Iron assimilation by the clam Laternula elliptica: Do stable isotopes (δ56Fe) help to decipher the sources?

Iron stable isotope signatures (delta Fe-56) in hemolymph (bivalve blood) of the Antarctic bivalve Laternula elliptica were analyzed by Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS) to test whether the isotopic fingerprint can be tracked back to the predominant sources of the assimilated Fe. An earlier investigation of Fe concentrations in L. elliptica hemolymph suggested that an assimilation of reactive and bioavailable Fe (oxyhydr)oxide particles (i.e. ferrihydrite), precipitated from pore water Fe around the benthic boundary, is responsible for the high Fe concentration in L. elliptica (Poigner et al., 2013b). At two stations in Potter Cove (King George Island, Antarctica) bivalve hemolymph showed mean delta Fe-56 values of -1.19 +/- 0.34 parts per thousand and -1.04 +/- 0.39 parts per thousand, respectively, which is between 0.5%, and 0.85%e lighter than the pool of easily reducible Fe (oxyhydr)oxides of the surface sediments (-0.3 parts per thousand to -0.6 parts per thousand). This is in agreement with the enrichment of lighter Fe isotopes at higher trophic levels, resulting from the preferential assimilation of light isotopes from nutrition. Nevertheless, delta Fe-56 hemolymph values from both stations showed a high variability, ranging between 0.21%. (value close to unaltered/primary Fe(oxyhydr)oxide minerals) and -1.91 parts per thousand (typical for pore water Fe or diagenetic Fe precipitates), which we interpret as a mixed delta Fe-56 signature caused by Fe assimilation from different sources with varying Fe contents and delta Fe-56 values. Furthermore, mass dependent Fe fractionation related to physiological processes within the bivalve cannot be ruled out. This is the first study addressing the potential of Fe isotopes for tracing back food sources of bivalves. (C) 2015 Elsevier Ltd. All rights reserved.