Respiration rates of tropical Atlantic copepods in relation to the oxygen minimum zone

Zooplankton respiration plays an important role in the carbon cycling of pelagic ecosystems. The rate of oxygen consumption in zooplankton is affected by the physical environment, vertical distribution range and species-specific behavior. Especially in tropical oceans, oxygen minimum zones (OMZs) may influence zooplankton metabolic processes and vertical distribution and thus structure zooplankton communities. Here we present respiration rates of tropical Atlantic copepods in relation to environmental factors, especially O2 concentration, and species-specific characteristics. Copepods were sampled during two research stays on the Cape Verde Island São Vicente in March/April and May/June 2010. Minimum O2 concentrations of 51 μmol kg− 1 (pO2 of 4.25 kPa) at 400 m depth were recorded within the OMZ. Respiration rates of epi- and mesopelagic calanoid copepods were measured by optode respirometry at three different ambient temperatures (13, 18, and 23 °C) to establish the effect of temperature on metabolic rates. Mass-specific oxygen consumption ranged from 27 μmol O2 gDM− 1 h− 1 in copepodids C5 of Lophothrix sp. at 13 °C to 774 μmol O2 gDM− 1 h− 1 in Pleuromamma xiphias copepodids C5 at 18 °C and was mainly controlled by body mass and temperature. Mass-specific respiration rates were highest in surface-dwelling organisms and decreased with increasing depth. To allow for a comparison of shallow and deep-living copepods, respiration rates were standardized to a common temperature of 18 °C and a mean body dry mass of 0.5 mg, applying a Q10 of 2.0 and a body mass exponent of − 0.56. Temperature- and body mass-corrected respiration rates did not decrease with increasing depth indicating that neither depth of occurrence, nor current hypoxic conditions within the OMZ had a fundamental, persistent effect on zooplankton respiration.