Potential effects of ocean acidification on Alaskan corals based on calcium carbonate mineralogy composition analysis (NCEI Accession 0157223)

Effects of ocean acidification (OA) on deep-sea coral habitats in Alaska could be pronounced given the particularly shallow and rapidly shoaling calcite and aragonite saturation horizons in the region. The magnitude of potential effects could partially depend on the corals' calcium carbonate mineralogy. We used X-ray diffraction and powerful full-pattern Rietveld data refinement to precisely determine the skeletal composition of 62 species of Alaskan corals-the most comprehensive cold-water coral dataset for any region of the world. Alaskan corals have complex mineralogy, including a high percentage of slightly polymorphic taxa. Scleractinians and octocorals were principally aragonite and calcite, respectively. A few octocorals were composed of the most soluble form of calcium carbonate (high-Mg calcite). Hydrocorals have the most complex mineralogy with many polymorphic taxa, and some genera have both aragonite and calcite species. Most coral taxa live at least partially below the current saturation horizons so may be physiologically compensating for the effects of OA via important life-history trade-offs. We found evidence of mineral-switching related to depth distribution or broad-scale biogeography. All Alaskan corals are protected by organic tissue and may have the ability to up-regulate the pH of internal calcifying fluid relative to ambient seawater. No Alaskan corals are at risk for skeletal dissolution based on present-day carbonate chemistry conditions in the North Pacific Ocean although the carbonate mineralogy of a few taxa may approach estimated dissolution points. Alaska's ecologically most important corals (Primnoa pacifica and Stylaster spp.) are most at risk to potential effects of OA given their highly soluble skeletons, depth distribution, and observed propensity for tissue loss from contact with fishing gear and predation. Laboratory experiments are currently underway to determine if Primnoa pacifica can tolerate carbonate chemistry conditions predicted for year 2100 and maintain important life-history functions.

鉴于阿拉斯加海域的方解石与文石饱和层格外浅薄且快速抬升，海洋酸化（OA）对该区域深海珊瑚栖息地的影响可能十分显著。潜在影响的严重程度，在一定程度上取决于珊瑚的碳酸钙矿物学特征。本研究采用X射线衍射（X-ray diffraction）与高精度全谱里特韦尔数据精修法，精准测定了62种阿拉斯加珊瑚的骨骼组成——这是目前全球范围内单一区域覆盖最全面的冷水珊瑚数据集。阿拉斯加珊瑚的矿物组成复杂，包含较高比例的轻度多态类群。石珊瑚目与八放珊瑚分别主要由文石与方解石构成；少数八放珊瑚则由溶解度最高的碳酸钙形式——高镁方解石组成。水螅珊瑚的矿物组成最为复杂，包含诸多多态类群，部分属同时涵盖文石与方解石类群。多数珊瑚类群至少有部分种群栖息于当前饱和层之下，因此可能通过关键的生活史权衡机制，在生理层面补偿海洋酸化带来的影响。本研究发现了与深度分布或大范围生物地理格局相关的矿物转换证据。所有阿拉斯加珊瑚均有有机组织保护，且具备相对于周围海水上调内部钙化液pH值的能力。基于北太平洋当前的碳酸盐化学条件，暂无阿拉斯加珊瑚面临骨骼溶解风险，但少数类群的碳酸盐矿物组成可能接近估算的溶解临界点。阿拉斯加海域生态意义最为关键的珊瑚（Primnoa pacifica与Stylaster spp.），由于其骨骼溶解性高、深度分布特征，以及已观测到的因渔具接触和捕食导致组织流失的倾向，最易受到海洋酸化潜在影响的威胁。目前相关实验室实验正在开展，以验证Primnoa pacifica能否耐受2100年预测的碳酸盐化学条件，并维持其关键生活史功能。