CIMPAL-based assessment of cumulative biological pressures from invasive alien species, jellyfish blooms, and harmful algal blooms in the Italian Adriatic Sea

Biological stressors increasingly threaten coastal and marine ecosystems. Invasive alien species (IAS), jellyfish blooms, and harmful algal blooms (HABs) are among the most widespread, yet their cumulative pressures are challenging to quantify. This study applies the Cumulative IMPacts of invasive ALien species (CIMPAL) index to assess the relative spatial patterns and intensity of these stressors in the western Adriatic Sea, drawing on validated observational and structured citizen-science data. Seven percent of the study area (4500km 2 ) showed cumulative pressure, with higher CIMPAL scores in coastal than offshore waters and spatially localised rather than widespread patterns. Hotspots were found in the northern and central Adriatic Sea, mainly due to the co-occurrence of IAS and jellyfish blooms while HABs were more restricted to lagoons and deltas. Non-parametric tests revealed significant spatial differences among Adriatic sectors. These results reflect potential cumulative pressure rather than measured ecosystem degradation and highlight the value of incorporating citizen science data while acknowledging its limitation. Findings support integrated, multi-stressor management under the Marine Strategy Framework Directive (MSFD).