The terrestrial micro-arthropod fauna of the South Sandwich Islands

The South Sandwich Islands are an isolated maritime Antarctic volcanic isla nd are 550-600 km south-east of South Georgia. The terrestrial biology of t he islands, with emphasis on the unique habitats associated with volcanical ly warmed ground, was investigated in 1997 and compared with the data colle cted during the only previous (1964) terrestrial expedition to the archipel ago. The terrestrial fauna includes 29 free-living micro-arthropod species (nine Collembola and 20 Acari) and two, currently unidentified, enchytraeid worms; a further eight parasitic and sublittoral Acari are recorded in the literature. Freshwater habitats are very restricted in the archipelago and no freshwater fauna was located. Supralittoral pools on a single island co ntained the marine isopod Cassidinopsis maculata. There are no endemic taxa and no shoreline invertebrates other than the supralittoral Archisotoma br ucei (Collembola) and two Enchytraeidae. Diversity on individual islands is , in part, a function of available ice-free ground area. The majority of do minant species throughout the archipelago, Cryptopygus antarcticus (Collemb ola), Nanorchestes nivalis, Eupodes minutus, Alaskozetes antarcticus and Ha lozetes belgicae (Acarina), originate on other maritime Antarctic islands, while Ayersacarus tilbrooki (Acarina) is sub-Antarctic. Few (one to three) individuals of several other sub-Antarctic species were recorded by either 1964 or 1997 expeditions, but only Pilellus rykei (Acarina) was reported by both. None of the sub-Antarctic species thought to be associated with geot hermally warmed ground in 1964 was confirmed in 1997, despite extensive sam pling of the same sites. It is more probable that sub-Antarctic colonists f requently arrive on the South Sandwich Islands but are unable to establish long-erm viable populations. Cryptopygus caecus, now widespread on Candlema s I., is a solitary exception to this generalization.