The Stress Gradient Hypothesis (SGH) predicts primary producer competition and facilitation is related to environmental stress. Despite being well-documented in terrestrial systems, facilitation is rarely integrated into our understanding of the dynamics in marine forests. Critical coastal habitats created by canopy-forming seaweeds have recently been seen to transition to less biodiverse regimes dominated by turf algae and populations are predicted to increasingly transition based on the paradigm that turf algae negatively affect canopy seaweeds. Meta-analysis was used to estimate the effect of turfs on canopy species using experimental and observational data. We found that turf species do compete with marine canopies in subtidal kelp forests, however, these interactions become increasingly facilitative at shallower depths and high latitude, supporting the SGH. This work provides new insight into the dynamics of a highly-studied ecosystem, and emphasizes the need to re-assess the importance of facilitation when predicting the response of systems to global change.