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

• Main Authors: Pfister, Catherine A., Roy, Kaustuv, Wootton, J. Timothy, McCoy, Sophie J., Paine, Robert T., Suchanek, Thomas H., Sanford, Eric
• Format: Dataset
• Language: English
• Published: Dryad 2016
• Subjects: ocean acidification; California mussel; California Current Large Marine Ecosystem; ocean pH; 2500 y BP to present; Mytilus californianus; modern day; shell thickness; Ocean acidification
• Online Access: https://dx.doi.org/10.5061/dryad.rr853; http://datadryad.org/stash/dataset/doi:10.5061/dryad.rr853

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. : Modern_archival_midden_comparison_fig1Mytilus californianus data used in Fig 1 of the ms with measurements of shell dimensions, masses, age, thickness and radiocarbon data, where applicable.Tatoosh_Archival_Small_Myt_californianusMytilus californianus morphological data from Tatoosh Island for modern and archival mussels. These data were used in Figs 2 and 3 of the manuscript.