Long term ultraviolet treatment for macrofouling control in Northern and Southern hemispheres

Biofouling of marine structures must be controlled if crippling operational and maintenance costs are to be avoided and biological invasions prevented. However, traditional methods of biofouling control typically involve the use of toxic chemicals, which have their own drawbacks, both financial and environmental. For ships, the hull is the largest surface requiring a fouling-control coating, however there are other so-called ‘niche’ areas (up to 10% of total wetted area) that typically cannot be, or are not routinely, treated to prevent biofouling accumulation. The use of UV light is a tried and tested sterilization method that has been shown to also work underwater. However, the speed with which UV can be applied to large-scale biofouling control will be determined by the engineering challenges involved and the lack of basic understanding around the biological mode of action. The former is essential for effective translation of this established technology into a high-performance, industrially useful, fouling-control system. The latter will be important for environmental regulation and safe use as well as performance optimisation. Here, we developed two bespoke flow-through systems to replicate ship niche areas and deployed them in Melbourne, Australia, and North East England. We demonstrated a 40-90% reduction in biofouling coverage on silicone tiles embedded with UV-emitting LEDs, even as the LED output waned (after ~8000 hours). Image analysis and amplicon sequencing of 18S genes provided complementary information about the taxonomic composition of the fouling communities and highlighted some taxa, for example ascidians and diatoms, which may have, or in future develop, UV resistance. Interestingly, the UV treatment far exceeded performance estimates based upon the predicted attenuation distance of UV in seawater. Overall, while it is clear that UV treatment works in terms of its efficacy against the vast majority of observed fouling species, technical challenges remain, as do knowledge gaps surrounding the biological and ecological effects of widespread use.