Biofouling intensity in European waters: A compiled dataset and spatial assessment with focus on the Baltic Sea and...

Biofouling on ship hulls increases fuel consumption, greenhouse gas emissions and invasive species spread. For effective management, understanding the expected fouling pressure in the waters of interest is crucial. This study illustrates biofouling intensity by integrating published (2014-2024) and recent field data (2023-2024) from 35 locations across the Baltic Sea, Northeast Atlantic, Mediterranean Sea, and Black Sea. The weighted mean fouling ratings for these sites were assessed together with environmental parameters to identify factors explaining the observed results across different sea basins. Key findings indicate that the Mediterranean Sea sites (n=3) exhibit the highest indicative fouling intensity. A comparative analysis of the data-rich regions revealed that the Northeast Atlantic (n=14) exhibits significantly higher fouling intensity than the Baltic Sea (n=17) when sites with strong estuarine influence are excluded. Salinity was identified as the dominant factor influencing fouling pressure (R²=0.39-0.40), while dissolved oxygen, phosphate level and temperature showed weaker correlations (R²≤0.2). The presented spatial assessment can be used to manage ship hulls and maritime structures in port or marina areas and provides the first management baseline from existing European data. However, it highlights that the data-poor status of certain regions, alongside other knowledge deficiencies, remains a significant obstacle to unified pan-European management. Addressing these gaps is crucial for establishing a scientific basis for sustainable biofouling practices, in accordance with global initiatives such as the IMO Biofouling Guidelines and the EU Invasive Alien Species Regulation.