Abundance and seasonality of mid-altitude fellfield arthropods from Marion Island

Fellfield is an important habitat in both the Antarctic and sub-Antarctic. However, few studies have examined the abundance and seasonality of arthropods in sub-Antarctic fellfield habitats. Here, soil arthropod communities were sampled for over a full year in two distinct habitat components (rocky areas and Azorella selago cushions) in a mid-altitude fellfield on Marion Island. Species richness was relatively high (42 spp.) and consisted almost exclusively of indigenous species. Maximum mean annual density in the A. selago cushions was 16,000 individuals m^-2 for Eupodes minutus. In contrast, the highest density of any species in the rocky, inter-cushion areas was 700 individuals m^-2 for Halozetes fulvus. Quantitative analyses highlighted prominent differences in arthropod community structure between the two habitat components, despite the fact that most species were common to both of them. In general, arthropod abundances were lower in the fellfield compared with less extreme vegetation types in the sub-Antarctic, but were not dissimilar to those found in fellfield in the maritime Antarctic. In the Marion Island fellfield, arthropods either showed no pronounced seasonal peak in abundance, or a summer peak, although these patterns differed between habitat components within species, and between species. These data provide a firm quantitative foundation for further investigations of community patterns and seasonality in sub-Antarctic fellfield arthropods.