Giant kelp forests are some of the most productive and biodiverse ecosystems in the world, but they are vulnerable to stressors associated with global climate change. As a foundation species, giant kelp (Macrocystis pyrifera) provides habitat, food, and refuge for hundreds of species, many of which are economically important. Much of what is known about giant kelp is focused on the adult stage and the abiotic factors influencing the persistence and recovery of this species. However, under increasing environmental variability, it is critical to understand the factors impacting the survival of juvenile kelp, which has direct implications for the success of the adults. One of the largest gaps in our knowledge of giant kelp forests is the role of a diversity of grazers on the early life stages of M. pyrifera, and virtually nothing is known about the impacts of climate change on these species interactions. In this dissertation, I use both laboratory and field experiments to quantify the impacts of four grazers on two life stages of juvenile kelp under ocean acidification and hypoxia. I found that grazers are a significant source of mortality on juvenile kelp, and that an often overlooked herbivore in the literature, the brown turban snail, emerges as a dominant grazer on both microscopic and macroscopic stages. Under climate change, consumption is significantly reduced, increasing estimated kelp survival, and hypoxia drives these decreases in consumption across all four grazing species. By utilizing natural variability regimes within an upwelling season, I found through field experiments that grazing rates decreased with high monthly oxygen variance, suggesting that cumulative impacts of more extreme conditions may also impact herbivore feeding behavior. Overall, the results of this dissertation demonstrate that herbivory can play a significant role influencing the persistence of giant kelp, and that under the threat of climate change, these species interactions will be significantly weakened, which has implications for kelp forest ecosystems and the transfer of primary productivity through these diverse food webs. This dissertation provides critical information on the ecology and persistence of giant kelp forests and gives us a greater understanding of climate change impacts on marine communities.