Reductions to seawater pH challenge the shell integrity of marine calcifiers. Many molluscs have an external organic layer (the periostracum) that limits exposure of underlying shell to the external environment, which could potentially help combat shell dissolution under corrosive seawater conditions. We tested this possibility in adult California mussels, Mytilus californianus. We quantified shell dissolution rates as a function of periostracum cover across three levels of reduced pH (7.7, 7.5, and 7.4 on the total scale). This dataset represents shell dissolution data of California Mussels as a function of shell periostracum cover and pH level from lab experiments conducted at the Bodega Marine Laboratory, University of California, Davis in July and August 2022. For the current study, adult mussels (42 - 64 mm in length) were collected from Marshall Gulch, California (38.369738 °N, -123.073921 °W) between August 2021 and March 2022 and transported immediately to the University of California Davis’ Bodega Marine Laboratory (< 30 min distance), in Bodega Bay, California. Mussels were held in filtered, flow-through seawater and fed ad libitum until used in experiments.

Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Related Datasets
• Parameters
• Project Information
• Funding

Data analysis: We performed computations with R statistical software, RStudio version 2023.06.2. We performed carbonate system calculations using the package seacarb. We analyzed the influence of periostracum cover on CaCO3 shell dissolution in M. californianus adults for trials at pH = 7.5 using a multiple effects linear model where dissolution rate was normalized to shell surface area (mm2) to account for variations in shell size. Normalized dissolution rates were square root transformed to meet linearity requirements for normally distributed residuals. We used backward stepwise model selection using F test significance as the criteria for omitting terms, resulting in a final model that employed both percent periostracum cover and valve length as fixed predictors. Throughout model selection tests, trial date did not significantly explain variability as a random effect so was omitted. Model residual homoscedasticity was verified using a Breusch-Pagan test (BP = 1.0525, df = 2, p-value = 0.5908), and assumptions of linearity and additivity were assessed visually using model residual and QQ-plots.

 

Additionally, we used a separate multiple effects linear model across the two additional pH levels (pH = 7.4, 7.7) to assess how seawater pH independently affects patterns of dissolution. Here, we included pH as a numerical fixed predictor, alongside periostracum cover. Due to a constrained sampling size and narrow range of shell lengths (52 mm ± 4 mm SD), shell length was not included as a fixed predictor in this model in order to conserve degrees of freedom. Normalized CaCO3 dissolution rate was again square root transformed, and backward stepwise model selection was used to estimate the significance of fixed predictors. A Breusch-Pagan test confirmed residual homoscedasticity (BP = 3.5024, df = 3, p-value = 0.3204), and other assumptions were assessed visually as before. 

Coverage: California coast, USA

NSF Award Abstract:
This research is exploring the capacity of coastal organisms to cope with alterations in seawater chemistry driven by both freshwater inputs and absorption of carbon dioxide into the world's oceans (ocean acidification). The project focuses on calcification responses and behavioral impairments of shoreline animals under altered seawater chemistry, and forefronts a common mussel species (the California mussel), and a common snail (the black turban snail), each abundant on rocky shores along the west coast of North America. The target species operate as exemplar organisms for characterizing the responses of marine invertebrates more generally. Methods involve experimental decoupling of multiple components of the carbonate system of seawater to isolate drivers that are difficult to separate otherwise. Broader impacts include transfer of scientific information to policy-makers, including legislators, as well as training and skill-set development of future generations of scientists and citizens. One Ph.D. student is supported, as are UC Davis undergraduates conducting mentored research. The project also provides research internships for undergraduates from a local community college (Santa Rosa Junior College), many of whom are from underrepresented groups. The latter project component substantially bolsters an ongoing program at Bodega Marine Laboratory that includes efforts in diversity, equity, and inclusion. Data and interpretations from the project are feeding into an existing educational program that links to local K-12 schools and reaches ~10,000 members of the public each year.

Overall, the research of the project is dissecting drivers of calcification and behavioral disruption in key shoreline invertebrates, across present-day and future carbonate system conditions appropriate to coastal marine environments. Efforts are exploring the extent to which calcification depends on one versus multiple parameters of the seawater carbonate system. In particular, existing conceptual models emphasize the importance of calcium carbonate saturation state (Ω) and/or the ratio of bicarbonate to hydrogen ion concentrations ([HCO3-]/[H+]), and the project is examining these mechanisms as well as the possibility that more than one driver acts simultaneously. It is doing so both in bivalves and in gastropods to test for generality across mollusks. The project is additionally examining whether pH is the only carbonate system factor contributing to known patterns of behavioral impairment in marine invertebrates. Leading explanations for debilitating behaviors induced by ocean acidification involve altered ion channel function, but discussion in the literature continues, and studies that explicitly decouple the carbonate system are necessary.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.