Copepod summer grazing and fecal pellet production along the Western Antarctic Peninsula

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Copepods are important grazers on phytoplankton and contributors to carbon export, but their role is poorly understood in the Western Antarctic Peninsula (WAP), a region of high productivity and rapid climate warming. We conducted grazing and egestion experiments with large, dominant copepods each January from 2012 to 2014. We found higher gut evacuation rates (k), initial gut pigment and ingestion rates (I) for Calanus propinquus and Rhincalanus gigas compared with Calanoides acutus. Since k and I linearly increased with chlorophyll a for most species, ingestion rates were 4-70 times greater in more productive coastal regions than offshore, slope waters. Copepods have a low grazing impact on phytoplankton biomass (<1%) and productivity (1%, up to 11%) compared with the dominant WAP macro- and microzooplankton. Egestion rates were high (0.8-37.3 μgC ind.−1 day−1); however, ∼58% of fecal pellets are retained in the upper water column. Daily carbon rations of ∼1% indicated feeding on other carbon sources (protozoans and metazoans) to meet metabolic demands. However, during a coastal phytoplankton bloom, daily C rations increased to up to 13%, indicating increased reliance on phytoplankton. Future changes in the WAP plankton community may affect food web carbon flow and export.

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