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.