Historical baselines and the future of shell calcification for a foundation species in a changing ocean.
Seawater pH and the availability of carbonate ions are 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 suggests 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.
Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA cpfister@uchicago.edu.
Catherine A
CA
Pfister
Section of Ecology, Behavior and Evolution, University of California, San Diego, CA, USA.
Kaustuv
K
Roy
Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA.
J Timothy
JT
Wootton
Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA Department of Biological Science, Florida State University, Tallahassee, FL, USA.
Sophie J
SJ
McCoy
Department of Biology, University of Washington, Seattle, WA, USA.
Robert T
RT
Paine
US Geological Survey, Western Ecological Research Center, University of California, Davis, Davis, CA, USA Bodega Marine Laboratory and Department of Wildlife, Fish and Conservation Biology, University of California, Davis, Davis, CA, USA.
Thomas H
TH
Suchanek
Bodega Marine Laboratory and Department of Evolution and Ecology, University of California, Davis, Davis, CA, USA.
Eric
E
Sanford
D060105:Animal Shells / Q000737:chemistry*; D000818:Animals; D002113:Calcification, Physiologic; D002140:California; D006863:Hydrogen-Ion Concentration; D049878:Mytilus / Q000254:growth & development*; D009792:Oceans and Seas; D012623:Seawater / Q000737:chemistry
California current large marine ecosystem; California mussel; Mytilus californianus; ocean acidification; ocean pH; shell thickness