© 2016 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/fal/2016/0864 1863 - 9135/16/0864 $ 2.50 Bioenergetic cost of living in polluted freshwater bodies: respiration rates of the cyclopoid Eucyclops serrulatus under ammonia-N exposures Tiziana Di Lorenzo 1, *, Stefano Cannicci 2, 3 , Daniele Spigoli 3 , Marco Cifoni 1, 4 , Mariella Baratti 1 and Diana M. P. Galassi 4 With 2 figures and 3 tables Abstract: Ammonia-N (NH 3 +NH 4 + ) is considered one of the most important pollutants of freshwater bodies worldwide due to its high toxicity and ubiquity in freshwater ecosystems. The aim of this study was to assess if short-term exposures to sublethal ammonia-N concentrations affect the metabolic rates of the cyclopoid Eucyclops serrulatus. This is a target species for routine biomonitoring due to its world-wide distribution, wide ecological niche, short life-cycle and suitability to be easily reared in the laboratory. We measured the oxygen consumption as a proxy of possible metabolic reaction to stress under a 3-day exposure to two different ammonia-N concentra- tions, dosed as NH 4 + , at 15 °C. We also measured the respiration rates of juveniles (C1-C5 copepodids) separately from those of adults in order to assess whether the metabolic cost differed between the two stages. The respiration rates of both adults and copepodids increased with increasing NH 4 + concentrations. However, the adults of E. ser- rulatus experienced a significant energetic stress under exposure to 12 mg L –1 NH 4 + . On the contrary, the copepodid respiration rates significantly varied under exposure to 1 mg L –1 NH 4 + , just one order of magnitude greater than the current European threshold value for freshwater bodies. According to these outcomes, it is prudent to consider river monitoring sites not contaminated by ammonia-N under the current legislation to represent a risk for the juveniles of this species. Key words: ammonia-N; freshwater; copepod; oxygen; metabolism; respirometric Fundam. Appl. Limnol. Vol. 188/2 (2016), 147–156 Article published online 20 May 2016, published in print July 2016 Introduction Ammonia-N (NH 3 +NH 4 + ; Camargo & Alonso 2006) is considered one of the most important pollutants of freshwater bodies worldwide due to its high toxic- ity and ubiquity in freshwater ecosystems (U.S. EPA 2013). It occurs in very small amounts in pristine fresh- water bodies, as a result of the microbial reduction of nitrogen-containing compounds (EPA 2001). A sew- age or agricultural contamination is indicated when- ever ammonia-N concentrations exceed 0.129 mg L –1 NH 4 + in freshwater (EPA 2001). Although the average ammonia-N concentration in freshwater bodies has been decreasing in Europe since 1998, thus reflecting to some extent the effectiveness of the European Di- rectives, it still remains higher than the natural level Authors’ addresses: 1 Institute of Ecosystem Study – CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Florence, Italy 2 The Swire Institute of Marine Science and The School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong 3 Department of Biology, University of Florence, Via Madonna del Piano 6, 50019 Sesto Fiorentino, Florence, Italy 4 Department of Life, Health and Environmental Sciences, University of L’Aquila, Via Vetoio, 67100 Coppito, L’Aquila, Italy * Corresponding author: tiziana.dilorenzo@ise.cnr.it E