Benthic macroinfaunal community structure, resource utilisation and trophic relationships in two Canadian Arctic Archipelago polynyas

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 δ ) 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 δ 13 C 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.

Landfast sea ice-benthic coupling during spring and potential impacts of system changes on food web dynamics in Eclipse Sound, Canadian Arctic

“…Sea-ice extent and thickness are declining in the Arctic Ocean (Pizzolato et al 2014, Harada 2016 and in the Canadian Arctic (Environment andClimate Change Canada 2016, Stroeve &Notz 2018), causing alterations in timing, magnitude and spatial distribution of primary production in the sea ice and the water column (Ardyna et al 2014, Assmy et al 2017, Blais et al 2017. This yields profound implications for the dependent ice-associated, pelagic and benthic food webs in the Canadian Arctic (Hobson et al 2002, Roy et al 2015, Mäkelä et al 2017) and other Arctic near-shelf locations (McMahon et al 2006, Søreide et al 2013 as well oceanic regions (Kohlbach et al 2016(Kohlbach et al , 2017. Chan ges at the base of the food web will affect the energy flow from lower to higher trophic levels with un certain consequences for top predators (Hays et al 2005, Wassmann 2015.…”

Short-term processing of ice algal- and phytoplankton-derived carbon by Arctic benthic communities revealed through isotope labelling experiments

“…As our measurements were taken at a time when SCOC rates in NOW and LS are usually at their annual peak, it is possible that the effect of the algal addition was masked by the already high background SCOC. The sediment C:N ratio (6.5 at both sites) and organic matter (10−11%) and chl a (13−21 mg dry weight m −2 ) contents recorded at NOW and LS during sampling indeed suggest recent deposition of labile orga nic matter (Mäkelä et al 2017b). A similar dampening effect has also been suggested by Sun et al (2007), who observed algal addition to have no marked effect on SCOC in Smeerenburg Fjord, Svalbard, where the sediments had a high initial orga nic matter loading and surface sediment chl a content of < 2.5 µg g −1 dry sediment.…”

“…Bacterial uptake of C IA and C PP was also significant, with 33−44% of the total C processing directed towards bacterial assimilation and growth, which was also illustrated by the high bacterial growth efficiency and rapid increase in bacterial biomass after algal additions. Interestingly, despite the high macroinfaunal biomass and density at both LS and NOW (Mäkelä et al 2017b), the role of these fauna, mainly polychaetes and crustaceans in NOW and polychaetes and bivalves in LS, in the processing of C IA and C PP was negligible. However, the overall biological processing in neither LS nor NOW seems to correspond with the categories of labelled C processing patterns identified by Woulds et al (2009Woulds et al ( , 2016.…”

“…1, Table 1). The sites are known as hotspots for both Arctic marine PP (Klein et al 2002, Lalande et al 2009, Roy et al 2015 and benthic faunal diversity and biomass (Thomson 1982, Link et al 2013b, Mäkelä et al 2017b. The annual PP rates in LS (60 g C m −2 yr −1 ) and NOW (254 g C m −2 yr −1 ) (Welch et al 1992, Klein et al 2002 are dominated by phytoplankton, with 3 and 10% of PP attributed to ice algae in NOW and LS, respectively (Welch et al 1992, Michel et al 2002, Tremblay et al 2006.…”

“…However, as the temperature was the same for all incubation cores, it does not affect the experimental design and testing of the hypotheses themselves. It should also be noted that bacteria and macroinfauna have very limited mobility, and as ice algae often sink to the seafloor in patchy aggregations and not in an evenly distributed rain of cells like phytoplankton do, the smaller size classes of benthic consumers may not have similar access to ice algae as highly mobile consumers do (Iken et al 2001, MacDonald et al 2010, Mäkelä et al 2017b. This agrees with the observations by Boetius et al 2013, who showed that only mobile mega fauna and possibly bacteria used ice algal patches as a food source in the central Arctic Ocean.…”