Kelp forests provide key habitat on the Pacific Coast of Canada; however, the long-term changes in their distribution and abundance remain poorly understood. With advances in satellite technology, floating kelp forests can now be monitored across large-scale areas. We present a methodological framework using an object-based image analysis approach that enables the combination of imagery from multiple satellites at different spatial resolutions and temporal coverage, to map kelp forests with floating canopy through time. The framework comprises four steps: (1) compilation and quality assessment; (2) preprocessing; (3) an object-oriented classification; and (4) an accuracy assessment. Additionally, the impact of spatial resolution on the detectability of floating kelp forests is described. Overall, this workflow was successful in producing accurate maps of floating kelp forests, with global accuracy scores of between 88% and 94%. When comparing the impact of resolution on detectability, lower resolutions were less reliable at detecting small kelp forests in high slope areas. Based on the analysis, we suggest removing high slope areas (11.4%) from time series analyses using high- to medium-resolution satellite imagery and that error, in this case up to 7%, be considered when comparing imagery at different resolutions in low–mid slope areas through time.

Aim: We review the past, present and future biogeography of kelps (Order Laminariales), integrating recent advances in phylogeography, population genomics and species distribution modelling to outline the key patterns and processes relevant to kelp biogeography. Location: Global. Taxa: Kelp (Order Laminariales). Methods: We synthesized recent research on the biogeography of kelps, spanning molecular phylogeography to studies aimed at inferring future species distributions. Using this information, we reconstruct past dispersal pathways that kelp species took across ancient oceans, present patterns in kelp biogeography and summarize the changes in kelp diversity and distributions that are expected by the end of the 21st century. Results: Kelps originated in the North Pacific ~30–35 Ma, which remains the global centre of kelp species diversity. Kelps then dispersed globally via two primary routes: northward through the Bering Strait into the Arctic and Atlantic Oceans, and southward across the equator into the Southern Hemisphere through at least five or six independent trans‐equatorial dispersal events. Modern biogeographic patterns have been altered by large‐scale climatic impacts, as well as human‐mediated species introductions. Future projections indicate continued impacts of climate change on the distribution of kelp species. In particular, we expect species richness to increase at high latitudes and decrease at lower latitudes, depending on the availability of coastline. Main Conclusions: The global distribution of kelps reflects a complex history of evolutionary diversification, climate change and human influence that continues to reshape the biogeographic distribution of contemporary species. Integrating phylogeographic information, ecological observations and evidence from distribution modelling reveals that kelp biogeography has and will continue to be dynamic through time, providing a powerful case study for understanding how marine foundation species respond to past and future environmental change.