Comparison of respiration rate and electron transport system (ETS) enzyme-mediated reduction assay of the invasive copepod Eurytemora carolleeae Alekseev & Souissi, 2011 (Calanoida, Temoridae) in Green Bay, WI, U.S.A.
Anthropogenic activities can cause important changes in aquatic ecosystems, such as warming due to climate change, nutrient loading from agricultural runoff and urban areas, and decreased concentrations of oxygen in bottom waters. These changes may lead to impacts on both organism performance and ecosystem functionality. Studying planktonic species that form an aquatic ecosystem's foundation is an important step towards understanding the entire food web and predicting how it may respond to a changing environment. One important planktonic species in the Laurentian Great Lakes is the invasive calanoid copepod Eurytemora carolleeae (formerly considered part of the Eurytemora affinis species complex). This study analyzes the metabolic activity of E. carolleeae from Green Bay, Lake Michigan, U.S.A. using two different methods, over a range of temperatures from 9 to 26°C. Total oxygen consumption was measured directly using a micropulse oxygen probe system, and the activity of aerobic metabolic enzymes in the electron transport system (ETS) was quantified using in vitro reduction of iodonitrotetrazolium chloride (INT). Respiration rate of E. carolleeae increases approximately linearly from 9 to 26°C. Measurements of ETS activity indicate that the copepod's metabolic enzymes have an Arrhenius activation energy of 46.5 ± 15.6 kJ/mol with a thermal maximum between 22 and 26°C. Overall, E. carolleeae ETS rates increased by approximately 7% per °C over the range 9 to 22°C. This thermal limit has implications for future performance of this species, as the combination of higher temperatures and disappearance of oxygenated colder-water refuges may limit E. carolleeae's success in the Green Bay system following warmer climate and increased nutrient conditions.