Award: OCE-2129942

Coastal marine organisms experience a broad range of stressors, including stressors associated with seawater chemistry.  For instance, increases in the concentration of hydrogen ions in seawater and declines in the saturation level of the ionic molecule, calcium carbonate, impact marine life.  Both changes accompany “ocean acidification,” a global phenomenon caused by human-produced atmospheric carbon dioxide entering the sea.  Ocean acidification decreases calcification, growth, reproduction, settlement, and survival of a wide variety of marine species. However, a complete understanding of the origins of these negative consequences remains elusive.

Our research explored the mechanistic underpinnings of how seawater chemistry influences the ability of ocean animals to produce shells.  While not all marine species create shells, many do, including ecologically and economically important organisms like mussels, oysters, and marine snails.  We used laboratory manipulations of seawater chemistry to tease apart key drivers of shell calcification, ensuring that all chemical conditions equated to ones arising in nature.  We then cultured organisms under the altered seawater conditions while simultaneously quantifying rates of shell calcification.

The above protocol involved more than 400 distinct incubations of individual animals.  Results showed that shell calcification rates in two species of coastal mussels (the California mussel, Mytilus californianus; and the Northern Blue mussel, M. trossulus), as well as in a widespread shoreline gastropod (the Black Turban snail, Tegula funebralis) all depend on concentrations of both hydrogen ions and bicarbonate ions in seawater.  A third species of mussel, M. galloprovincialis (the Mediterranean mussel), appears to exhibit the same pattern, although more data are required for full certainty.  The discovery of the dual role of bicarbonate and hydrogen ions deviates from traditional models of calcification that emphasize the importance of saturation levels of calcium carbonate in seawater.  Data collected in conjunction with the chemical manipulations additionally demonstrated that shell dissolution under ocean acidification conditions in Mytilus trossulus is markedly faster than in its closest relatives.  Such sensitivity implies greater species-specific vulnerability than has often been anticipated.  In other experiments, we documented a strong role of the outer organic covering of mussel shells in resisting shell dissolution.  Although a protective capacity for the organic layer had been hypothesized previously, our work was the first to directly test this conjecture.

The project’s broader impacts extended to supporting education, training, and early career development of graduate students and undergraduates at UC Davis, as well as local community college undergraduates who participated in a joint internship program established between UC Davis and Santa Rosa Junior College.  All individuals gained research skills and expertise.  A subset, in particular, learned tools for quantifying seawater chemistry, techniques for culturing invertebrates, and how to set up and conduct incubations requiring complex chemical manipulations.  Each student was exposed to the scientific process, including the concept of hypothesis testing, principles of experimental design, quantitative data analysis, and professional writing.

 

Last Modified: 05/30/2026
Modified by: Brian P Gaylord