It has been argued that skeletal Mg/Ca ratio in echinoderms is mostly governed by Mg²⁺ and Ca²⁺ concentrations in the ambient seawater. Accordingly, well‐preserved fossil echinoderms were used to reconstruct Phanerozoic seawater Mg²⁺/Ca²⁺ ratio. However, Mg/Ca ratio in echinoderm skeleton can be affected by a number of environmental and physiological factors, the effects of which are still poorly understood. Notably, experimental data supporting the applicability of echinoderms in paleoenvironmental reconstructions remain limited. Here, we investigated the effect of ambient Mg²⁺/Ca²⁺ seawater ratio and diet on skeletal Mg/Ca ratio and growth rate in two echinoid species (Psammechinus miliaris and Prionocidaris baculosa). Sea urchins were tagged with manganese and then cultured in different Mg²⁺/Ca²⁺ conditions to simulate fluctuations in the Mg²⁺/Ca²⁺ seawater ratios in the Phanerozoic. Simultaneously, they were fed on a diet containing different amounts of magnesium. Our results show that the skeletal Mg/Ca ratio in both species varied not only between ossicle types but also between different types of stereom within a single ossicle. Importantly, the skeletal Mg/Ca ratio in both species decreased proportionally with decreasing seawater Mg²⁺/Ca²⁺ ratio. However, sea urchins feeding on Mg‐enriched diet produced a skeleton with a higher Mg/Ca ratio. We also found that although incubation in lower ambient Mg²⁺/Ca²⁺ ratio did not affect echinoid respiration rates, it led to a decrease or inhibition of their growth. Overall, these results demonstrate that although skeletal Mg/Ca ratios in echinoderms can be largely determined by seawater chemistry, the type of diet may also influence skeletal geochemistry, which imposes constraints on the application of fossil echinoderms as a reliable proxy. The accuracy of paleoseawater Mg²⁺/Ca²⁺ calculations is further limited by the fact that Mg partition coefficients vary significantly at different scales (between species, specimens feeding on different types of food, different ossicle types, and stereom types within a single ossicle).

中文翻译：

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海水中Mg2 + / Ca2 +的比例和饮食对海胆生物矿化和生长以及棘皮动物棘皮动物与古环境重建的相关性的影响。

有人认为棘皮动物骨骼中Mg / Ca的比例主要受周围海水中Mg ²⁺和Ca ²⁺浓度的控制。因此，保存完好的化石棘皮动物被用来重建生代海水Mg ²⁺ / Ca ^2+的比例。但是，棘皮动物骨骼中的Mg / Ca比值可能会受到许多环境和生理因素的影响，其影响仍然知之甚少。值得注意的是，支持棘皮动物在古环境重建中的适用性的实验数据仍然有限。在这里，我们研究了环境Mg ²⁺ / Ca ²⁺海水比例和饮食对两种棘突类动物骨骼Mg / Ca比和生长速率的影响（s（Psammechinus miliaris）和杆状（Prionocidaris baculosa）。用锰标记海胆，然后在不同的Mg ²⁺ / Ca ²⁺条件下培养，以模拟古生代Mg ²⁺ / Ca ²⁺海水比例的波动。同时，以含不同量镁的饮食喂养它们。我们的研究结果表明，这两种物种的骨骼Mg / Ca比率不仅在小骨类型之间变化，而且在单个小骨中不同类型的车体之间也变化。重要的是，这两个物种的骨骼Mg / Ca比值均与海水Mg ²⁺ / Ca ^2+的降低成比例地降低比。但是，以富含镁的饮食为食的海胆产生的骨骼具有较高的Mg / Ca比。我们还发现，尽管以较低的环境Mg ²⁺ / Ca ²⁺比例孵育不会影响类神经纤维的呼吸速率，但会导致其生长速度降低或受到抑制。总体而言，这些结果表明，尽管棘皮动物骨骼中Mg / Ca的比例在很大程度上可以通过海水化学方法确定，但饮食的类型也可能影响骨骼地球化学，这对化石棘皮动物作为可靠的替代品的应用施加了限制。古水Mg ²⁺ / Ca ²⁺的准确性 Mg的分配系数在不同的尺度上（物种之间，以不同类型的食物为食的标本，不同的小骨类型和单个小骨中的定型类型之间）的变化显着，这一事实进一步限制了计算。