Models of Plankton Community Changes during a Warm Water Anomaly in Arctic Waters Show Altered Trophic Pathways with Minimal Changes in Carbon Export

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.

Food Web Functions and Interactions During Spring and Summer in the Arctic Water Inflow Region: Investigated Through Inverse Modeling

“…The microzooplankton diet changed predominantly to detritus (27-43% of food intake), with carnivory (4-15%) and bacterivory (7-18%) of lower importance in August. The available evidence thus supports a flexible omnivorous feeding behavior of the dominant zooplankton groups, which is in line with recent studies from the Arctic (Forest et al, 2011;Vernet et al, 2017).…”

“…Further, the long-term environmental monitoring revealed a 1 • C higher warm water anomaly event in the Atlantic Water inflow from 2005 to 2007, accompanied with shifts in dominant phytoplankton species in summer from large-celled diatoms to smaller flagellates like coccolithophorides and Phaeocystis, a change which appeared persistent also after the reversal of the temperature anomaly (Nöthig et al, 2015). These changes at the primary producers level cascaded further into the food web, where mesozooplankton adapted by shifting from predominantly herbivory to omnivory and detritivory (Vernet et al, 2017).…”

“…It enables estimating elemental budgets and reconstructing otherwise notoriously difficult to measure trophic flows between living compartments, using the relatively easy to measure biomasses of these compartments; a set of measured flows (e.g., primary production and respiration), food web topology, and biologically meaningful constraints on the trophic flows (De Laender et al, 2010). The methodology has been used to quantify planktonic food web flows in natural and experimental systems (Vézina et al, 2000;Olsen et al, 2006;Luong et al, 2014), has been used to track biogenic carbon flow in the Arctic (Vézina et al, 2000;Forest et al, 2011;Vernet et al, 2017), and last but not least, is coded in open source software (LIM library of the R software) with good explanatory texts (Soetaert and van Oevelen, 2009;van Oevelen et al, 2010).…”

Arctic marine fungi: biomass, functional genes, and putative ecological roles

“…DNA was then purified using DNeasy PowerSoil Kit (Qiagen, Hilden, Germany) collection tubes and wash buffers, following the manufacturer's suggested protocol. For 18S rRNA gene sequencing analysis, target amplicons were generated by PCR (30 cycles) using the Earth Microbiome Project primers: Euk1391f: (5′-GTACACACCGCCCGTC-3′) and EukBr: (5′-TGATCCTTCTGCAGGTTCACCTAC-3′) (28) to generate ∼170 base pair reads specific to the V9 hypervariable region. PCR products were generated using fusion primers with the Fluidigm CS1 or CS2 universal oligomers added to 5' ends.…”

“…The use of ergosterol as a fungal biomarker is not suitable for the Chytridiomycota, as they do not synthesize ergosterol (27). Understanding the ecology and biomass contributions of the fungi is important for integrating fungal contributions into food web analyses and informing ecosystem modeling efforts (28).…”