The land-invertebrate fauna on Surtsey during 2002–2006

Formal studies on invertebrate colonizers and establishments on Surtsey started in 1965 and the island was visited regularly for longer and shorter periods till 1984. After a period of sporadic invertebrate studies, yearly visits to Surtsey started again in 2002. Here are presented the results from a five year study period, 2002–2006. Surtsey is characterized by three kinds of substrates, viz. lava, sand and palagonite rock. The invertebrate collecting is mainly based on pitfall trapping in permanent plots on sand and lava substrates, also informing on the impact of a gull breeding colony that started in the lava field in 1985. Netting and direct picking takes place on all three kinds of substrates of the island. Also, three traps were set up close to the hut and helicopter platform to test for signs of human impact. Hitherto, 354 species or taxa ranked as species have been found on Surtsey. Thereof 144 are regarded permanent settlers. in 2005 an invasion of flying insects by air mass was witnessed. Transport of invertebrates by birds was probably underestimated in the beginning, but the existence of a number of permanently settled species can hardly be explained differently. The gull breeding colony was an advantage to the invertebrate diversity on Surtsey. Higher species diversity is found within the colony than outside it and a clear distinction in species composition between plots outside and within the gull colony. Also, a great faunal diversity is within the colony while the fauna is rather homogenous on the sand substrate. Land-invertebrates have proved to play a very important role in the developing ecosystem on the island, also forming the basis for colonization of invertebrate feeding birds.