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RESEARCH PRODUCT

Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean.

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ABSTRACTAim Biogeographical patterns within three classes, the Echinoidea, Bivalvia andGastropoda, were investigated in Antarctic, sub-Antarctic and cold-temperateareas based on species occurrence data. Faunal similarities among regions wereanalysed to: (1) test the robustness of the biogeographical patterns previouslyidentified in bivalves and gastropods; (2) compare them with the biogeographi-cal patterns identified for echinoids; and (3) evaluate the reliability of the bio-geographical provinces previously proposed, depending on the taxa andtaxonomic levels analysed.Location The Southern Ocean, sub-Antarctic islands and cold-temperate areassouth of 45° S latitude at depths of < 1000 m.Methods Taxonomic similarities among 14 bioregions were analysed using anon-hierarchical clustering method, the bootstrapped spanning network (BSN)procedure. Taxonomic similarities were analysed within the three classes at spe-cies and genus levels.Results The previously identified large-scale biogeographical entities are clari-fied. Echinoid and bivalve faunas are structured mainly according to three fau-nal provinces: (1) New Zealand, (2) southern South America and sub-Antarcticislands, and (3) Antarctica. Gastropod faunas group into five provinces:(1) New Zealand, (2) southern South America, (3) east sub-Antarctic islands,(4) West Antarctica, and (5) East Antarctica. Strong faunal relationshipsbetween bioregions perfectly match the flows of the Antarctic Circumpolar andAntarctic Coastal currents. Moreover, the legacy of the climatic and palaeoceano-graphic history of Antarctica is revealed by trans-Antarctic faunal affinities,thereby strongly supporting hypotheses of past marine seaways that would haveconnected both the Amundsen–Bellingshausen area to the Weddell Sea and theWeddell Sea to the Ross Sea.Main conclusions A significant advantage of the BSN procedure lies in thepossibility of identifying both biogeographical groupings and transitional areas;that is, both strong connections and groupings between bioregions. Themethod has also proved to be efficient for identifying potential faunal exchangepathways and dispersal routes, both present and past, by fitting networks tooceanographic and palaeogeographical maps.KeywordsAntarctic, bootstrapped spanning network, dispersal, sub-Antarctic, trans-Antarctic seaway, vicariance.1374