Structure of Non-Indigenous Fouling Assemblages and Biocontamination Levels in Portuguese Recreational Marinas Under Different Salinity Conditions

The number of recreational marinas has increased in recent years due to the growing demand for leisure boating. Recreational marinas are key points for the introduction of non-indigenous species (NIS), which are considered a source of biocontamination. However, there is scarce knowledge on the influence of environmental features on NIS fouling assemblages, especially regarding different salinity conditions. The aim of this study is to explore the effect of salinity on the structure of NIS fouling assemblages and biocontamination levels. Therefore, fouling assemblages associated with floating pontoons were studied in recreational marinas located in fully marine and brackish habitats on the Northern Portuguese coast. Twenty-four NIS were found, of which arthropods and bryozoans represented the most abundant taxa. Except for NIS abundance, univariate and multivariate analyses showed that NIS assemblage structure was shaped by salinity conditions. Thus, NIS richness and the ratio between NIS richness and total richness were significantly higher in marine than in brackish habitats. Similarly, consistently higher biocontamination levels were found in marine habitats, compromising their ecological status. Quantitative data provided here will be useful in the development of NIS management strategies. Thus, in Northern Portugal, efforts should be focused on marinas under fully marine salinity conditions because they harbor a greater number of NIS and, consequently, a worse ecological status.