Topographic heterogeneity triggers multiple complementary cascades to exert cornerstone effects on ecosystem multifunctionality

Topographic heterogeneity sets the stage for community assembly, but its effects on ecosystem functioning remain poorly understood. Here we test the hypothesis that heterogeneity underpins multiple cascading pathways that indirectly control multifunctionality. To do so, we combined experimental manipulation of topographic heterogeneity on rocky shores with comprehensive assessment of naturally assembled communities and multifunctionality. Structural equation modelling revealed that heterogeneity: i) enhanced biodiversity by supporting filter feeder richness; ii) triggered a facilitation cascade via reef-forming (polycheate) and biomass-dominant (macroalga) foundation species, which in turn broadly supported functionally diverse epibiotic and understory assemblages; and iii) inhibited a key consumer (limpet). These mechanisms exerted complementary positive effects on individual functions (e.g., water filtration, ecosystem metabolism, nutrient uptake) and, in turn, collectively enhanced multifunctionality. Topographic heterogeneity may therefore serve as a cornerstone physical attribute by initiating multiple cascades that propagate through ecological communities via foundation species, ultimately manifesting disproportionate effects on ecosystem multifunctionality.