Abstract. The Baltic Sea has a salinity gradient decreasing from fully marine (> 25) in the West to below 7 in the Central Baltic Proper. Reef forming mytilid mussels exhibit decreasing growth when salinity 3⁻] and [Ca²⁺] also decrease with salinity, challenging calcifying organisms through CaCO₃ undersaturation (Ω ≤ 1) and unfavourable ratios of calcification substrate (Ca²⁺ and HCO₃⁻) to inhibitor (H⁺). In this study we assessed the impact of isolated individual factors (salinity, [Ca²⁺], [HCO₃⁻] and pH) on calcification and growth of mytilid mussel populations along the Baltic salinity gradient. Laboratory experiments rearing juvenile Baltic Mytilus at a range of salinities (6, 11 and 16), HCO₃⁻ concentrations (300–2100 µmol kg⁻¹) and Ca²⁺ concentrations (0.5–4 mmol kg⁻¹) were coupled with field monitoring in three Baltic mussel reefs. Results reveal that as individual factors, low [HCO₃⁻], pH and salinity cannot explain low calcification rates in the Baltic Sea. Calcification rates are impeded when Ω_aragonite ≤ 1 or the substrate inhibitor ratio ≤ 0.7, primarily due to [Ca²⁺] limitation which corresponds to a salinity of ca. 11. Increased food availability may be able to mask these negative impacts, but not when seawater conditions are permanently adverse, as observed in two Baltic reefs at salinities 2+] which may lead to a westward distribution shift of marine calcifiers. It is therefore vital to understand the mechanisms by which the ionic composition of seawater impacts bivalve calcification for better predicting the future of benthic Baltic ecosystems.

中文翻译：

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盐度和碳酸盐化学的解耦：波罗的海贻贝的钙离子浓度低而不是盐度限制了钙化

摘要。波罗的海的盐度梯度从西部的完全海洋（> 25）下降到中波罗的海中部的7以下。礁形成mytilid贻贝表现出降低的生长当盐度3 ^- ]和[钙²⁺ ]也降低与盐度，通过碳酸钙挑战钙化生物体₃欠饱和（Ω≤1）和钙化基板的不利比率（CA ²⁺和HCO ₃ ^- ）抑制剂（H ⁺）。在这项研究中，我们评估分离个体因素（盐度，[Ca的冲击²⁺ ]，[HCO ₃ ^-和pH值）对波罗的海盐度梯度上的贻贝贻贝种群钙化和生长的影响。实验室实验饲养少年巴尔贻贝以一定范围的盐度（6,11和16），HCO的₃ ^-浓度（300-2100微摩尔千克^-1）和Ca ²⁺浓度（0.5-4毫摩尔千克^-1）偶联与现场在三个波罗的海贻贝礁进行监测。结果表明，作为单独的因素，低的[HCO ₃ ^- ]，pH和盐度不能解释波罗的海的低钙化率。当Ω_文石 ≤1或底物抑制剂比率≤0.7时，钙化速率受到阻碍，这主要是由于[Ca ²⁺]极限，对应于盐度约。11.增加的粮食供应量可能能够掩盖这些负面影响，但当海水状况永久不利时，却无法掩盖这一点，正如在盐度为2+的两个波罗的海礁所观察到的那样，这可能导致海洋钙化剂向西移动。因此，至关重要的是要了解海水的离子组成影响双壳类钙化的机制，以便更好地预测底栖波罗的海生态系统的未来。