Temperature-dependent energy budget of an Arctic Cladoceran, Daphnia middendorffiana

1. Global change models predict the greatest impact in climate to occur in the northern polar region. Change in temperature will alter individual metabolism and has the potential to change community structure to an unknown degree. 2. The temperature-dependent energy budget of Arctic Daphnia middendorffiana was investigated by measuring respiration rates, ingestion rates and assimilation rates. The scope for growth and reproduction was determined and compared with data from the literature for a clone of Daphnia pulicaria collected in the temperate zone. 3. A difference was observed between the Arctic species and the temperate zone clone in both temperature tolerance, and the energy available for growth and reproduction at various temperatures. A low availability of energy for growth and reproduction indicated that life history patterns as well as physiological mechanisms are important in allowing D. middendorffiana to exist successfully in Arctic environments. 4. The lower available energy for growth compared to Daphnia clones from temperate zones may be detrimental to D. middendorffiana, which might have to compete with species expanding their range under the predicted temperature increase for Arctic regions.