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

Aim: Climate change affects dramatically biogenic habitats by altering the geographic distribution of the foundational speciesand the structure of landscapes they form. As a consequence, the associated biotic communities could experience habitat lossand fragmentation. In this paper, we assess how climate change impacts the geographic distribution of Mediterranean seagrasshabitats 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 distri-bution in the present climate using Species Distribution Models (SDMs). Based on the identified habitat configuration, we employa neutral metacommunity model (NMM) to simulate virtual metacommunities structured by stochastic demographic processesand dispersal.Results: SDMs were fitted with acceptable performances. We show a strong range contraction for both seagrass species (withuncertain predictions for the Southern and Eastern Mediterranean), a decrease in alpha diversity of associated communities, andan increase in beta diversity at the Mediterranean scale. Such changes are solely the result of the rearrangement of the landscapecaused by climate change and create an offset for any distributional change related to niche effects. For different basins, we showthat patterns of alpha diversity under realistic species dispersal are strongly correlated with habitat availability, while beta diver-sity 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 beuseful for planning conservation and restoration measures at local and regional scales. We show that, besides niche effects, cli -mate change can impact species distribution by altering the landscape structure