Carbon flux in a subarctic Norwegian fjord: the potential seasonal impact of the small copepod, Microsetella norvegica

Benjamin Paul Mooney

The fate of primary production in the ocean has large implications on marine ecosystems. A small fraction of this production reaches the ocean floor as marine snow, where it might be sequestered. The rest is grazed and recycled within the pelagos by microbes and zooplankton. The contribution of each group to the degradation of organic carbon is uncertain, but direct observations of small copepods and organic aggregates suggests their role is more important than previously thought. The main aims of this study were to investigate the depth distribution and abundance of Microsetella norvegica, a small harpacticoid copepod, against vertical profiles of marine snow and fluorescence. Additionally, I estimated the amount of organic carbon consumed from sinking aggregates by M. norvegica. Samples were taken in the innermost part of Porsanger fjord using a video plankton recorder during four sampling periods throughout 2013 and 2014. M. norvegica was found in association with phytoplankton during bloom periods, but not in the winter. During non-bloom periods, M. norvegica followed a similar depth distribution to marine snow particles. M. norvegica explained 46.9 and 13.5% of the total carbon flux attenuation during October and November, respectively. These results suggest that small copepods that feed on marine snow particles have high-ecological impact in high latitude ecosystems, and are key organisms in carbon flux attenuation.