Influence of body mass, food concentration, temperature and filtering activity on the oxygen uptake of the appendicularian Oikopleura dioica

In appendicularians, filtering activity is known to vary inversely with food concentra- tion. Here, we investigate the response of respiration rate to clearance rate (notably tail beating), which is minimum in anesthetized animals and maximum in conditions of food deprivation. Respira- tion of different size classes of the appendicularian Oikopleura dioica was measured at 15°C in 4 con- trasting situations: in (1) high (H) and (2) low (L) concentrations of a lyophilized mixture of Isochrysis galbana (haptophyceae), with Thalassiosira pseudonana (diatom) offered as food, (3) without food and (4) in the presence of an anaesthetic. Measurements of the oxygen consumption in H concentra- tion were repeated at 22°C to examine the effect of temperature on respiration. The weight-specific respiration measured in H, L, and no food conditions were not significantly different. The absence of an apparent relationship between the activities of filtration and respiration may be explained by the unusual high basal oxygen consumption measured in anaesthetized appendicularians (67% of the total respiration rate of active animals). Our results also suggest that the respiration rate of O. dioica was overestimated in past studies (1.6 to 2.0 times). Despite this, the respiration of O. dioica measured in this study is generally higher than the rates reported for other zooplankton species. The Q10 de- termined from the temperature-dependent oxygen consumption (2.3) was close to the earlier obser- vations.