Dataset: Algal consumption data from Tegula in the presence of the predator Pisaster ochraceus, displaying anti-predatory responses or not within mesocosms at Bodega Marine Lab in 2018.

To examine the impacts of fear removal on the strength of trophic cascades, we measured the amount of algae (Ulva spp.) consumed by Tegula funebralis that displayed either an anti-predatory response to its predators, Pisaster ochraceus and Cancer productus, or ignored the predators. Additionally, we used two species of predators with differing consumption rates to test how predator traits might mediate the effect of removal on trophic cascade strength. The experiment was conducted within laboratory mesocosms at Bodega Marine Lab in 2018.

Pisaster ochraceus, Cancer productus, and Tegula funebralis were collected along the coastline of Sonoma County, California in 2018. Both Pisaster and Tegula were sampled at Carmet Beach (38.372172 N, -123.076438 W), and the Cancer crabs were gathered subtidally from Doran Beach (38.309334 N, -123.048703 W).

When conducting the fear and no-fear treatments for Tegula, we had 20 mesocosms with ten Tegula each when paired with Pisaster as the predator. Ten of the mesocosms were used for the fear treatment where we introduced Pisaster cues from a secondary container to provoke a behavioral fear response in Tegula. The other ten mesocosms contained no Pisaster cues and represented the no-fear treatment. In the fear treatment, we culled Tegula at the baseline rate of 8% per day, and we culled Tegula at the enhanced rate of 33% per day in the no-fear treatment.  Ulva sp. was used as the basal resource with Tegula, and we measured the change in Ulva weight over the duration of the experiment. We dried the Ulva for two hours before weighing them. We also had ten mesocosms with just seawater and Ulva as a control to measure the natural degradation of Ulva over the course of the experiment.

We conducted similar fear and no-fear treatments with Tegula except paired with Cancer as the predator. The contrast in the effect of fear on the trophic cascades between the two predators shows how predators of differing dangerousness can influence the role of fear in trophic cascades. Like the Pisaster-Tegula experiments, we used 20 mesocosms with ten Tegula each for the Cancer-Tegula experiments. We used ten of those mesocosms for the fear treatment where Cancer cues are introduced to provoke a behavioral fear response and used the remaining ten mesocosms for the no-fear treatment. In the fear treatment, Tegula were culled at the baseline rate of 34% per day, and in the no-fear treatment, Tegula were culled at the enhanced rate of 57% per day, simulating Cancer predation rates.

To analyze the role of fear and predator identity on amount of algae consumed by Tegula, we ran a generalized linear model with a gamma distribution to account for the heteroscedasticity in the amount of algae consumed. Predator identity and the presence of fear were used as fixed effects. We followed up each generalized linear mixed effects model with explicit a priori planned contrasts with either a Bonferroni or Tukey correction. For Tegula, we compared whether afraid snails consumed significantly different amounts of algae for each predator and whether that difference was different between predators.

Organism identifiers:

Scientific Name, Life Science Identifier (LSID)
Pisaster ochraceus,urn:lsid:marinespecies.org:taxname:240755
Cancer productus,urn:lsid:marinespecies.org:taxname:440382
Ulva spp.,urn:lsid:marinespecies.org:taxname:144296
Tegula funebralis, urn:lsid:marinespecies.org:taxname:534190