Anthropogenic pressure leads to more introductions: Marine traffic and artificial structures in offshore islands increases non-indigenous species

Anthropogenic pressures such as the introduction of non-indigenous species (NIS) have impacted global biodiversity and ecosystems. Most marine species spreading outside their natural biogeographical limits are promoted and facilitated by maritime traffic through ballast water and hull biofouling. Propagule pressure plays a primary role in invasion success mixed with environmental conditions of the arrival port. Moreover, with the current ocean sprawl, new substrates are offered for potential NIS recruits. Here, differences in the fouling assemblages thriving inside three different ports/marinas facilities in Madeira Island were assessed for comparison. The locations showed significant differences concerning assemblage structure. Most NIS were detected in plastic floating pontoons. Funchal harbour receives most of the marine traffic in Madeira, acting as the main hub for primary NIS introductions, being recreational boating involved in NIS secondary transfers. Our results highlight the need for future management actions in island ecosystems, particularly monitoring and sampling of recreational boating.

Automated summary

Anthropogenic pressures, such as the introduction of non-indigenous species, have had a significant impact on global biodiversity and ecosystems. This study assessed the differences in fouling assemblages within three different ports/marinas in Madeira Island, revealing significant variations in their structure. Plastic floating pontoons were found to have the highest number of non-indigenous species. Funchal harbour was identified as the primary hub for introducing these species, with recreational boating playing a role in secondary transfers. These findings highlight the importance of implementing management actions, particularly in island ecosystems, and monitoring recreational boating activities.