We collected Pisaster ochraceus along the coastline of Carmet Beach, California (38.372172 N, 123.076438 W) in spring of 2018, and Nucella lamellosa at Washington Park in Anacortes, Washington (48.502190 N, -122.691865 W) in July 2018.

We placed 20 Nucella in each of ten containers (33cm x 20cm x 11.5cm) for a total of 200 individuals (25.9mm +/- 2.4mm in length). Half of the containers were supplied with seawater flowing from a chamber above them that held one Pisaster (96.7mm +/- 8.5mm from madreporite to longest arm). This set of containers resulted in morphologically induced snails, where individuals retracted their bodies farther into their shells, potentially from an elongation of shell length (Bourdeau 2009). The other five containers were supplied from a chamber with just seawater (no sea star cue) flowing from it, resulting in non-induced snails. All the Nucella during the experiment were fed ad libitum with Balanus barnacle prey.

We measured various Nucella morphometrics at multiple time points of the experiment. The morphometrics include Nucella weight, the length of the shell from the apex to the notch, the height of the shell from the base of the aperture to the top of the shell, and the retraction capability of Nucella. Retraction into the shell is our focal metric and is defined as the distance from the base of the snail’s aperture by the columella to its operculum when the individual is fully retracted. The induction (or non-induction) period lasted from July 2, 2018 to November 14, 2018. Further morphometric data were collected in February 2019 but were not used in the analysis.

To test the effect of predator cue on Nucella morphology, we analyzed whether there was an effect of Pisaster cue on retractability both at the start and end of the induction period. Both containers and individual Nucella were included as random effects.

Organism identifiers (taxonomic names used in dataset metadata):
Scientific Name, Life Science Identifier (LSID)
Nucella lamellosa, urn:lsid:marinespecies.org:taxname:404218
Pisaster ochraceus,urn:lsid:marinespecies.org:taxname:240755