The data presented here is part of a doctoral project aimed at characterising and comparing arthropod diversity across biotic communities in coastal ecosystems. The present work provides an inventory of the arthropods recorded in two coastal grasslands ecosystems: the Portugal mainland and the Azores. Sampling was conducted on São Miguel Island (Azores Archipelago) as well as in the Sesimbra and Sines regions (Setúbal District, mainland Portugal). Thirty-one plots were set and visited four times, in spring and summer of 2022.

The specimens collected were sorted and catalogued into a total of 534 arthropod species and morphospecies. In total, 67 species were common to both ecosystems. A total of 13,515 specimens were counted in the two coastal grasslands. We registered three new records for the Azores (in São Miguel Island), all being exotic: Aritranis director (Thumberg, 1822) (Hymenoptera, Ichneumonidae), Draeculacephala bradleyi, Van Duzee, 1915 (Hemiptera, Cicadellidae) and Isodontia sp. Patton, 1880 (Hymenoptera, Sphecidae). This publication demonstrates the importance of coastal grasslands as reservoirs for some potentially invasive arthropod species.