Tides of change: monitoring NIS in Icelandic harbours

Non-indigenous species (NIS) profoundly influence marine ecosystems globally. Our study examines NIS prevalence in Icelandic harbours, focusing on species richness and community composition of fouling species. Using settlement plates, we demonstrate NIS dominance, particularly of non-indigenous ascidians, aligning with global trends. The dominant species varied from year to year, likely influenced by environmental conditions, propagule pressure, and already established species. The escalation of maritime traffic, particularly in southwest Iceland, amplifies propagule pressure, thereby facilitating the establishment of NIS populations. Consequently, local maritime traffic can promote their further spread to other regional localities. Additionally, we documented three new bryozoan records for Iceland, highlighting the necessity for further biogeographic research. Cryptogenic species, comprising a notable portion of the fouling community, pose challenges to the understanding of biogeography and invasion ecology. Our findings emphasize the intricate dynamics of fouling communities in Icelandic harbours, underscoring the need for ongoing monitoring and management amidst environmental change and biological invasions.