Seasonal change in acclimatised respiration rate of Temora longicornis

We investigated the seasonal changes in the respiration rate (R) of adult Temora longicornis (Müller) acclimatised to in situ conditions over 1 yr. Mean (±1 SE) R varied from 50.5 ± 2.8 nl O2 ind.-1 h-1 in December to 73.2 ± 3.53 nl O2 ind.-1 h-1 in August for copepods of mean body dry weight (DW) of 33.5 ± 1.1 and 26.3 ± 0.95 µg, respectively. Males represented ~8% of the total measurements, and their respiration did not differ significantly from that of females. R scaled isometrically with dry weight (DW), i.e. the allometric exponent of the power function (R = aDWb) did not differ significantly from unity (b = 0.83 to 1.35). The relationship between in situ weight-specific respiration rate (Rsp) and temperature (T) was described by a sigmoid trend with Q10 ranging from 1 to 2.88 (mean 1.57 to 1.89). In contrast, the acclimated and acutely measured Rsp of copepods maintained under optimal feeding conditions in the laboratory increased exponentially with temperature and were characterised by higher mean Q10 of 2.05 and 2.41, respectively. Acclimatised ln R increased significantly with ln DW, T, ln chlorophyll a (ln Chl) and ln egg production rate (ln EPR). Our results indicate that seasonal changes in T. longicornis respiration rate are not simply determined by body mass and temperature but also reflect copepod nutritional and reproductive condition. We argue that predictive ecological models using fixed thermal coefficient values may overestimate copepod respiration, particularly under ambient conditions limiting growth and reproduction. Our findings have important implications for the calculation of carbon flow in marine food-webs and for understanding how zooplankton physiology responds to changes in global temperature