Metabolic rates and carbon budget of early developmental stages of the marine cyclopoid copepod Oithona davisae

The genus Oithona has been considered the most abundant and ubiquitous copepod in the world's oceans. However, despite its importance, the metabolism of its developmental stages (nauplii and copepodites), crucial to explain their evolutionary success, is almost unknown. We determined respiration rates, ammonium and phosphate excretion rates, and the net growth efficiencies of early developmental stages of Oithona davisae as related to stage, body weight, temperature, and food availability. Respiration and excretion rates increased with increasing body weight and were positively related to temperature and food. Specific respiration rates of nauplii and copepodites varied from 0.11 to 0.55 d(-1) depending on stage, body weight, temperature, and food availability. Metabolic C:N ratios were higher than 14, indicating lipid-oriented metabolism. Assimilation efficiencies and net growth efficiencies ranged from 65% to 86% and from 23% to 32%, respectively, depending on body weight, stage, and temperature. Assimilation efficiencies and net growth efficiencies estimated using the respiration rates of nauplii with food were 1.7 times higher and 0.6 times lower, respectively, than those calculated using respiration rates of nauplii without food. Therefore, the use of respiration rates measured in filtered seawater led to substantial bias on the estimations of zooplankton carbon budget. O. davisae developmental stages exhibited similar assimilation and growth efficiencies but lower carbon-specific respiratory losses than calanoid copepods. Hence, the low metabolic costs of Oithona compared with calanoids may be one reason for their success in marine ecosystems.