The effect of temperature and water level variations on the distribution and abundance of aquatic invertebrates in two cave streams and their resurgence

This study shows how populations of aquatic invertebrates in two cave streams (1812 and Organ Main Stream) and their resurgence are affected by the hydrologic regimes of their habitat. Monitoring hydrologic variables such as water level, temperature, and response to precipitation recorded at the resurgence revealed significant differences in both cave streams. 1812, the colder of the two, showed dramatic peaks in both temperature and stage immediately following rain events, while Organ Main Stream had a more subtle response which lagged precipitation by several hours. A diurnal temperature cycle and post-storm fluctuations in temperatures and water levels were characteristics of the spring. Examination of the biological data revealed that 1812 had a highly variable community consisting of both epigean and hypogean animals which varied in numbers and composition throughout the course of study. Gammarus minus was the only inhabitant retrieved from Organ Main Stream. The population of G. minus in Organ was both smaller and less variable than 1812. The resurgence, whose hydrological regime was more stable than 1812, also had a large, stable G. minus population. This study concluded that stability of cave hydrology was crucial in determining community size and stability of ecologically sensitive organisms such as G. minus.