Refining management strategies in marine protected areas in oceanic islands: a non-indigenous species risk index for strategic prioritization

Non-indigenous Species (NIS) pose significant threats to marine biodiversity globally, especially in ecologically sensitive habitats such as Marine Protected Areas (MPAs). This study uses data collected in the Autonomous Region of Madeira (North Atlantic), Portugal, to create a spatial model aiming to (1) develop a spatially explicit index of NIS dispersal from known hotspots such as ports, harbours, marinas, and anchoring areas; (2) assess the relative vulnerability of Madeira's MPAs to local NIS dispersion and establishment; and (3) provide insights for a scalable NIS monitoring framework and evaluating invasion risks. The spatial model integrates maritime traffic intensity and proximity to NIS hotspots, using a straightforward approach that can be applied in data-limited contexts. While designed to address Madeira's regional challenges, the model is adaptable to other biogeographic contexts and can incorporate additional complexity, such as species-specific traits or ecological layers, to suit different settings. Our findings underscore the role of maritime infrastructure and vessel traffic in NIS spread, revealing the vulnerability of Madeira's MPAs due to insufficient ecological monitoring and the absence of NIS monitoring and early detection programs. This study provides practical recommendations for improving MPA management and mitigating NIS risks, contributing to regional conservation efforts. Additionally, it establishes a baseline risk assessment approach that can be customised and expanded to guide NIS management and biodiversity conservation in other regions, particularly those with similar challenges.