Influence of the late winter bloom on migrant zooplankton metabolism and its implications on export fluxes

Studies on carbon active fluxes due to diel migrants are scarce and critical for carbon flux models and biogeochemical estimates. We studied the temporal variability and vertical distribution of biomass, indices of feeding and respiration of the zooplanktonic community north off the Canary Islands during the end of the late winter bloom, in order to assess vertical carbon fluxes in this area. Biomass distribution during the day presented two dense layers of organisms at 0–200 m and around 500 m, whereas at night, most of the biomass concentrated in the epipelagic layer. The gut pigment flux (0.05–0.18 mgC·m− 2·d− 1) represented 0.22% of the estimated passive export flux (POC flux) while potential ingestion represented 3.91% of the POC (1.24–3.40 mgC·m− 2·d− 1). The active respiratory flux (0.50–1.36 mgC·m− 2·d− 1) was only 1.57% of the POC flux. The total carbon flux mediated by diel migrants (respiration plus potential ingestion) ranged between 3.37 and 9.22% of the POC flux; which is three-fold higher than calculating ingestion fluxes from gut pigments. Our results suggest that the fluxes by diel migrants play a small role in the downward flux of carbon in the open ocean during the post-bloom period.

► Diel migrant mediated active C fluxes were assessed in a mesoscale free area. ► This is a comparison point for further studies in Canary area. ► Active C fluxes estimated were 1 to 5-fold lower than in mesoscale influenced area. ► Productive pulse of the late winter bloom and dust storm events enhance the gut flux. ► Mesoscale variability, seasonality and migrants diet may alter subtropical ocean C-cycle.