Respiration in marine zooplankton-the other side of the coin: CO2 production

We measured respiratory release rates of CO, from various taxonomic groups of zooplankton during three cruises in winter, spring, and summer in the North Atlantic Ocean. Zooplankton species collected comprised different species of thaliacea (salps), mollusc thecosomes, amphipod hyperiids, copepods, decapods, and euphausiids. Hourly, individual rates ranged from a minimum of 0.02 mul h(-1) for the smallest copepods (Oncaea sp. and Acartia) to a maximum of 90.6 mul CO, for the largest euphausiids (Meganyctiphanes norvegica), corresponding to a range of weight-corrected rates of 0.1 mul CO2 for the thecosome Cymbulia peronii and 5.6 mul CO2 for the smallest copepods. Size was the major factor controlling the recorded rates. Allometric coefficients varied between 0.6 and 0.7 for weight and 1.5 and 2.2 for length, which is in agreement with the theoretical values and the values recorded for oxygen consumption. RQ values (CO2 released/O-2, consumed) were computed for each group from simultaneous measurements of both respiratory processes. Model 11 regressions yielded mean RQs of 0.87 +/- 0.40 for copepods, 0.94 +/- 0.40 for thecosomes, and 1.35 +/- 0.08 for large crustacean and salp species. We propose that the increase in RQ value from copepod to large crustacean species is related to the development of the muscular mass and activity rather than a simple shift in respiratory metabolic substrate. Realistic RQ values, taking species differences into account, should be used to derive population and community CO2 release rates from simpler oxygen consumption measurements.