Abstract
Carbon flow through pelagic food webs is an expression of the composition, biomass and activity of phytoplankton as primary producers. In the near future, severe environmental changes in the Arctic Ocean are expected to lead to modifications of phytoplankton communities. Here, we used a combination of linear inverse modeling and ecological network analysis to study changes in food webs before, during, and after an anomalous warm water event in the eastern Fram Strait of the West Spitsbergen Current (WSC) that resulted in a shift from diatoms to flagellates during the summer (June–July). The model predicts substantial differences in the pathways of carbon flow in diatom- vs. Phaeocystis/nanoflagellate-dominated phytoplankton communities, but relatively small differences in carbon export. The model suggests a change in the zooplankton community and activity through increasing microzooplankton abundance and the switching of meso- and macrozooplankton feeding from strict herbivory to omnivory, detritivory and coprophagy. When small cells and flagellates dominated, the phytoplankton carbon pathway through the food web was longer and the microbial loop more active. Furthermore, one step was added in the flow from phytoplankton to mesozooplankton, and phytoplankton carbon to higher trophic levels is available via detritus or microzooplankton. Model results highlight how specific changes in phytoplankton community composition, as expected in a climate change scenario, do not necessarily lead to a reduction in carbon export.
Highlights
The Arctic Ocean is one region where climate change is most pronounced, impacting the pelagic environment with observed effects on stratification, pH and currents
At the time of the warm water pulse, higher phytoplankton biomass was observed in the water column, protistan plankton >3 μm changed in composition, and diatoms that dominated the period before the warm event switched to a dominance by coccolithophores in 2004, followed by Phaeocystis pouchetii dominance in 2006 (Nöthig et al, 2015)
Carbon flow through pelagic food webs is impacted by the composition and biomass of the primary producers, the phytoplankton
Summary
The Arctic Ocean is one region where climate change is most pronounced, impacting the pelagic environment with observed effects on stratification, pH and currents. The consequences of these effects on phytoplankton are complex. Large zooplankton (e.g., Calanus spp.) feeding on the phytoplankton spring bloom, usually dominated by large cells, is known to produce a pulse of sedimentation through fecal pellet formation (Forest et al, 2010) Within this paradigm, it is expected that an absence of large cells, i.e., diatoms, will decrease the flux of material to the sediments (Wohlers et al, 2009)
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