Underwater Warfare: Antifouling Coatings vs. Biofilm in South Australia

Antifouling materials aim to prevent the accumulation of marine organisms on surfaces exposed to water, such as ship hulls and offshore structures. Their efficacy not only helps maintain the structural integrity and durability of submerged surfaces but also plays a crucial role in preventing the spread of invasive species and protecting marine ecosystems. This study examined five diverse antifouling coatings and an epoxy control to assess their performance at a key naval port in the Port Adelaide River, South Australia. Antifouling coatings with differing active biocides and fouling control mechanisms were chosen including: 1) Copper oxide and Copper pyrithione; 2) Copper thiocyanate and Zinc thiocyanate 3) Copper pyrithione fouling release coating; 4) non-biocidal fouling release coating; 5) Copper oxide and Zineb. These five coatings and epoxy controls were immersed for 4, 14, 25, and 36 weeks. A fully replicated set of samples was also deployed south of the river mouth, at the Cruising Yacht Club of South Australia, as a comparison. Water quality parameters were monitored fortnightly, and microbial communities in water and on the coatings were analysed through 16S rRNA sequencing and scanning electron microscopy. Seasonal and spatial variations were observed in the community structure, with temperature and turbidity being the primary drivers of the differences observed. All antifouling coatings prevented macrofouling for the duration of the immersion. Some significant differences in the microfouling communities were observed on the 1) Copper oxide and Copper pyrithione, 3) Copper pyrithione fouling release coating and 5) Copper oxide and Zineb between ANI and CYC. Immersion duration and seasonality resulted in significant differences in the attached organisms on four of the five coatings (1, 2, 3, 5) along with the epoxy between each site. This study advances understanding of site-specific microbial interactions with antifouling surfaces and provides avenues for early control of the settlement of macrofouling organisms.