Copepod community ingestion and respiration in the Eastern Atlantic Ocean during POLARSTERN cruise PS81 (ANT-XXIX/1)

The copepods' impact on vertical carbon flux was assessed for stratified depth layers down to 2000 m at six stations along a transect between 24°N and 21°S in the eastern Atlantic Ocean in October/November 2012. Total copepod community consumption ranged from 202-604 mg C m⁻² day⁻¹, with highest ingestion rates in the tropical North Atlantic. Calanoids consumed 75-90% of the particulate organic carbon (POC) ingested by copepods, although the relative contribution of cyclopoids (mostly Oncaeidae) increased with depth. Net ingestion (=consumption - fecal pellet egestion) of POC varied from 106-379 mg C m⁻² day⁻¹ for calanoids and 37-51 mg C m⁻² day⁻¹ for cyclopoids, corresponding to 16-58% and 5-9%, respectively, of primary production (PP). In total, 9-33% and 2-5% of PP were respired as inorganic carbon by calanoids and cyclopoids, respectively. Copepod ingestion was highly variable between stations and depth layers, especially in the epi- and upper mesopelagic zone. Diel vertical migrants such as Pleuromamma enhanced the vertical flux to deeper layers, particularly in the region influenced by the Benguela Current. The impact of copepod communities on POC flux decreased below 1000 m and POC resources reaching the bathypelagic zone were far from being fully exploited by copepods. As key components, copepods are important mediators of carbon fluxes in the ocean. Their biomass, community composition and interactions strongly affect the magnitude of organic carbon recycled or exported to deeper layers. High variability, even at smaller vertical scales, emphasizes the complex dynamics of the biological carbon pump.