Iron assimilation by the clam Laternula elliptica from Potter Cove, King Georg Island, Antarctica

Iron stable isotope signatures (d56Fe) 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., 2013, doi:10.1016/j.ecss.2013.10.027).
At two stations in Potter Cove (King George Island, Antarctica) bivalve hemolymph showed mean d56Fe values of -1.19 ± 0.34 per mil and -1.04 ± 0.39 per mil, respectively, which is between 0.5 per mil and 0.85 per mil lighter than the pool of easily reducible Fe (oxyhydr)oxides of the surface sediments (-0.3 per mil to -0.6 per mil). 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, d56Fe hemolymph values from both stations showed a high variability, ranging between -0.21 per mil (value close to unaltered/primary Fe(oxyhydr)oxide minerals) and -1.91 per mil (typical for pore water Fe or diagenetic Fe precipitates), which we interpret as a "mixed" d56Fe signature caused by Fe assimilation from different sources with varying Fe contents and d56Fe 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.

本研究通过多接收器电感耦合等离子体质谱法（Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry，MC-ICP-MS），分析了南极双壳类椭圆侧筋蛤（Laternula elliptica）血淋巴（双壳类血液）中的铁稳定同位素特征（d56Fe），以验证该同位素指纹能否追溯至被同化铁的主要来源。此前一项针对椭圆侧筋蛤血淋巴中铁浓度的研究表明，源自底栖边界附近孔隙水中铁沉淀的活性生物可利用性铁（氢氧）氧化物颗粒（即水铁矿（ferrihydrite））的同化作用，是该双壳类血淋巴高铁浓度的成因（Poigner等，2013，doi:10.1016/j.ecss.2013.10.027）。在波特湾（乔治王岛，南极）的两个站位中，双壳类血淋巴的平均d56Fe值分别为-1.19±0.34 ‰和-1.04±0.39 ‰，该值较表层沉积物中易还原铁（氢氧）氧化物库（-0.3 ‰至-0.6 ‰）轻0.5 ‰至0.85 ‰。这一结果与营养过程中轻同位素优先同化导致的更高营养级铁同位素轻富集现象相符。不过，两个站位的血淋巴d56Fe值均表现出较高变异性，范围介于-0.21 ‰（接近未改变的原生铁（氢氧）氧化物矿物）至-1.91 ‰（孔隙水铁或成岩铁沉淀物的典型值）之间，我们将其归因于不同铁含量与d56Fe值的铁源同化作用所形成的“混合”d56Fe特征。此外，双壳类体内生理过程相关的质量依赖性铁分馏效应亦无法排除。本研究是首个探讨铁同位素用于追溯双壳类食物来源潜力的相关研究。