Respiration, ETS activity and dissolved organic carbon excretion of tropical and subtropical zooplankton

Abstract

Respiration and electron transport system (ETS) activity were measured in mixed epipelagic copepods, diel vertical migrant copepods and euphausiids in order to estimate their role in the biological carbon pump. Experiments were performed in a transect along the tropical and subtropical Atlantic Ocean and around the Canary Islands. Respiration rates in both migrant copepods and euphausiids showed high values during the first 4 hours of incubation followed by a decrease until the end of the experiment. Conversely, respiration rates in epipelagic copepods increased during the same period, but not statistically significant. This variability found during the first hours of short-term experiments suggests that early hours of incubation should be considered in metabolic studies. Differences between organisms were also observed in ETS activity results. Migrant euphausiids showed rather constant ETS activity values while in both migrant and epipelagic copepods followed the same increasing trend as respiration rates of epipelagic copepods. The R/ETS ratio values obtained for migrant euphausiids were higher than expected, suggesting the need of more studies. An allometric relationship between respiration and ETS in relation to body mass was also found. Dissolved organic carbon (DOC) decreased with time of incubation, providing preliminary results about carbon excretion in migrant euphausiids. These results will be used to assess active flux due to diel vertical migrants in the ocean.