Monitoring arthropods under the scope of LIFE-SNAILS project: II - Santa Maria Island data with implementation of the Index of Biotic Integrity

The data presented here constitute an important component of the LIFE SNAILS project (Support and Naturalisation in Areas of Importance for Land Snails) which aims to protect three threatened endemic mollusc species from Santa Maria Island: two land snails ( Oxychilus agostinhoi Martins 1981 and Leptaxis minor Backhuys, 1975) and a semi-slug, Azorivitrina angulosa (Morelet, 1860). Although, arthropods are not direct targets of the project, their communities can provide useful indicators of overall habitat quality. A previous survey of mixed forests on Santa Maria provided the baseline for the present study, as the same sites were surveyed, except two additional sites incorporated in 2025. We obtained 55 sampling events from forests on Santa Maria between 16 June 2024 and 15 December 2025. A total of 20,282 specimens were collected, with 15,055 specimens identified to species or subspecies level, representing 74% of the total sample. Overall, 172 species and subspecies were identified: 27 endemic, 48 native non-endemic, 77 introduced and 20 of uncertain colonisation status. We recorded ten species new to Santa Maria Island. However, none represented a new record for the Azores Archipelago. Of these new island records, two were native non-endemic species, six were introduced and two had uncertain colonisation status. These new records include Campyloneura virgula (Herrich-Schaeffer, 1835), Carpelimus troglodytes troglodytes (Erichson, 1840), Hermetia illucens (Linnaeus, 1758), Nacaeus impressicollis (Motschulsky, 1858), Neobisium maroccanum Beier, 1930, Phyllotreta procera (Redtenbacher, 1849), Pilophorus confusus (Kirschbaum, 1856), Ploiaria chilensis (Philippi, 1862), Sophonia orientalis (Matsumura, 1912) and Textrix caudata L. Koch, 1872. Calculation of the Biotic Integrity Index (IBI) showed that SMR-SNAILS-T04 consistently recorded high values, whereas SMR-SNAILS-T08 exhibited the clearest decline over time. In this study, we extended the long-term monitoring of the mixed forests of Santa Maria by deploying SLAM (Sea, Land, Air, Malaise) traps and compiling a comprehensive database of all identified specimens collected between Summer 2024 and Autumn 2025.