Mite and insect zonation on a Marion Island rocky shore: a quantitative approach

This study provides the first quantitative analysis of the littoral and sup ralittoral insect and mite assemblages of sub-Antarctic Marion Island. Seve nteen mite species (126,203 individuals) from 11 families were found on the shore at Macaroni Bay. Three families dominated the assemblages in both ab undance and diversity: the Hyadesiidae, Ameronothridae and Halacaridae. Six insect species from three orders were found on the shore. Species richness increased from one in the littoral, to four and two species in the Mastodi a and Caloplaca zones, respectively. The littoral chironomid midge Telmatog ton amphibius was the most abundant insect species, constituting 80% of all insects counted. Arthropod assemblages corresponded closely to the cryptog am-dominated zonation patterns previously identified for the Marion Island shore. This clear association between arthropod and cryptogam zonation patt erns provided a clear indication of habitat specificity in many of the spec ies, and a quantitative analysis of habitat specificity on a species by spe cies basis supported this idea. The specificity of most species to the shor e, which forms part of the epilithic biotope, is most Likely a consequence of the considerable age of this biotope compared to the younger, post-glaci al vascular vegetation. Tourist species, i.e. species transient to an assem blage, inflated species richness in zones and the distribution ranges of sp ecies across zones. It is suggested that previous qualitative analyses of s horeline arthropod communities may have overestimated species ranges and ri chnesses because of the inclusion of tourist species. It is suggested that if a sound understanding of patterns in, and processes underlying Antarctic arthropod assemblages is to be achieved, quantitative analyses must be exp anded in the region.