Inventory of potential new anti-fouling strategies inspired by nature

Abstract

As part of the Dutch Top consortia for Knowledge and Innovation (TKI) project 'Re-Drag with Nature' an inventory was made of the strategies that sea weeds apply to reduce the settlement and development of fouling organisms on their surface. This inventory was made based upon available literature and the results were assessed for their potency to protect man-made structures against biofouling. The reason for the focus on seaweeds was initiated by the observations that fouling pressure on seaweeds is in general low, and further supported by the knowledge that a lot of effort is currently being made to cultivate seaweeds and to utilise the compounds that can be extracted from it. However, the inventory was not fully limited to seaweeds. Where it inspired the thinking of new alternatives these were also briefly assessed. Seaweeds make use of physical and chemical strategies to keep their surface free of biofouling organisms. The physical strategies are based on the continuous renewal of surface material and are, therefore, not considered applicable to protect man-made structures without continuous maintenance. Self-polishing coatings are available for ship hulls, but these are only effective in combination with biocides. An alternative physical process that is not applied by seaweeds, but that may have the potency to reduce fouling is a combination of flow velocity and surface structure that could prevent early stages of fouling organisms from attaching to a surface. As this requires a controlled environment, it is not applicable to ship hulls or maritime infrastructure. It could work in industrial cooling water systems, but as the current methods that are applied there seem to fulfil the needs of the industry, this option was not further investigated. The chemical anti-fouling strategies of seaweeds are based on the production of a broad range of metabolites with the potential to reduce settlement and/or development of fouling organisms. Although the effectiveness of several of these metabolites has been shown on experimental scale, commercial application of bio-based compounds for anti-fouling purposes does not seem attractive, due to the high costs that are related with legislation/registration procedures for new chemicals. Apart from producing anti-fouling metabolites themselves, seaweeds can also support specific microbes that have little or no negative impact on their condition, but that prevent the settlement of more harmful species. A similar strategy, where a fouling species with low negative impact is favoured and supported, can have potential to manage fouling in an environmental friendly way on man-made surfaces where some drag is acceptable. As far as we are aware this is a completely new approach to deal with biofouling. When writing this report a proposal for a joint industry project (JIP) is being prepared that aims to investigate the potency of this approach to manage bio-fouling on offshore infrastructure.