Multi-scale interactions between local hydrography, seabed topography, and community assembly on cold-water coral reefs

Abstract. We investigated how the interactive effects of hydrography, topography and intrinsic community dynamics influence the assembly of species and functional traits across multiple spatial scales of a cold-water coral reef seascape. In a novel approach for these ecosystems, we use a spatially resolved complex three-dimensional flow model of hydrography to help explain assembly patterns. Forward selection of distance-based Moran's eigenvector mapping (dbMEM) variables identified two submodels of spatial scales at which communities are structured: broad-scale (across reef) and fine-scale (within reef). Canonical variance partitioning revealed broad-scale structures created mainly by variability in bathymetry and hydrography across reefs, which manifest as relatively narrow environmental niches for predators and scavenging detritivores. Fine-scale assembly was related more to processes that create spatially autocorrelated patches of fauna within a reef due to restricted dispersal in sessile fauna but social mating interactions and food supply in more mobile organisms. Our study implies that perturbations such as habitat fragmentation and altered hydrodynamic regimes have the potential to induce significant changes in the structure and function of cold-water coral reef ecosystems at spatial scales that span the entire seascape.