Monitoring of potential invasive arthropod species in Azores Islands (Corvo, Flores, Faial, Pico, Terceira, São Miguel and Santa Maria): the PRIBES Project

Arthropods provide essential ecosystem services, yet multiple lines of evidence indicate widespread declines driven by habitat loss (degradation, fragmentation and reduction), biological invasions and climate change. Oceanic islands are particularly vulnerable to invasive alien species because of their isolation, small area and sensitivity to novel predators, competitors and pathogens. In the Azores, historical land-use change has greatly reduced native forest cover, while long-term monitoring indicates that introduced arthropod diversity is increasing even where total richness appears stable. However, ruderal coastal habitats (i.e. transitional, frequently disturbed environments often dominated by opportunistic exotic plants) remain comparatively under-sampled and may function as early “gateways” for new arthropod introductions. The PRIBES project intends to contribute to "The Regional Strategy for the Management of Terrestrial and Freshwater Exotic and Invasive Species in the Azores" (PRIBES-LIFE-IP- Estratégia regional para o controlo e prevenção de espécies exóticas invasoras - no âmbito do projeto LIFE IP AZORES NATURA, LIFE17 IPE/PT/000010). The PRIBES project addresses this gap by surveying arthropod assemblages associated with vascular plants in disturbed coastal ruderal habitats across multiple Azorean islands (Corvo, Flores, Faial, Pico, Terceira, São Miguel and Santa Maria) using a standardised time-based plant beating protocol, enabling comparisons of richness and colonisation status (endemic, native or exotic) amongst islands and vegetation contexts. This manuscript provides a standardised, multi-island synthesis of arthropod sampling across seven Azorean islands, encompassing 78 sites sampled with standard methods plus one site with ad hoc samples and 23,547 specimens. It reports 366 taxa, including 247 taxa identified to species/subspecies and 119 not identified morphospecies, delivering an unusually comprehensive archipelago-scale baseline for ruderal and edge-associated assemblages. The substantial unidentified morphospecies fraction, plausibly dominated by as-yet-unrecorded Azorean arrivals despite extensive local expertise, is consistent with documented increases in island exotic arthropod diversity and highlights an identification bottleneck where recent introductions and potential pests accumulate. The study also provides major distributional updates, including 62 new island records and one new record for the Azores, corresponding to the theridiid spider Dipoena melanogaster (C. L. Koch, 1837). By summarising colonisation status for all identified taxa, we show a strong contribution of introduced taxa (121 of 247 identified taxa) alongside endemic (37) and native non-endemic (72) components, offering a clear quantitative snapshot of assemblage structure relevant to biosecurity and conservation planning. In addition, for 17 taxa, the colonisation status is uncertain. By publishing openly accessible, standardised occurrence records, these data directly support early detection and surveillance prioritisation for emerging introductions and help provide information for management and biosecurity strategies in rapidly changing island landscapes.