Arthropod Communities in a Maritime Antarctic Moss-Turf Habitat: Three-Dimensional Distribution of Mites and Collembola

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Abstract
Five sets of 96 contiguous samples were cut from a moss-turf habitat on Signy Island in the maritime Antarctic. Ten taxa of arthropods (Acari and Collembola) were extracted, and 6 occurred frequently enough for analysis. The vertical distribution of these 6 taxa indicate that 3 occur near the surface of the moss-turf, 2 in an intermediate position and 1 deep down. Within a taxon the vertical distribution varies from one developmental stage to another. Aggregation is the norm in this community, but its degree varies with the developmental stage (prostigmatid mites). The predator, Gamasellus racovitzai, is generally randomly distributed. Since species differ in their vertical distributions, many correlation coefficents between the counts of individuals for species pairs are negative. When the effect of depth is eliminated, similar correlation coefficents are frequently positive and never both significant and negative. Two separate subcommunities of arthropods can be recognized: these are termed the green moss community and the dead moss community. The former occurs near the surface of the moss-turf (0-1.5 cm layer), the latter deeper in the turf (below 3 cm). The 2 subcommunities are composed of the same 6 spp., but the relative proportions of the species differ considerably. The numbers of individuals of a species in one community are generally not correlated with the numbers of the same species in the other community and, hence, aggregations in the 2 communities are independent of each other.