Formation of Hypoxic Boundary Layers and Their Biological Implications in a Skin-Breathing Aquatic Salamander, Desmognathus quadramaculatus

We examined hypoxic boundary layers surrounding the skin-breathing aquatic plethodontid salamander Desmognathus quadramaculatus and investigated the flow regime in the natural habitat of this species. In slow-flowing water (<10 cm · s⁻¹), which we found to be the preferred microhabitat in nature, the boundary layer is the major resistance to oxygen uptake. Consequently, Po2 at the skin surface in slow-flowing water falls below 60 Torr even though Po2 in the free stream exceeds 150 Torr, and aerobic metabolism is severely impaired. Four salamanders survived reduced aerobic metabolism for 4 mo in the laboratory, implying that D. quadramaculatus can severely restrict overall metabolic needs and/or makes extensive use of anaerobic metabolic pathways.