Introduction

The antarctic cryptoendolithic microbial ecosystem lives under sandstone surfaces in the dry valley region (Friedmann and Ocampo,1976; Friedmann, 1977). It is relatively simple, consisting of cyanobacterial or algal primary producers, fungal consumers, and bacterial decomposers. It lacks animals and, possibly, also archaea. With rock temperatures rising above 0 °C only for a few weeks in the austral summer to allow photosynthetic productivity, this ecosystem is permanently poised on the edge of existence.

Before we talk about these specific rock-inhabiting organisms, it is useful to be familiar with all lithophytic life forms. Epilithic organisms live on rocks. Endolithic organisms grow inside rocks, with three subcategories that denote the mode of entry or the presence or absence of a protective surface crust (Golubic et al., 1981). Euendolithic algae and cyanobacteria actively bore into limestone in the intertidal zone and, occasionally, in deserts (Friedmann et al., 1993a; Garty, 1999). Chasmoendolithic organisms occupy weathering cracks and fissures in a variety of rocks. Cryptoendolithic organisms colonize pre-existing pore spaces in translucent rocks, most commonly sandstones (Friedmann and Ocampo-Friedmann, 1984; Bell, 1993, Nienow et al., 2002; Omelon et al., 2006). The colonized zone, in this case, is covered by a silicified surface crust.