Crayfish are major detritivores in stream communities and are important in recycling nutrients. Some have proposed their role as keystone species in the systems they inhabit, regulating plant detritus biomass and providing food for top predators. Therefore, any modification of feeding behavior or consumption of biomass by these animals will have major impacts at multiple levels of the ecosystem, including a decrease in detritus breakdown, less movement of carbon through aquatic systems, and removing the link between the detritivore and consumer food webs. The feeding behavior of crayfish is primarily mediated through chemoreception. Crayfish use chemical signals emanating from possible food items to forage efficiently. Organic compounds in food items, such as small ions or molecules, amino acids, nucleotides, or small peptides, play a large role in foraging and consumption decisions. The ratio at which chemicals are presented in food plays an important role in behavioral decisions. Therefore, changes in the chemical composition of a food source or in the ability of crayfish to detect food sources will lead to changes in the foraging behavior of a crayfish. Because of the central role that crayfish play in cycling carbon and structuring communities, any change in the foraging decisions of crayfish can have profound consequences on the trophic dynamics of aquatic systems. At UMBS, researchers have observed differential effects on nutrient quality and C:N ratios of leaves grown under high CO2 levels. In summary, although the leaves have grown faster, they have an altered C:N ratio. These changes in the chemical composition of the leaves should ultimately lead to a difference in how crayfish will perceive them. Because crayfish feed primarily on terrestrial detritus, the altered nutrient composition of leaves grown at elevated CO2 should decrease the growth rate and reduce the overall biomass of crayfish in the system. Thus, CO2 increases in the atmosphere may also have an impact on the aquatic detritivore food web through changes in behavior (due to changes in food preference) or differences in biomass (through changes in growth rate). This research will focus on how climate change, mainly elevated CO2, temperature, and reduced pH, affects both the food selection and growth rate of crayfish, Orconectes virilis. This experiment involves two parts: 1) to determine how foraging preferences of crayfish are altered by high CO2 leaves (obtained from the elevated CO2 experiments at UMBS), elevated temperatures and lowered pH in a simulated natural environment, and 2) growth of juvenile crayfish are altered under these same conditions.