Global biodiversity and biogeography of rhodolith-forming species

Unattached nodules of calcareous red algae (Rhodophyta), known as rhodoliths, are widely reported and studied in places that extend from the tropics to polar latitudes. Factors controlling distribution rhodolith-forming species remain poorly understood. A review global present-day rhodolith beds was undertaken, collating information on 106 10 families, representing 21 genera distributed through 11 realms: 1) Arctic, 2) Temperate Northern Atlantic, 3) Pacific, 4) Tropical 5) Western Indo-Pacific, 6) Central 7) Eastern 8) 9) South America, 10) Australasia, 11) Southern Ocean. The Indo-Pacific Australasia proved be most diverse realms. Of 62 provinces across these realms, Southwestern Mediterranean Sea East Pacific feature highest diversity species. significant proportion (14.2%; 15 species) endemic a single biogeographic province. Species richness is weakly related sampling effort (r2=0.573) unrelated littoral area (r2=0.012). Even when high latitude excluded analysis, no correlation between found (r2 = 0.0005). wider, evolutionary-time framework revealed existence marine barriers geological age their final emplacement key elements explaining compositional differences rhodoliths former contiguous areas (e.g., versus Atlantic shores Panama Costa Rica, America; eastern Red Gulf Aden). Finally, we propose lower tropical Ocean compared (23 33 spp.), may linked higher abundance corals coral reefs which act competitors with coralline for space.