Adaptations: Low oxygen

Abstract The ability to withstand and recover from long periods of stress is a critical adaptation for the colonization by and/or survival of any organism in harsh environments. Subterranean habitats exhibit high temporal and spatial patchiness of oxygen availability, resulting from a lack of autotrophicproduction and sporadic, unpredictable, and allochthonousinput. This chapter begins by examining the oxygen status of different groundwater systems including deep- and shallow- water-tableaquifers and the hyporheic zoneof streams. Then, based on laboratory studies, we examine the ecophysiological(i.e., behavioral, respiratory, and metabolic) responses of groundwater organisms, especially crustaceansand amphibians, to low oxygen concentrations. Finally, we suggest that, despite a strong tendency toward morphological and ecophysiologicalconvergence, subterranean organisms do not form a homogeneous group.