Supplementary Figure S5. Jackknife tests of variable importance for the coralligenous outcrops distribution model: (a) test gain, (b) test AUC. cora: coralligenous outcrops. See Table 3 for full names of environmental variables. Supplementary Figure S6. Jackknife tests of variable importance for the maërl beds distribution model: (a) test gain, (b) test AUC. See Table 3 for full names of environmental variables. Supplementary Table S1. Variables considered for use as input into the models. A subset (12 variables) was selected () for model development. Name Source development Bathymetry EMODNet Hydrography Portal  Bottom salinity World Ocean Database 2009  Bottom temperature World Ocean Database 200961  Bottom type Halpern et al., 2008  Chlorophyll a concentration Tyberghein et al., 2012 Diffuse attenuation coefficient Tyberghein et al., 2012 Distance to ports Port location from World Port Index 2011  Distance to (major) river mouths River mouth location from ESRI Data and Maps (2012) and 
Wessel and Smith (1996) Euphotic depth Ocean Color Web  Geostrophic velocities of sea surface current Aviso SSALTO/DUACS  Nutrient input Halpern et al., 2008  Phosphate concentration Tyberghein et al., 2012  Pollutants (inorganic) Halpern et al., 2008 Pollutants (organic) Halpern et al., 2008 Sea Surface Temperature Tyberghein et al., 2012 Silicate concentration Tyberghein et al., 2012  of the seafloor Based on bathymetry layer of EMODNet Hydrography Portal  Supplementary S2. Georeferenced occurrence data on coralligenous outcrops and maërl beds, as collated for each country bordering the Mediterranean Sea. Sampling intensity being very uneven across the different countries, the numbers of points/lines/polygons are unrelated to the actual surface areas covered by these habitats. For instance, the high numbers for Malta and France (Corsica) result from two high-resolution surveys that took place northwest and east of Malta and north of Corsica. Nevertheless, the information in this table reflects the unprecedented extent of the collated datasets for coralligenous outcrops and maërl beds in the Mediterranean Sea. Coralligenous outcrops Maërl beds Total Point Line Polygon Point Polygon Country Albania 0 0 4 0 0 4 Algeria 10 0 7 0 0 17
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