A 7000-year record of oribatid mite communities on a maritime-antarctic island: Responses to climate change

We studied the fossil remains of the common Antarctic oribatid mites, Alaskozetes antarcticus and Halozetes belgicae, in sediment cores from two lakes in adjacent catchments on Signy Island, South Orkney Islands, maritime Antarctic. The aim was to examine the response of these species to 7000 yr of documented environmental change. Mites colonized the island shortly after the ice sheet retreated and habitats became available. A temperate period in the Holocene (c. 3800-1400 cal. yr BP) led to population expansion by factors of 7 (both species) in one catchment and 5.1 and 2.3 for both species in the other. This mid-Holocene hypsithermal is thought to have involved increases in habitat size, productivity, temperature, and moisture availability. Mite populations went into decline as conditions cooled. A period of short cold summers from c. 1400 cal. yr BP persisting to the middle of this century continued to impose restrictions on the biota. These results suggest that mite populations will respond positively to the recent rapid regional warming documented in the maritime Antarctic. However, on Signy Island this prediction is complicated by a similarly recent and rapid expansion of the populations of Antarctic fur seals (Arctocephalus gazella), which has not occurred previously since deglaciation, damaging the mites' habitats and exerting a new set of ecological constraints.