Abundance-based distribution modelling reveals climate-driven loss of functionally important kelp forest habitat

Kelp forests are globally distributed foundational habitats that support coastal biodiversity and underpin key ecosystem services. Kelp taxa are vulnerable to climate-driven environmental change and major shifts at their range edges are expected, yet it remains unclear how populations will respond towards the centre of their distributions. We applied species distribution models using semi-quantitative density records of Laminaria hyperborea (Gunnerus) Foslie (Laminariaceae) to estimate current and future distributions of high-density habitat. Our analysis centred on the British Isles, a major portion of the global range of this species and an effective test-bed for assessing climate impacts on cool-temperate kelp forests. Under future climate scenarios for the year 2100, we projected declines of 55-59% in intermediate-density kelp park and losses of 76-91% in high-density kelp forest, highlighting the disproportionate vulnerability of dense structural habitats and associated ecosystem services, even where species occurrence is largely maintained. These results suggest that incorporating abundance into species distribution models is important for forecasting ecological impacts of climate change, since substantial reductions in habitat quality and function can precede detectable shifts in occurrence. Despite declines, spatial predictions also revealed extensive areas of suitable park and forest habitat even under future scenarios, highlighting opportunities for targeted restoration and afforestation which could improve population resilience and connectivity. More broadly, this work advances projections for an ecologically and economically important kelp species and provides a transferable framework for identifying functionally relevant climate refugia which can be extended to other kelp taxa and foundational habitats to better understand potential community reorganisation. This will inform conservation priorities and support strategies to safeguard coastal foundational ecosystems under global change.