Survey on the terrestrial invertebrate fauna of Surtsey with special emphasis on 2007–2021

This paper summarises the results of standardised studies on the colonisation and succession of terrestrial invertebrate communities on Surtsey during 2007–2021, continuing from the previously published results from 2002–2006. Sampling has been carried out annually in mid-July using pitfall traps placed in permanent plots, supported by a Malaise trap in the gull colony and manual collection in various habitats. The aim has been to follow changes in the terrestrial invertebrate fauna and provide evaluation of species establishment in relation to habitat succession. In total, 410 species or species-equivalent taxa have been identified on Surtsey since the beginning of research there in 1965. Of these, 198 were regarded as settled, 33 of uncertain status and 179 not settled. Species composition and community structure were analysed by TWINSPAN and DCA ordination of material from 30 permanent plots. The results showed clear faunal differences between the well vegetated gull colony, the sand-filled lava areas, and the northern spit. The gull colony represented the most diverse habitat in terms of both specimens and species, strongly influenced by nutrient input from the breeding birds. Dipterans and hymenopterans represented the greatest diversity and specimen abundance, while staphylinid beetles and spiders were among the most successful colonisers. The succession of the terrestrial invertebrate communities followed the gradual formation of organic soil and denser vegetation cover, showing slow but steady change. This research was of great importance for understanding the colonisation of terrestrial invertebrate species and the development of their communities on newly formed volcanic islands.