Carbon sources and trophic relationships of ice seals during recent environmental shifts in the Bering Sea

Abstract

Dramatic multiyear fluctuations in water temperature and seasonal sea ice extent and duration across the Bering-Chukchi continental shelf have occurred in this century, raising a pressing ecological question: Do such environmental changes alter marine production processes linking primary producers to upper trophic-level predators? We examined this question by comparing the blubber fatty acid (FA) composition and stable carbon isotope ratios of individual FA (δ 13 C FA ) of adult ringed seals (Pusa hispida), bearded seals (Erignathus barbatus), spotted seals (Phoca largha), and ribbon seals (Histriophoca fasciata), collectively known as "ice seals," sampled during an anomalously warm, low sea ice period in 2002-2005 in the Bering Sea and a subsequent cold, high sea ice period in 2007-2010. δ 13 C FA values, used to estimate the contribution to seals of carbon derived from sea ice algae (sympagic production) relative to that derived from water column phytoplankton (pelagic production), indicated that during the cold period, sympagic production accounted for 62-80% of the FA in the blubber of bearded seals, 51-62% in spotted seals, and 21-60% in ringed seals. Moreover, the δ 13 C FA values of bearded seals indicated a greater incorporation of sympagic FAs during the cold period than the warm period. This result provides the first empirical evidence of an ecosystem-scale effect of a putative change in sympagic production in the Western Arctic. The FA composition of ice seals showed clear evidence of resource partitioning among ringed, bearded, and spotted seals, and little niche separation between spotted and ribbon seals, which is consistent with previous studies. Despite interannual variability, the FA composition of ringed and bearded seals showed little evidence of differences in diet between the warm and cold periods. The findings that sympagic production contributes significantly to food webs supporting ice seals, and that the contribution apparently is less in warm years with low sea ice, raise an important concern: Will the projected warming and continuing loss of seasonal sea ice in the Arctic, and the associated decline of organic matter input from sympagic production, be compensated for by pelagic production to satisfy both pelagic and benthic carbon and energy needs?

Long‐term ecological changes in marine mammals driven by recent warming in northwestern Alaska

“…Bearded seals had δ 15 N values of +16.0 ± 1.0‰ (archaeological, n = 8) and +15.3 ± 0.1‰ (modern, n = 2), suggesting that they fed approximately one trophic level higher than walruses. Ringed seals had δ 15 N values of +18.4 ± 0.9‰ (archaeological, n = 52) and +17.9 ± 0.5 (modern, n = 24), suggesting strong partitioning of dietary resources between ringed and bearded seals, a pattern that has been observed in this region on the basis of blubber fatty acid compositions (Wang et al., ). The average δ 13 C values of archaeological bearded and ringed seals were nearly identical ( p = .95), but the δ 15 N values differed significantly ( p < .001).…”

“…Because of differences in localized water turbidity and its effect on algal cell boundary layer thickness and in turn discrimination against 13 C during CO 2 uptake (France, ), sea ice algae have δ 13 C values that are 5–12‰ higher than pelagic phytoplankton (France, Loret, Mathews, & Springer, ; Hobson, Ambrose, & Renaud, ; Søreide, Hop, Carroll, Falk‐Petersen, & Hegseth, ). Accordingly, the relative importance of pelagic and sympagic production can be approximated on the basis of consumer δ 13 C values (Kohlbach et al., ; Tamelander et al., ), including marine mammals at high trophic levels (Wang et al., ). Additionally, there are gradients in carbon isotope values in particulate organic matter (POM) and consumers between benthic and pelagic habitats, with the latter being characterized by lower δ 13 C values than the former (McConnaughey & Mcroy, ).…”

Pan‐Arctic sea ice‐algal chl a biomass and suitable habitat are largely underestimated for multiyear ice

“…Shifts in the timing of ice algae blooms caused by the different bloom dynamics in MYI vs. FYI, in addition to the presence of reliable ice‐algal habitat in the form of MYI hummocks, however, may affect species which have adapted their life cycles to survival in hitherto MYI‐dominated regions. Many key Arctic species (e.g., copepods, amphipods, polar cod and seals) have demonstrated a high dependency on ice algae derived carbon in almost all regions of the Arctic Ocean (e.g., Budge et al., ; Kohlbach et al., , ; Søreide et al., ; Wang et al., , ). Therefore, we suggest that the disappearance of MYI will have profound pan‐Arctic ecological consequences yet to be fully understood and requires more extensive research efforts in the MYI‐covered central Arctic Ocean.…”

Geographical Area and Life History Traits Influence Diet in an Arctic Marine Predator

“…Biochemical tracers, for instance FA profiles (i.e. the relative proportion of various FA) or nitrogen and carbon stable isotopes, have been used as proxies to describe the foraging niche and diet composition of free-ranging species [ 14 , 35 – 37 ]. This occurs because the chemistry of animal tissues reflects to some degree the biochemical properties of their food.…”