Chapter 107 - Shallow subterranean habitats

Abstract

Shallow subterranean habitats (SSHs) are aphotic subterranean habitats relatively close to the surface (<10m) with habitable spaces larger than the animals themselves, and with a fauna that includes species adapted for subterranean life, including loss of eyes and pigment. There are four aquatic SSHs—seepage springs, epikarst, calcrete aquifers, and hyporheic habitats. Seepage springs are the shallowest of all SSHs, with the habitat rarely extending even 1m in depth. Many terrestrial SSHs are collectively called milieu souterrain superficiel (MSS), and consist of the spaces between rocks, rock cracks and the like. Other terrestrial SSHs include soil, lava tubes, and iron ore caves. All of these habitats are more variable than caves, typically with a pronounced annual temperature cycle. Available organic matter is also higher in SSHs than in caves. The importance of SSHs as gateways to the subterranean realm is not known, but it is clear that they contain species both modified for subterranean life, and unique to these habitats.