Mapping Presumptive Habitat for Subterranean Aquatic Species of Concern

Generally, populations of species of concern are located by direct observation or capture. This is a severe limitation when dealing with cavernicoles, since a very small percentage of potential habitat is accessible to investigators. The Ozark Underground Laboratory is promoting the concept of presumptive habitat; that is all groundwater that has subsurface hydrological interconnections should be presumed to contain the aquatic species of concern that are found in accessible parts of the groundwater system and that the entire groundwater system be managed accordingly. Groundwater tracing using fluorescent dyes is a powerful, empirical tool for delineating groundwater basins and demonstrating hydrological interconnections between groundwater basins. The recharge area boundaries representing known and presumptive habitat are important tools for biological analysis and conservation management. Dye traces help evaluate tested portions of the groundwater system; dye passes readily only through relatively open conduits; a significant requirement for most aquatic cavernicoles. Aquatic cavernicoles can generally move against the hydraulic gradient and cross drainage divides under more variable flow conditions than does tracer dye. The migration of fauna against the hydraulic gradient permits more gene flow than may be suggested by dye tracing.