Salinity modulates the temperature-induced increase in oxygen consumption in the temporary-pond ostracod Cypris bispinosa (Crustacea: Ostracoda)

Despite the ecological relevance of podocopid ostracods as paleo- and bioindicators, the combined effects of temperature and salinity on their respiratory physiology have rarely been investigated. New experimental evidence is presented here on the drivers of oxygen consumption in Cypris bispinosa , a common inhabitant of temporary ponds and one of the largest freshwater ostracods in Europe. Closed-cell respirometry measurements were conducted over five experimental runs performed at different salinities (0.03, 0.3, 1, 3, and 6 PSU). Within each experimental run, five replicate groups, each consisting of five adult Cypris bispinosa , were exposed to a sequential, stepwise temperature increase (5 → 10 → 15 → 20 → 25°C). In addition, by compiling occurrence records and associated environmental data, we characterised the conditions under which the species typically occurs, which allows the experimental results to be interpreted within its natural ecological context. As expected, oxygen consumption rates were higher as temperature increased, but there were some significant interactions between salinity and temperature treatments. The highest median OCR value (3.0 μ l O 2 /h per mg) was observed at 25°C and at 1 PSU, a salinity close to those most frequently occupied by the species in nature (0.65 PSU), suggesting that salinity may constrain the capacity of wild individuals to adjust oxygen uptake under warming conditions. These findings expand the still limited physiological information available for freshwater podocopid ostracods and provide a basis for further investigation of their responses to interacting environmental stressors.