Data from: Historical baselines and the future of shell calcification for a foundation species in a changing ocean

Seawater pH and the availability of carbonate ions is decreasing due to anthropogenic carbon dioxide emissions, posing challenges for calcifying marine species. Marine mussels are of particular concern given their role as foundation species worldwide. Here, we document shell growth and calcification patterns in Mytilus californianus, the California mussel, over millennial and decadal scales. By comparing shell thickness across the largest modern shells, the largest mussels collected in the 1960s-1970s and shells from two Native American midden sites (1000-2420 years BP), we found that modern shells are thinner overall, thinner per age category, and thinner per unit length. Thus, the largest individuals of this species are calcifying less now than in the past. Comparisons of shell thickness in smaller individuals over the past 10-40 years, however, do not show significant shell thinning. Given our sampling strategy, these results are unlikely to simply reflect within-site variability or preservation effects. Review of environmental and biotic drivers known to affect shell calcification suggest declining ocean pH as a likely explanation for the observed shell thinning. Further future decreases in shell thickness could have significant negative impacts on M. californianus survival and, in turn, negatively impact the species rich complex that occupies mussel beds.

受人为二氧化碳排放影响，海水pH值与碳酸盐离子可用性持续下降，给钙化海洋生物带来严峻生存挑战。海洋贻贝作为全球分布的关键奠基物种，其生存状况尤其值得关注。本研究针对加州贻贝（Mytilus californianus），记录了其在千年与十年尺度下的壳体生长与钙化模式。通过对比现代最大个体壳体、1960至1970年代采集的最大贻贝壳体，以及两处北美原住民贝冢遗址（距今1000~2420年）出土的壳体厚度，研究发现现代壳体整体厚度更低，同年龄组别壳体更薄，单位长度对应的壳体厚度也更小。因此，该物种现存的最大个体，其钙化程度已较过去显著下降。不过，对过去10至40年间采集的小型个体壳体厚度的对比分析，并未观测到显著的壳体减薄现象。结合本次采样策略来看，上述结果不太可能仅由遗址内部变异或保存效应所导致。通过梳理已知影响壳体钙化的环境与生物驱动因子，研究认为海水pH值下降是观测到的壳体减薄现象的合理解释。若未来壳体厚度持续降低，将对加州贻贝的生存造成显著负面影响，并进而波及栖息于贻贝床的物种丰富群落。