Cumulative Negative Impacts of Invasive Alien Species on Ma-Rine Ecosystems of the Aegean Sea

Biological invasions are a human-induced environmental disturbance that can cause major changes in ecosystem structure and functioning. Located in the northeastern Mediterranean basin, the Aegean Sea is a hotspot of biological invasions. Although the presence of alien species in the Aegean has been studied and monitored, no assessment has been conducted on their cumulative impacts on native biodiversity. To address this gap and identify the most highly impacted areas and habitats and the most impactful invasive species in the Aegean, we applied the CIMPAL index, a framework developed for mapping the cumulative impacts of invasive species. Coastal habitats showed stronger impacts than the open sea. The highest CIMPAL scores were four times more frequent in the South than in the North Aegean. Shallow (0-60 m) hard substrate was the most heavily impacted habitat type, followed by soft substrates and seagrass meadows. We identified Caulerpa cylindracea, Lophocladia lallemandii, Siganus spp. and Womersleyella setacea as the most im-pactful species across their range of occurrence in the Aegean but, ranking varied depending on the habitat and impact indicator applied. Our assessment can support marine managers in prioritizing decisions and actions to control biological invasions and mitigate their impacts in the Aegean Sea.