Synthesis toward a global model of metabolism and chemical composition of medusae and ctenophores

• Literature data of a total of 28–72 species of medusae and ctenophores were compiled.
• Body mass and habitat temperature but depth are predictors of their metabolic rates.
• They respire at higher rates than other zooplankton taxa of equivalent body N.
• Their C and N compositions decreased with increasing body mass and temperature.
• Body C:N ratios are stable, and suggest protein to be the major organic component.

Respiration and ammonia excretion data and chemical composition data [water content, ash, carbon (C), nitrogen (N) and C:N ratios] of a total of 28–72 species of hydromedusae, scyphomedusae, siphonophores and ctenophores from various depths of the world's oceans were compiled. Multiple regression analyses revealed that body mass and habitat temperature but habitat depth were significant predictors for respiration and ammonia excretion rates. The scale exponents of body mass (0.66–1.05) and temperature coefficients (1.7–3.1 as Q10) of the empirical regression models varied greatly by the choice of body mass units (DM, C or N). The O:N ratios (median: 15.0) were independent of these parameters. Body C and N compositions (% of DM) decreased with the increase in either DM or habitat temperature, showing a stable C:N ratio of 3.8 (by mass). Comparison of the present results with global-bathymetric features of chaetognaths, copepods, euphausiids and mysids revealed that the medusae and ctenophores are unique in that they maintain high metabolic rates per unit body N, lack significant effects of habitat depth on metabolic rates, have high specific growth rates, and have little accumulation of energy reserves (lipids) in the body.