toxic antifouling technologies are focused on the manipulation of surface topography to deter settlement of the dispersal stages of fouling organisms. This study investigated the effect of the aspect ratio (feature height/feature width) of topographical features engineered in polydimethylsiloxane, on the settlement of cyprids of Balanus amphitrite and zoospores of Ulva linza. The correlation of relative aspect ratios to antifouling efficacy was proven to be significant. An increase in aspect ratio resulted in an increase of fouling deterrence for both zoospores and cyprids. The spore density of Ulva was reduced 42% with each unit increase in aspect ratio of the Ulva-specific Sharklet AF™ topography. Similarly, the number of settled cyprids was reduced 45% with each unit increase in aspect ratio. The newly described barnacle-specific Sharklet AF™ topography (40 μm feature height, aspect ratio of 2) reduced cyprid settled by 97%. Techniques have been developed to superimpose the smaller Ulva-specific topographies onto the barnacle-specific surfaces into a hierarchical structure to repel both organisms simultaneously. The results for spore settlement on first-generation hierarchical surfaces provide insight for the efficacious design of such structures when targeting multiple settling species.

The incidence and severity of extraordinary macroalgae blooms (green tides) are increasing. Here, climate change (ocean warming and acidification) impacts on life history and biochemical responses of a causative green tide species, Ulva rigida, were investigated under combinations of pH (7.95, 7.55, corresponding to lower and higher pCO2), temperature (14, 18°C) and nitrate availability (6 and 150μmolL-1). The higher temperature accelerated the onset and magnitude of gamete settlement. Any two factor combination promoted germination and accelerated growth in young plants. The higher temperature increased reproduction, which increased further in combination with elevated pCO2 or nitrate. Reproductive success was highest (64.4±5.1%) when the upper limits of all three variables were combined. Biochemically, more protein and lipid but less carbohydrate were synthesized under higher temperature and nitrate conditions. These results suggest that climate change may cause more severe green tides, particularly when eutrophication cannot be effectively controlled.

Over the last decade, approaches to the development of surfaces that perturb settlement and/or adhesion by barnacles have diversified substantially. Although, previously, coatings research focussed almost exclusively on biocidal technologies and low modulus, low surface-free-energy ‘fouling-release’ materials, novel strategies to control surface colonisation are now receiving significant attention. It is timely, therefore, to review the current ‘state of knowledge’ regarding fouling-resistant surface characteristics and their mechanisms of action against settling larvae of barnacles. The role of the barnacle in marine fouling is discussed here in the context of its life cycle and the behavioural ecology of its cypris larva. The temporary and permanent adhesion mechanisms of cyprids are covered in detail and an overview of adult barnacle adhesion is presented. Recent legislation has directed academic research firmly towards environmentally inert marine coatings, so the actions of traditional biocides on barnacles are not described here. Instead, the discussion is restricted to those surface modifications that interfere with settlement-site selection and adhesion of barnacle cypris larvae; specifically, textural engineering of surfaces, development of inert ‘non-fouling’ surfaces and the use of enzymes in antifouling.