Seawater carbonate chemistry and biomineralization pathways and shell material properties of Magallana gigas and Mytilus spp.

Molluscs are among the organisms affected by ocean acidification (OA), relying on carbon for shell biomineralization. Metabolic and environmental sourcing are two pathways potentially affected by OA, but the circumstances and patterns by which they are altered are poorly understood. From previous studies, mollusc shells grown under OA appear smaller in size, brittle and thinner, suggesting an important alteration in carbon sequestration. However, supplementary feeding experiments have shown promising results in offsetting the negative consequences of OA on shell growth. Our study compared carbon uptake by δ13C tracing and deposition into mantle tissue and shell layers in Magallana gigas and Mytilus species, two economically valuable and common species. After subjecting the species to 7.7 pH, +2 °C seawater, and enhanced feeding, both species maintain shell growth and metabolic pathways under OA without benefitting from extra feeding, thus, showing effective acclimation to rapid and short-term environmental change. Mytilus spp. increases metabolic carbon into the calcite and environmental sourcing of carbon into the shell aragonite in low pH and high temperature conditions. Low pH affects M. gigas mantle nitrogen isotopes maintaining growth. Calcite biomineralization pathway differs between the two species and suggests species-specific response to OA.软体动物是受海洋酸化（OA）影响的生物类群之一，其贝壳生物矿化过程依赖碳源供给。代谢碳获取与环境碳获取是两类可能受海洋酸化影响的途径，但其受影响的具体情形与变化模式仍尚不明确。既往研究显示，海洋酸化环境下培育的软体动物贝壳尺寸更小、质地更脆且更薄，这表明其碳固存过程发生了显著改变。不过，补充投喂实验已展现出可观效果，可抵消海洋酸化对贝壳生长带来的负面影响。本研究通过碳同位素δ¹³C示踪技术，对比分析了长牡蛎（Magallana gigas）与贻贝属（Mytilus）两种兼具经济价值与广泛分布性的物种的碳摄取过程，及其在外套膜组织与贝壳各层中的沉积模式。将这两类物种置于pH7.7、水温升高2℃的海水环境并进行强化投喂后，两种生物在海洋酸化条件下均能维持贝壳生长与代谢通路，且未从额外投喂中获益，由此表明它们可有效适应快速短期的环境变化。在低pH与高温环境下，贻贝属物种会增加向方解石组分供应的代谢源性碳，以及向贝壳文石组分供应的环境源性碳。低pH条件会影响长牡蛎外套膜的氮同位素组成，以维持其生长。两种物种的方解石生物矿化途径存在显著差异，这表明它们对海洋酸化的响应具有物种特异性。