Sea-ice properties and nutrient concentration as drivers of the taxonomic and trophic structure of high-Arctic protist and metazoan communities

Abstract

In the Arctic Ocean, sea-ice decline will significantly change the structure of biological communities. At the same time, changing nutrient dynamics can have similarly strong and potentially interacting effects. To investigate the response of the taxonomic and trophic structure of planktonic and ice-associated communities to varying sea-ice properties and nutrient concentrations, we analysed four different communities sampled in the Eurasian Basin in summer 2012: (1) protists and (2) metazoans from the under-ice habitat, and (3) protists and (4) metazoans from the epipelagic habitat. The taxonomic composition of protist communities was characterised with 18S meta-barcoding. The taxonomic composition of metazoan communities was determined based on morphology. The analysis of environmental parameters identified (i) a 'shelf-influenced' regime with melting sea ice, high-silicate concentrations and low NO x (nitrate + nitrite) concentrations; (ii) a 'Polar' regime with low silicate concentrations and low NO x concentrations; and (iii) an 'Atlantic' regime with low silicate concentrations and high NO x concentrations. Multivariate analyses of combined bio-environmental datasets showed that taxonomic community structure primarily responded to the variability of sea-ice properties and hydrography across all four communities. Trophic community structure, however, responded significantly to NO x concentrations. In three of the four communities, the most heterotrophic trophic group significantly dominated in the NO x-poor shelf-influenced and Polar regimes compared to the NO x-rich Atlantic regime. The more heterotrophic, NO x-poor regimes were associated with lower productivity and carbon export than the NO x-rich Atlantic regime. For modelling future Arctic ecosystems, it is important to consider that taxonomic diversity can respond to different drivers than trophic diversity.

Carbon Export in the Seasonal Sea Ice Zone North of Svalbard From Winter to Late Summer

“…Small heterotrophs were more prominent during the post-bloom period (Lavrentyev et al, 2019), which would likely increase recycling and remineralization in the upper water column, preventing organic matter from sinking out of the epipelagic zone (Olli et al, 2002) and allowing high POC standing stocks to remain suspended. These findings agree with previous observations and predictions for the future SIZ, where a longer ice-free period late in the summer would be characterized by regenerated production, where the quality of the exported material would be increasingly degraded and recycled (Wassmann and Reigstad, 2011;Flores et al, 2019).…”

Sea ice decline drives biogeographical shifts of key Calanus species in the central Arctic Ocean

“…The Arctic sea ice is becoming younger (Comiso, 2012) and thinner (Kwok et al, 2009), with more and more area becoming seasonally ice covered, leading to changes in the surface water properties and affecting surface circulation patterns (Polyakov et al, 2018, 2020). The importance of sea ice in the life cycles of zooplankters, including Calanus , has been well documented (Bluhm et al, 2011; Ehrlich et al, 2020; Flores et al, 2019; Runge & Ingram, 1991; Werner & Hirche, 2001), and it is fully expected that the aforementioned changes will be reflected in the communities and organisms living beneath the ice (Leu et al, 2011; Søreide et al, 2010).…”

Changes in Sea-Ice Protist Diversity With Declining Sea Ice in the Arctic Ocean From the 1980s to 2010s

“…During the melt season, ponds develop on top of the ice and increase light transmission from 5-15% below white ice to 40-70% below ponds (Ehn et al, 2011;Katlein et al, 2019). A continuation of the observed decline in sea-ice extent and thickness will increase the amount of light penetrating into the Arctic Ocean (Nicolaus et al, 2012), which will further enhance melting and alter the upper ocean ecosystem (Flores et al, 2019). In particular the snow thickness on top of the ice controls light penetration and, thus, the accumulation of ice algal biomass, with highest biomass under thin snow cover (Leu et al, 2015).…”