Ecologists have long sought to understand the relative importance of wide variety of physical and biological factors shaping aquatic communities. Kelp forests on the Pacific coast of North American have served as an ideal model system for examining the community level consequences of both top-down trophic cascades and bottom-up effects of nutrient availability, recruitment, and physical stress. Here we use structural equation modeling (SEM) to explore a data set describing the distributions and abundances of multiple taxa and the corresponding oceanographic conditions across 16 sites around the Channel Islands National Park in southern California over nearly twenty years. We examine the effects of adding increasing biological detail to our models, and consider how SEM can be applied to long-term observational field data. We show that multiple factors contribute to the structure of kelp forest food webs, and that patterns within the data match results from previous experimental studies that have examined each factor independently.