Marine Biofouling Control by Ultraviolet Light: Development, Ecological Impact and Genomic Assessment

Abstract

Biofouling is an issue for any surface within the marine environment, causing environmental and financial ramifications. The harmful effects of ultraviolet (UV) light have been well documented in the literature. Its use as an antifoulant, however, is at a developmental stage. Recent technological advancements have produced smaller and more affordable components which can be developed into new innovations. This study investigated the potential of UV B/C (265-300nm) light-emitting diodes (LEDs) for biofouling prevention. This was achieved by the production and analysis of a reproducible system for UV delivery, determination of irradiance thresholds of effect, analysis of UV damage and diatom repair mechanisms, including genotoxicity, and evaluating biofouling control during field deployments over 12 months and at two environmentally distinct locations. The development of a UV LED-embedded tile system was challenging with initial designs requiring improvements in surface coverage by UV radiation. Tile developments included producing high irradiance capacities and coverage of target surfaces. Highly turbid conditions were found to restrict the transmission of UV from the tile’s surface to < 1cm. Although transmission was recorded up to 14cm in the clearest conditions, the effective threshold was within a working range up to 5cm from the surface. LED integration for UV supply was successful and analysis indicated high capacities whilst minimising exposure towards nontarget organisms. The specific UV threshold for effect on the marine diatom Navicula incerta was explored by comparing UV exposure at different duration, pulsing and intensity conditions. Continuous exposure over long periods achieved progressively lower biomass of biofouling. Growth reductions were achievable after 2 hours and growth suppression of 87% was recorded after 24 hours. LED pulsing restricted growth compared to controls in all duty cycles trialled, however, duty cycles required a fluence between 0.94 and 2.34 J/cm2 to reduce biomass. High irradiance intensities produced greater reductions in biomass more readily than at lower irradiances. Using all three methods, specific doses for the prevention of growth of N. incerta were determined to be 20-42 J/cm2 depending on the delivery method. Cyclobutane pyrimidine dimer (CPD) formation and photoactive repair for N. incerta were quantified at specific irradiance exposures. A linear effect was visible for both damage over time and photoactive repair. Peak CPD concentrations of ~ 180 µg/ml-1 were reached after 24 hours of exposure; this was reduced by over 45% during a 24-hour repair period. Mutations ii forming single nucleotide polymorphisms (SNPs) were less prominent in the higher exposure samples. Higher SNP counts found in low-exposure treatments suggest that organisms were not resilient to exposures over 60 minutes. A comprehensive field study revealed the effectiveness of UV during practical application and the extent to which the system was able to operate. The photographic analysis determined a wide range of taxa, ranging from tunicates to tube worms, which colonised controls but were prevented within irradiated chambers. Biological restrictions were reproducible in two distinct geographical locations (Melbourne, Australia and Hartlepool, UK) displaying the universal nature of the application. The metagenetic analysis gave an insight into the microscopic biosphere indicating distinct eukaryotic and prokaryotic community structures. This project successfully developed and tested an innovative UV tile in two biogeographically distinct locations. The technique displayed a wide spectrum of prevention on fouling taxa including the model species N. incerta. This study determined thresholds of effect, mutagenic response and organism resilience. Understanding these biological impacts is paramount when determining the feasibility of a new technology