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Stief P, Lundgaard ASB, Nielsen TG, Glud RN
Feeding-related controls on microbial nitrogen cycling associated with the Arctic marine copepod Calanus hyperboreus
The concept of pelagic microsites that host anaerobic microbial activities has increasingly become recognised in aquatic biogeochemistry. Millimeter-size aggregates with an oxygen-deficient interior enable biogeochemical processes, such as fixed-nitrogen loss through denitrification, that would otherwise not occur in the oxygenated water column. Stief and coworkers show that the Arctic copepod Calanus hyperboreus and its fecal pellets and carcasses represent such pelagic microbial hotspots. Live specimens with a filled (anoxic) gut exhibited high denitrification activities, which were partially retained in fecal pellets and carcasses for several days of simulated sinking through the water column. It is estimated that during the Arctic spring bloom, the pelagic fixed-nitrogen loss associated with calanoid copepods is equivalent to 28% of the benthic fixed-nitrogen loss.