• Estimates of primary production sources to Arctic bivalves using amino acid stable carbon isotope fingerprinting

      Rowe, Audrey G.; Wooller, Matthew; Iken, Katrin; O'Brien, Diane (2018-12)
      Benthic invertebrates are a crucial trophic link in Arctic marine food webs. However, estimates of the contribution of primary production sources sustaining these organisms are not well characterized. Potential sources could include sinking particulate organic matter from sea ice algae and phytoplankton, terrestrial organic matter eroded from the coastal environment, macroalgal material, or microbial organic matter. Proportions of these sources could also be significantly altered in the future as a result of environmental change. We measured the stable carbon isotope values of essential amino acids in muscle tissue from two common bivalve genera (Macoma spp. and Astarte spp.) collected in Hanna Shoal in the northeastern Chukchi Sea, considered an Arctic benthic hotspot. We used stable isotope mixing models in R (simmr) to compare the stable carbon isotope amino acid fingerprints of the bivalves to a suite of amino acid source endmembers, including marine phytoplankton, brown and red macroalgae, bacteria, and terrestrial plants, to estimate the proportional contributions of primary production sources to the bivalve species from Hanna Shoal. The models revealed relatively high contributions of essential amino acids from phytoplankton and bacteria averaged across both species in the region as a whole. We also examined whether stable carbon isotope fingerprints could be measured from essential amino acids preserved in bivalve shells, which could then allow proportional contributions of food sources to be estimated from ancient bivalve shells, allowing source estimates to be extended back in time. To investigate this, we measured the stable carbon isotope values of essential amino acids in a suite of paired modern bivalve shells and muscle from Macoma calcarea from the Chukchi Sea. These analyses revealed a correspondence between the fingerprints and mixing model estimates of the dominant primary production source of essential amino acids derived from analyses of these two tissue types. Our findings indicate that stable carbon isotope amino acid fingerprinting of marine bivalves can be used to examine dominant organic matter sources in the Arctic marine benthos in recent years as well as in deeper time.
    • Tracing sea ice algae into various benthic feeding types on the Chukchi Sea shelf

      Schollmeier, Tanja; Iken, Katrin; Wooller, Matthew; Hardy, Sarah (2018-12)
      Climate change in the Arctic is expected to have drastic effects on marine primary production sources by shifting ice-associated primary production to an overall greater contribution from pelagic primary production. This shift could influence the timing, amount, and quality of algal material reaching the benthos. We determined the contribution of sea ice particulate organic matter (iPOM) to benthic-feeding invertebrates by examining concentrations and stable carbon isotope values (expressed as δ¹³C values) of three FAs prominent in diatoms: 16:4(n-1), 16:1(n-7) and 20:5(n-3). Our underlying assumption was that diatoms make up the majority in sea ice algal communities compared with phytoplankton communities. According to the FA concentrations, subsurface deposit feeders consumed the most iPOM and suspension feeders the least. Conversely, there were little differences in δ¹³C values of FAs between deposit and suspension feeders, but the higher δ¹³C values of 16:1(n-7) in omnivores indicated greater consumption of iPOM. We suggest that omnivores accumulate the ice algal FA biomarker from their benthic prey, which in turn may feed on ice algae from a deposited sediment pool. The dissimilar results between FA concentrations and isotope values suggest that the FAs used here may not be sufficiently source-specific and that other unaccounted for production sources, such as bacteria, may also contribute to the FA pool. We propose that FA isotope values are a more indicative biomarker than FA concentrations, but there is a further need for more specific ice algal biomarkers to resolve the question of ice algal contributions to the Arctic benthic food web.