Environmentally-forced mineralogical change has implications for both strength and solubility of skeletal carbonate. Three marine invertebrates from the southern hemisphere were grown for 50 days in artificial seawater with different Mg/Ca ratios (1.5, 2.5, 3.5, 4.5 and 5.3). Blue mussels (Mytilus edulis) and jingle oysters (Anomia trigonopsis) showed no changes in mineralogy. Blue tubeworms (Spirobranchus cariniferus) were able to maintain their typical mineralogical composition (calcite with 8–12 wt% MgCO₃) at most seawater Mg concentrations. However, at the lowest Mg/Ca ratio (1.5), the tubeworms precipitated calcite with significantly lower amounts of MgCO₃ (2–4 wt% MgCO₃). Current models of passive calcification, based on a linear relationship between seawater Mg/Ca and calcite Mg content, do not accurately reflect this Mg-dependent stepwise change in minerology among organisms with an active calcification strategy. We propose a new “tipping-point” model that better describes the calcification response of blue tubeworms to changing environmental conditions. The boundary of this active/passive tipping point may be species-specific and may have consequences for preservation, alteration, and resilience of marine skeletal carbonate.

环境强迫的矿物学变化对骨骼碳酸盐的强度和溶解度都有影响。来自南半球的三种海洋无脊椎动物在不同 Mg/Ca 比（1.5、2.5、3.5、4.5 和 5.3）的人造海水中生长了 50 天。蓝贻贝（Mytilus edulis）和叮当牡蛎（ Anomia trigonopsis ）的矿物学没有变化。蓝管虫（Spirobranchus cariniferus）能够在大多数海水镁浓度下保持其典型的矿物学组成（含 8-12 wt% MgCO _{3的方解石）。然而，在最低 Mg/Ca 比 (1.5) 下，管虫沉淀出的方解石的 MgCO 3}含量显着降低（2-4 wt% MgCO ₃）。当前的被动钙化模型基于海水 Mg/Ca 和方解石 Mg 含量之间的线性关系，并不能准确反映具有主动钙化策略的生物体中这种 Mg 依赖的逐步矿物学变化。我们提出了一种新的“临界点”模型，可以更好地描述蓝管虫对不断变化的环境条件的钙化反应。这个主动/被动临界点的边界可能是特定于物种的，并且可能对海洋骨骼碳酸盐的保存、改变和恢复产生影响。