Abstract
Climate change driven alterations to patterns of Arctic marine primary production, with increasing phytoplankton- and decreasing ice algal production, have the potential to change the resource utilisation and trophic structure of the benthic communities relying on the algae for food. To predict the benthic responses to dietary changes, we studied the macroinfaunal community compositions, and used the faunal δ13C and δ15N signatures to investigate their main food sources and trophic positions in North Water (NOW) and Lancaster Sound (LS) polynyas in the Canadian Arctic Archipelago. Macroinfaunal density (10 952 ind. m-2) and biomass (3190 mg C m-2) recorded in NOW were higher than previously found in the Arctic at depths >500m, and significantly higher than in LS (8355 ind. m-2 and 2110 mg C m-2). This was attributed to higher particulate organic matter fluxes to seafloor in NOW. Polychaetes were significant taxa at both sites in terms of density and biomass, and in addition crustacean density in NOW and bivalve density in LS were high. Facultative filter and surface deposit feeders were highly prevalent at both sites, suggesting feeding plasticity is a successful strategy for accessing different food sources. The macrofaunal δ13C signatures reflected the signatures of pelagic particulate organic matter at the sites, and an isotope mixing model confirmed phytoplankton as the main food source for most taxa and feeding guilds. The food web length in LS was longer than in NOW (3.2 vs. 2.8 trophic levels). This was attributed to a larger reliance on reworked organic matter by the benthic community in LS, whereas the high export fluxes at the highly productive NOW resulted in higher rates of selective consumption of fresh algal matter. Despite studies suggesting that loss of ice algae from consumer diets in the Arctic might have a negative impact on the benthos, this study suggests that Arctic macrobenthic communities thrive using phytoplankton as their main food source and should thus be able to cope or even benefit from predicted changes to patterns of primary production.
Highlights
Climate change is drastically altering the Arctic marine ecosystem, and sea ice cover, the most conspicuous feature of the Arctic Ocean, is being reduced at a rate that could leave the region free of summer sea ice by 2040 [1]
The C biomass at the (Table 2) site was found to be significantly higher than the Lancaster Sound (LS) biomass (Independent samples t-test, t = 2.746, df = 26.168, p = 0.011)
This study shows that both North Water Polynya and Lancaster Sound Polynya are among the most significant benthic macroinfaunal hotspots in the Arctic Ocean, where the macrofaunal communities thrive on a diet consisting mainly of phytoplankton food, opportunistically supplemented with ice algae
Summary
Climate change is drastically altering the Arctic marine ecosystem, and sea ice cover, the most conspicuous feature of the Arctic Ocean, is being reduced at a rate that could leave the region free of summer sea ice by 2040 [1]. The export of particulate organic matter (POM) to the seafloor is higher in these hotspots compared to less productive Arctic waters [17,18], especially during the early spring when zooplankton grazing and growth is limited [19,20] This tight benthic-pelagic coupling is generally reflected in the high benthic community biomass at these sites [21,22,23,24,25], increased water depth weakens the relationship [26]. Even in North Water Polynya (), one of the most well-studied and most biologically productive ecosystems in the Arctic [31,32], data on benthic macroinfauna is limited in taxonomic detail or spatial extent [24,33,34,35] This lack of baseline data makes it difficult to monitor the influence of climate change on the benthic communities as a whole
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