Scaling-Up Biodiversity-Ecosystem Functioning Relationships: Using Rocky Shores as a Model SystemMacroecology

Tom Fairchild¹, John Griffin¹, Pippa Moore², Dan Smale³, Mike Burrows⁴, Lars Gamfeldt⁵, Jon Lefcheck⁶, Andrew Gonzales⁷, Benedikt Brunner⁵, Luis Depablo⁸, Mike Fowler¹, Joshua Mutter¹

¹Swansea University, UK - ²Newcastle University, UK - ³The Marine Biological Association of the UK, UK - ⁴Scottish Association of Marine Sciences, UK - ⁵University of Gothenburg, Sweden - ⁶University of Maryland, USA - ⁷McGill University, Canada - ⁸University of Colorado Boulder, USA

Small-scale experiments demonstrate that biodiversity underpins ecosystem functioning, but how these relationships scale to land- or seascapes remains poorly understood. Theory predicts that as environmental heterogeneity increases with spatial scale, so does biodiversity’s role, as diverse species are needed to fill varied niches. Using rockweed- and kelp-dominated rocky shores (“intertidal forests”) across Great Britain—spanning gradients in shore height, wave exposure, and latitude—as a model system, we tested these predictions. Field surveys at 25 sites revealed that rockweed and kelp richness–biomass relationships strengthened with increasing spatial scale and heterogeneity. To move beyond correlations, we used species distribution models to simulate species loss alongside compensatory responses of remaining species. Simulations confirmed that biodiversity loss reduces biomass most strongly at larger scales, even when compensation occurs. A dynamic meta-community model further explored drivers of scale dependence in BEF relationships, emphasizing the roles of niche differentiation, connectivity, and compensatory capacity. Our findings show that at small scales with low environmental heterogeneity, few species are needed to maximize functioning, and species identity is critical. Conversely, at larger scales with greater environmental variability, biodiversity’s influence grows, requiring diverse species to fill varied niches. These results underscore the importance of seaweed biodiversity on rocky reefs and warn against extrapolating small-scale BEF studies to broader scales, where ecosystem services are delivered and management decisions are made.