Investigating controls of shell growth features in a foundation bivalve species: seasonal trends and decadal changes in the California mussel

• Published in: Biogeosciences Vol. 19; no. 2; pp. 329 - 346
• Main Authors: Vriesman, Veronica Padilla, Carlson, Sandra J, Hill, Tessa M
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 20-01-2022; Copernicus Publications
• Subjects: Aragonite; Archaeology; Archives & records; Bivalvia; Calcification; Calcite; Calcite crystals; Carbonates; Coasts; Environmental control; Food; Growth; Influence; Investigations; Light; Marine molluscs; Metabolism; Mineralogy; Mollusks; Mytilus californianus; Ocean circulation; Oceanographic variability; Salinity; Seasonal variations; Seasonality; Seasons; Seawater; Shellfish; Shells; Shells (structural forms); Trends; Upwelling; Winter; California; United States > US
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-19-329-2022

Marine bivalve mollusk shells can offer valuable insights into past oceanographic variability and seasonality. Given its ecological and
archeological significance, Mytilus californianus (California mussel) presents the opportunity to examine seasonal and decadal changes
recorded in its shell over centuries to millennia. While dark–light growth bands in M. californianus shells could be advantageous for
reconstructing past environments, uncertainties remain regarding shell structure, environmental controls of dark–light-band formation, and the
amount of time represented by a dark–light pair. By analyzing a suite of M. californianus shells collected in 2002, 2003, 2019, and 2020
from Bodega Bay, California, we describe the mineralogical composition; establish relationships among the growth band pattern, micro-environment, and
collection season; and compare shell structure and growth band expression between the archival (2002–2003) and modern (2019–2020) shells. We
identified three mineralogical layers in M. californianus: an outer prismatic calcite layer, a middle aragonite layer, and a secondary
inner prismatic calcite layer, which makes M. californianus the only Mytilus species to precipitate a secondary calcite
layer. Within the inner calcite layer, light bands are strongly correlated with winter collection months and could be used to reconstruct periods
with moderate, stable temperatures and minimal upwelling. Additionally, modern shells have significantly thinner inner calcite layers and more
poorly expressed growth bands than the archival shells, although we also show that growth band contrast is strongly influenced by the
micro-environment. Mytilus californianus from northern California is calcifying differently, and apparently more slowly, than it was
20 years ago.