Substrate limitation and environmental heterogeneity shape kelp habitat distribution in a complex coastal landscape

Understanding kelp forest distribution and the variables that constrain habitat suitability is critical for conservation and management. Habitat suitability models are especially valuable in complex coastal regions, such as fjord-archipelago systems, whose heterogeneous conditions can create a mosaic of continuous, patchy, and fringing kelp areas that are not well captured by satellite mapping. In this study, we (1) developed habitat suitability models for one such fjord-archipelago in British Columbia, Canada, to identify the potential suitable habitat distribution (PSHD; based on abiotic environmental conditions) and the actual suitable habitat distribution (ASHD; subset of the PSHD where substrate and depth are adequate) of canopy-forming kelps, and (2) evaluated the environmental and physical factors limiting ASHD. We found a wide kelp PSHD, covering both the archipelago and fjord areas of the region. Most areas within the PSHD were characterized by strong tidal and bottom currents and low surface and bottom temperatures, influenced by exchanges between major water bodies to the west and south. The ASHD represented 33% of PSHD, with rocky substrate and suitable depth reducing the PSHD by 33 and 34%, respectively. The predicted ASHD corresponded well with independent kelp presence records (81% accuracy). These findings provide a robust basis for kelp restoration and marine spatial planning in a heterogeneous, ecologically significant fjord-archipelago system, where local ocean warming has not yet exceeded the thermal tolerance of canopy-forming kelps.