Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, PL-00-818, Warsaw, Poland.
Université Libre de Bruxelles, Faculté des Sciences, Laboratoire de Biologie Marine, CP 160/15, av. F.D. Roosevelt, 50 B-1050, Bruxelles, Belgium.
Mar Environ Res. 2019 Mar;145:22-26. doi: 10.1016/j.marenvres.2019.02.006. Epub 2019 Feb 10.
It has been argued that concentration of major metallic ions such as Mg and Ca plays a role in determining the composition of the echinoderm skeleton. Consequently, in several studies Mg/Ca ratio from modern and fossil echinoderm ossicles was used as a proxy of secular Mg/Ca changes of Phanerozoic seawater. However, although significant progress has been made in understanding biomineralization of echinoderms, it is still largely unknown what are the sources and physiological pathways of major ions that contribute to skeleton formation. Herein we tested the effects of modifications of ambient seawater Mg/Ca ratio (which is typically ∼5) and Mg-enrichment of the diet on the Mg/Ca ratio in regenerating spines of sea urchin Paracentrotus lividus under experimental conditions. We found that sea urchins cultured in seawater with Mg/Ca ratio decreased to ∼1.9 produced a skeleton with also decreased Mg/Ca ratio. However, the skeleton of specimens fed on a Mg-enriched diet showed significantly higher Mg/Ca ratio. This suggests that the seawater is an important but not the only source of ions that contributes to the Mg/Ca ratio of the skeleton. Consequently, the reliability of geochemical models that link directly seawater chemistry with the Mg/Ca ratio of the skeleton should be reevaluated.
有人认为，主要金属离子（如 Mg 和 Ca）的浓度在决定棘皮动物骨骼的组成方面起着作用。因此，在几项研究中，现代和化石棘皮动物骨片的 Mg/Ca 比值被用作 Phanerozoic 海水 Mg/Ca 变化的代用指标。然而，尽管在理解棘皮动物的生物矿化方面已经取得了重大进展，但对于形成骨骼的主要离子的来源和生理途径仍知之甚少。在这里，我们测试了改变环境海水 Mg/Ca 比值（通常约为 5）和饮食中 Mg 富集对实验条件下棘皮动物海胆 Paracentrotus lividus 再生刺的 Mg/Ca 比值的影响。我们发现，在 Mg/Ca 比值降至约 1.9 的海水中培养的海胆产生的骨骼 Mg/Ca 比值也降低了。然而，喂食富含 Mg 的饮食的标本的骨骼显示出明显更高的 Mg/Ca 比值。这表明海水是离子的重要但不是唯一来源，这些离子有助于骨骼的 Mg/Ca 比值。因此，应该重新评估将海水化学与骨骼的 Mg/Ca 比值直接联系起来的地球化学模型的可靠性。
