Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Shell collection took place at rocky shore ecosystems spanning ~1,000 kilometers (km) of coastline along the west coast of North America. Shell collections occurred at three wave-exposed rocky headlands in California (Soberanes Point (36°26'50" N, 121°55'44" W), Bodega Marine Reserve (38°19'09" N, 123°04'28" W), Van Damme State Park (39°16'43" N, 123°48'12" W)) and at three wave-exposed rocky headlands in Oregon (Cape Arago (43°18'13" N, 124°24'07" W), Strawberry Hill (44°15'00" N, 124°06'55" W), and Fogarty Creek (44°50'16" N, 124°03'33" W)).

At each of the six study sites, mussels were collected from wave-exposed, mid-intertidal mussel beds. Mussels from 2000-2001 and 2008-2009 were originally collected for different projects. As a result, the sample size and range of mussel shell lengths for each site and time period varied somewhat. The mussel shells from the 2000-2001 time period came from three surveys. First, in 2000, 100 empty/dead mussel shells from Soberanes Point were collected; subsequently, live mussels from a similar range in shell lengths were collected from Strawberry Hill and Fogarty Creek. Second, in 2001, 25 live mussels from a limited size range (55-73 millimeters (mm)) were collected from each site (except for Cape Arago where 50 mussels were collected). Third, in 2001, quadrat surveys of drilled mussels were completed at a subset of the sites. The mussel shells from the 2008-2009 period were originally collected to survey predation in mussel beds (Sanford & Worth 2009). At each site, mussels from ten 0.25-square meter (m²) quadrats were removed, measured, and assessed for drill holes. For the mussel shells from 2019, approximately 100 live mussels were collected from each site. For all collections containing live mussels, the tissue was removed, and the shells were rinsed in fresh water and then air dried.

Mussel shells were cut on a bandsaw at 1/3 the length of the left valve from the anterior end. The mussel shell cross sections were scanned (model: CanoScan LiDE 110) and photos of the anterior section were used to calculate thickness via imaging software (ImageJ; Java 1.8.0_172). Maximum and minimum thickness along each cross section was measured, disregarding the dorsal hinge for maximum thickness and growing lip for minimum thickness, as these regions are known to be significantly thicker and thinner, respectively. Subsequently, average thickness was calculated using these two measurements. Due to the historical nature of the 2000-2001 and 2008-2009 mussel shells, there was some variation in how they were processed. First, some of the archived mussels were drilled/empty shells. Second, some of the 2008-2009 mussels only had the right valve remaining. Third, some of the 2000-2001 and 2008-2009 shells were analyzed on the posterior cross section since these shells were cut for a previous experiment and some shell pieces were missing.

We used the 2019 mussel shells to test the validity of our measurement of thickness to alternate metrics for shell thickness. For all 2019 shells, indirect shell thickness across the entire left valve was calculated as:

1000* valve dry weight / surface area

(where surface area = length x (height² + width²)^0.5 x pi/2) (Freeman & Byers 2006).

We also used 2019 mussels from two sites (Soberanes Point and Strawberry Hill) to determine the integrated thickness of the cross section, measured as the area of the polygon of the scanned image divided by the length of the curved mussel shell.

To control for the effect of mussel length on mussel shell thickness, we used the ratio of mean thickness at 1/3 the length of the mussel to mussel length as our response variable.

- Imported original file "M.californianus_shell_thickness_2000:01_2008:09_2019.xls" into the BCO-DMO system.
- Flagged 'NA' as a missing data value (missing values are blank/empty in the final file).
- Created Latitude and Longitude columns and added the values for each site as provided in the metadata.
- Converted the latitude and longitude values to decimal degrees and rounded to 5 decimal places.
- Renamed columns/fields to comply with BCO-DMO naming conventions.
- Rounded the 'Average_Thickness' column to 3 decimal places to match formatting that had been applied in the original Excel file.
- Rounded the 'Inegrated_Segment_Thickness' column to 3 decimal places.
- Saved the final file as "908647_v1_shell_thickness.csv".

NSF Award Abstract:
Historically, ecologists regarded evolution as a process that typically acts slowly over very long time scales. However, recent studies suggest that evolution might also shape the way species interact over much shorter timespans, ranging from weeks to years. Are these sorts of rapid feedbacks between evolution and ecology important in marine ecosystems? This project will address this question along the Pacific coast of the United States by studying predatory snails (Channeled Dogwhelks) that feed on California Mussels, an important habitat-forming species on rocky intertidal shores. Prior research shows that some dogwhelk populations are composed of an assortment of individuals that differ genetically in how effectively they can drill through mussel shells. This project will test whether short-term changes in the environment can impose rapid natural selection that favors some of these drilling variants over others, altering the effects that a dogwhelk population has on the surrounding mussel bed. At the same time, this project will examine whether regional differences in mussel shell thickness have influenced the evolution of drilling ability among dogwhelk populations distributed along >900 kilometers of the California and Oregon coasts. Overall, this study seeks to understand the dynamic feedbacks between evolution and ecology that might influence marine communities in the face of changing ocean conditions. This project will train diverse undergraduate and graduate students and will provide the foundation for a significant public outreach component, including the production of accessible video documentaries.

This project seeks to advance our understanding of eco-evolutionary dynamics in the sea by investigating links among oceanographic variation, natural selection, species interactions, and community succession. This project will use the interaction between the Channeled Dogwhelk (Nucella canaliculata) and the California Mussel (Mytilus californianus) as a model system to address two central objectives. (1) The research team will explore how spatial mosaics of selection drive adaptive differentiation among populations of consumers. Newly collected and archived mussels will be analyzed to characterize variation in shell thickness along the coasts of California and Oregon, and to evaluate whether this spatial mosaic has been consistent or variable over the past two decades. Laboratory experiments will test whether dogwhelk populations distributed across this mosaic have diverged in the thickness of shell that they can drill successfully. (2) The research team will examine whether temporal variation in selection on consumer phenotypes shapes predator-prey interactions, with cascading effects on ecological dynamics. In particular, the project will test whether short-term variation in prey recruitment and shell thickness can impose rapid selection on the frequency of drilling phenotypes within a dogwhelk population. A field experiment will also test whether selection on these predator phenotypes in turn alters the trajectory of mussel bed succession.

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.