Modeling of the geographical distribution of two forest-forming fucoids in the Strait-Alboran demarcation (southern Iberian Peninsula): Implications for conservation and restoration.

Marine forests formed by canopy-forming brown algae of the former Cystoseira complex are key habitat-forming components of Mediterranean coastal ecosystems, supporting biodiversity and multiple ecosystem functions. However, many populations have declined in recent decades due to increasing anthropogenic pressures and climate change, raising concerns about the persistence of these foundational species. Identifying the environmental drivers that shape their distribution is therefore essential for predicting future changes and guiding conservation actions. Here, we applied species distribution models to evaluate the environmental determinants, present habitat suitability, and potential future distribution of two emblematic fucoid species, Gongolaria usneoides and Ericaria selaginoides, in the Strait of Gibraltar-Alboran Sea region, a major Mediterranean biodiversity hotspot and climatic transition zone. Present-day models were projected to the end of the century under two contrasting climate scenarios (SSP1-1.9 and SSP5-8.5). Mixed layer depth was the dominant predictor structuring species distributions, highlighting the role of water column stratification and hydrographic dynamics in regulating benthic habitats. The two species exhibited contrasting responses: Gongolaria usneoides occupied a narrow environmental niche and showed spatially heterogeneous future responses, including localized suitability increases around the Strait of Gibraltar and western Alboran sectors together with suitability declines across portions of the eastern coastline under both climate scenarios. In contrast, Ericaria selaginoides showed broader environmental tolerance and generally positive, although spatially heterogeneous, suitability responses across large portions of the region. These results suggest that future environmental change may restructure Mediterranean marine forests through species-specific responses rather than through uniform decline.