Biomarkers in Ringed Seals Reveal Recent Onset of Borealization in the High- Compared to the Mid-Latitude Canadian Arctic

Abstract

Warming of the Arctic has resulted in environmental and ecological changes, termed borealization, leading to the northward shift of temperate species. Borealization has occurred across all trophic levels, altering the structure of the food web. The onset and rate of borealization likely varies with latitude, depending on local warming and advection of warmer water into the Arctic. In order to assess latitudinal trends in food web structure in the Arctic, we analyzed stable nitrogen isotopes of specific amino acids alongside bulk stable carbon isotopes in ringed seal muscle tissue from the Canadian Arctic Archipelago (high-Arctic) and Southern Baffin Bay (mid-Arctic) from 1990 to 2016. Our results indicate a shift in food web structure in the high-Arctic that has occurred more recently when compared with the mid-Arctic. Specifically, over the past 25 years, the trophic position of ringed seals from the mid-Arctic was largely constant, whereas the trophic position of ringed seals decreased in the high-Arctic, reaching similar values observed in the mid-Arctic in 2015–2016. This suggests a potential shortening of the food chain length in the high-Arctic, possibly driven by changes in zooplankton communities feeding complexity in association with sea ice decline. This study identifies a temporal offset in the timing of borealization in the Canadian Arctic, resulting in different response of food webs to ecological changes, depending on latitude.

Multi‐decadal trends in biomarkers in harp seal teeth from the North Atlantic reveal the influence of prey availability on seal trophic position

“…Like Greenland Sea harp seals, harp seals from the Northwest Atlantic therefore integrate a δ 15 N baseline influenced by both 15 N‐enriched Pacific water and 15 N‐depleted Atlantic water over the year. de la Vega et al (2021) observed an increasing decadal trend in δ 15 N Phe in ringed seals from the Canadian Arctic Archipelago and Baffin Bay, that has been explained by the increasing influence of 15 N‐enriched Pacific‐derived water in these regions, and the effect of increasing primary production and in turn benthic denitrification. The increasing trend in δ 15 N Phe in ringed seals from the Baffin Bay was less pronounced than in the Canadian Arctic Archipelago, likely reflecting a dilution effect of the Pacific water influence when reaching southern Baffin Bay (de la Vega et al, 2021).…”

“…de la Vega et al (2021) observed an increasing decadal trend in δ 15 N Phe in ringed seals from the Canadian Arctic Archipelago and Baffin Bay, that has been explained by the increasing influence of 15 N‐enriched Pacific‐derived water in these regions, and the effect of increasing primary production and in turn benthic denitrification. The increasing trend in δ 15 N Phe in ringed seals from the Baffin Bay was less pronounced than in the Canadian Arctic Archipelago, likely reflecting a dilution effect of the Pacific water influence when reaching southern Baffin Bay (de la Vega et al, 2021). Here, the absence of trend in δ 15 N Phe in harp seals from the Northwest Atlantic population could result from the increased influence of both 15 N‐enriched Pacific water and 15 N‐depleted Atlantic water, counterbalancing each other in the migration area of this population.…”

Insights on long-term ecosystem changes from stable isotopes in historical squid beaks

“…These environmental effects lead to changes in the ecosystems, which mainly include increased generalization of the food webs, higher primary production, and inflow of boreal species into the Arctic marine ecosystems [ 3 – 5 , 7 – 11 , 16 , 18 , 19 ]. The retrospective SIA studies from the Arctic and North Atlantic to date use basal (= filter feeders) and top (= marine mammal top predators) food web components [ 21 , 22 , 31 , 32 , 34 – 41 , 43 , 44 ]. Shifts in their trophic ecology, which would coincide in time with the mentioned increased environmental impact of climate change since the late 1990s/early 2000s, were only evident in narwhals and ringed seals from East and West Greenland [ 21 , 22 , 31 , 32 , 34 – 41 , 43 , 44 ].…”

“…The retrospective SIA studies from the Arctic and North Atlantic to date use basal (= filter feeders) and top (= marine mammal top predators) food web components [ 21 , 22 , 31 , 32 , 34 – 41 , 43 , 44 ]. Shifts in their trophic ecology, which would coincide in time with the mentioned increased environmental impact of climate change since the late 1990s/early 2000s, were only evident in narwhals and ringed seals from East and West Greenland [ 21 , 22 , 31 , 32 , 34 – 41 , 43 , 44 ]. Ontogenetic changes and different timing of temporal changes in trophic ecology, however, were often found [ 21 , 22 , 31 , 32 , 34 – 41 , 43 , 44 ].…”

“…However, challenges of this method include unknown taxon-specific trophic discrimination factor and β values for many taxa, as well as the requirement for additional data collection for fingerprinting of δ 13 C and δ 15 N [ 42 ]. Overall, both bulk and CSIA retrospective studies on Arctic and North Atlantic marine mammals present either that δ 13 C and δ 15 N increase, decrease or stay the same of over time in the different areas and across species [ 22 , 31 , 34 , 36 , 37 , 39 – 41 , 43 , 44 ] (Tables S1 & S2 ). This suggests that top predators’ trophic ecologies respond to ecosystem changes in diverse and inconsistent ways.…”