Responses to acute and chronic desiccation stress in Enchytraeus (Oligochaeta: Enchytraeidae).

Enchytraeids are small soil living oligochaete worms with high sensitivity to low soil moisture. The effects of acute and chronic desiccation on survival and reproduction were determined in Enchytraeus albidus and Enchytraeus crypticus. Further, effects of acute drought stress on the water balance physiology and accumulation of osmolytes were investigated in E. albidus. Survival of E. crypticus and E. albidus was significantly influenced by exposure time. Reproduction was much more sensitive to desiccation than survival and was significantly reduced from -0.06 bar, which was surprising because no dehydration or change in the body fluid osmolality of E. albidus occurred until much harsher drought regimes occurred. The body fluid osmolality of E. albidus was relatively high, about 500 mOsm. Congruent with this no water loss or changes in osmotic pressure occurred until equivalent or higher water potential values of the environment were reached. Two osmolytes, glucose and alanine, were up-regulated in drought exposed E. albidus. Even though enchytraeids display moderate physiological protection to rapid changes in soil moisture (by having a high osmotic pressure) in the short term, populations subjected to long-term drought stress can be severely reduced even under moderate drought levels.