The missing piece of the upper mesopelagic carbon budget? Biomass, vertical distribution and feeding of aggregate-associated copepods at the PAP site

•Aggregate-associated copepods can have a large influence on the attenuation of the vertical flux.•Particle degradation by these copepods can equal the surplus in the epipelagic carbon.•Biomass of M. norvegica and Oncaea spp. is variable both in time and in space.•Understanding their distribution is needed to predict the changes in the biological pump. Although zooplankton are recognized as important consumers of marine snow, our knowledge of the contribution of the small ( 2-fold between sampling dates for geographically-close sampling stations. Microsetella norvegica resided mainly in the surface layer, at or immediately below the fluorescence peak, while Oncaea spp. was typically deeper. Microsetella norvegica fed actively on Trichodesmium filaments, with a maximum ingestion rate of ca. 0.11 µg C ind.−1 d−1, while their ingestion of detritus aggregates was low. Feeding on Trichodesmium was reflected in their gut chl-a content, which was high for M. norvegica at all but one sampling time. In contrast, Oncaea spp. had significantly lower gut chl-a content and may have been feeding on other types of aggregates. Respiration of both copepods was variable and as much as 0.08 µL ind.−1 h−1 for M. norvegica and 0.04 µL ind.−1 h−1 for Oncaea spp. Based on individual biomass, vertical distribution, and carbon demand, aggregate-associated copepods could degrade up to 79 ± 33 mg C m−2 d−1, a value similar to the surplus in the epipelagic carbon budget of the area. This large degradation rate demonstrates that zooplankton