To test the ecological consequences of phenotypic variation in dogwhelk drilling, Nucella canaliculata dogwhelks were outplanted to field cages and the effects on mussel bed succession were quantified as changes in percent cover of sessile species. In May of 2020, sixteen large plots of mid-intertidal mussel bed were cleared to bare rock at the Mussel Point site in Bodega Marine Reserve. The communities were left to naturally develop for a year until they were at a mid-successional stage. Stainless steel mesh cages with removable lids were then placed in the 16 areas in May of 2021. Cages were attached by bolting the cage to the rock and sealing the edges with marine epoxy (Z-spar splash zone compound). Cages were in a block design with 5 cages placed in the 16 areas. In July of 2021, 5 adult dogwhelks were placed in each cage. Cages within each block received dogwhelks from the same family (dogwhelks from the same egg capsule cluster were considered a family of snails), with each cage getting dogwhelks from a given early-life diet treatment, plus one was a reference cage that did not get any dogwhelks. Mussel bed succession in the cages was quantified approximately every eight weeks for the next year (a total of 7 experimental checks, plus one check before the outplant of dogwhelks). The lids of the cages were removed, and photographs were taken of each plot. These photos are in the attached Supplemental File "Percent Cover Images.zip". Percent cover of sessile species was quantified from the photographs using image analysis by tracing polygons around individuals of a given species and dividing the total area by the area of the caged plot. Species were grouped into seven functional groups for analyses: bare rock, acorn barnacles, gooseneck barnacles, mussels, other sessile animals, coralline algae, and a final group of algae and surfgrass.