Landscape‐Mediated Effects of Climate Change on Metacommunities Inhabiting Mediterranean Seagrass

ABSTRACT Aim Climate change affects dramatically biogenic habitats by altering the geographic distribution of the foundational species and the structure of landscapes they form. As a consequence, the associated biotic communities could experience habitat loss and fragmentation. In this paper, we assess how climate change impacts the geographic distribution of Mediterranean seagrass habitats and the cascading effects on the biodiversity of metacommunities they support. Location Mediterranean Sea. Taxon Posidonia oceanica and Cymodocea nodosa. Methods We employ state‐of‐the‐art physical and biogeochemical data for the Mediterranean Sea to model the seagrass distribution in the present climate using Species Distribution Models (SDMs). Based on the identified habitat configuration, we employ a neutral metacommunity model (NMM) to simulate virtual metacommunities structured by stochastic demographic processes and dispersal. Results SDMs were fitted with acceptable performances. We show a strong range contraction for both seagrass species (with uncertain predictions for the Southern and Eastern Mediterranean), a decrease in alpha diversity of associated communities, and an increase in beta diversity at the Mediterranean scale. Such changes are solely the result of the rearrangement of the landscape caused by climate change and create an offset for any distributional change related to niche effects. For different basins, we show that patterns of alpha diversity under realistic species dispersal are strongly correlated with habitat availability, while beta diversity is largely influenced by the changes in the spatial configuration of seagrass habitats. Main Conclusions By highlighting hotspots of metacommunity change linked to habitat fragmentation, our method can be useful for planning conservation and restoration measures at local and regional scales. We show that, besides niche effects, climate change can impact species distribution by altering the landscape structure.