Mussel bed community data for: Intraspecific variation in a marine predator changes intertidal community through effects on a foundation species

Intraspecific variation is an important form of biodiversity that can alter community and ecosystem properties. Recent work demonstrates the community effects of intraspecific variation in predators via altering prey communities and in foundation species via shaping habitat attributes. However, tests of the community effects of intraspecific trait variation in predators acting on foundation species are lacking despite the fact that consumption of foundation species can have strong community effects by shaping habitat structure. Here we tested the hypothesis that intraspecific foraging differences among populations of mussel-drilling dogwhelk predators (Nucella) differentially alter intertidal communities through effects on foundational mussels. We conducted a nine-month field experiment where we exposed intertidal mussel bed communities to predation from three Nucella populations that exhibit differences in size-selectivity and consumption time for mussel prey. At the end of the experiment, we measured mussel bed structure, species diversity, and community composition. While exposure to Nucella originating from different populations did not significantly alter overall community diversity, we found that differences in Nucella mussel selectivity significantly altered foundational mussel bed structure, which in turn altered the biomass of shore crabs and periwinkle snails. Our study extends the emerging paradigm of the ecological importance of intraspecific variation to include the effects of intraspecific variation in predators of foundation species.

Methods
The dataset was collected after the completion of a nine-month intertidal mussel bed experiment in the mid-intertidal zone testing the effects of intraspecific variation in dogwhelk predators in the genus Nucella. In the experiment, there were 32 plastic Vexar mesh intertidal cages bolted to a relatively flat area of rock, and each contained California mussel bed communities. The cages were treated with dogwhelk predators from three different populations. The goal was to test the effects of differential predation by the dogwhelk populations on the mussel bed physical structure and ecological community. At the completion of the experiment, each cage was photographed from above. Then, the entire community in each cage was removed by hand and frozen for later analysis. The frozen samples were then sorted by species (or as close as we could get to species), classified, weighed, and measured by hand in a laboratory. Dogwhelk data refers to the populations, sizes, and masses of dogwhelk predators used as treatments in the cages. Drilled mussel data refers to the sizes of mussels found with at least one drill hole by the end of the experiment. Remaining mussel data refers to the sizes of mussels found still alive at the end of the experiment. Community data refers to the identification and mass (except algae, which is measured in percent cover instead of mass) of all organisms living in the mussel beds at the end of the experiment.