Effects of single and dual-stressor elevation of environmental temperature and P-CO2 on metabolism and acid-base regulation in the Louisiana red swamp crayfish, Procambarus clarkii

Elevation of temperature and CO2 levels within the world's aquatic environments is expected to cause numerous physiological challenges to their inhabitants. While effects on marine ecosystems have been well studied, freshwater ecosystems have rarely been examined using a dual-stressor approach leaving our understanding of its inhabitants upon these challenges unclear. We aimed to identify the affects of elevated temperature and hypercapnia in isolation and in combination on the metabolic and acid-base regulatory processes of a freshwater crayfish, Procambarus clarkii. Crayfish were exposed to freshwater conditions that may be prevalent by the year 2100 and metabolic responses were determined after 14-days of exposure. In addition, changes in branchial mRNA expression of acid-base linked transporters were investigated. Interactions between exposure conditions influenced extracellular pH as well as the nitrogen physiology and routine metabolic rate of the crayfish. Crayfish exposed to individual and combined elevations in temperature and/or hypercapnia maintained an extracellular pH similar to that of control crayfish. Dual-stressor exposed crayfish seem to elevate the importance of ammonium as an excretable acid-equivalent based on an overall increase in the branchial mRNA expression of transporters related to ammonia excretion including the Na+/K+-ATPase, Rhesus-protein, and the V-type H+- ATPase. Overall, hypercapnia and dual-stressor conditions caused a metabolic depression that may have longlasting consequences such as limited locomotion, growth, and reproduction. Future generations of crayfish given the chance to adapt over several generations may ameliorate these consequences.