Comparative biogeography of echinoids, bivalves and gastropods from the Southern Ocean
Correspondence: Benjamin Pierrat, Biogéosciences, UMR CNRS 6282, Université de Bourgogne, 6 boulevard Gabriel, 21000 Dijon, France.
Biogeographical patterns within three classes, the Echinoidea, Bivalvia and Gastropoda, were investigated in Antarctic, sub-Antarctic and cold-temperate areas based on species occurrence data. Faunal similarities among regions were analysed to: (1) test the robustness of the biogeographical patterns previously identified in bivalves and gastropods; (2) compare them with the biogeographical patterns identified for echinoids; and (3) evaluate the reliability of the biogeographical provinces previously proposed, depending on the taxa and taxonomic levels analysed.
The Southern Ocean, sub-Antarctic islands and cold-temperate areas south of 45° S latitude at depths of < 1000 m.
Taxonomic similarities among 14 bioregions were analysed using a non-hierarchical clustering method, the bootstrapped spanning network (BSN) procedure. Taxonomic similarities were analysed within the three classes at species and genus levels.
The previously identified large-scale biogeographical entities are clarified. Echinoid and bivalve faunas are structured mainly according to three faunal provinces: (1) New Zealand, (2) southern South America and sub-Antarctic islands, 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 relationships between bioregions perfectly match the flows of the Antarctic Circumpolar and Antarctic Coastal currents. Moreover, the legacy of the climatic and palaeoceanographic history of Antarctica is revealed by trans-Antarctic faunal affinities, thereby strongly supporting hypotheses of past marine seaways that would have connected both the Amundsen–Bellingshausen area to the Weddell Sea and the Weddell Sea to the Ross Sea.
A significant advantage of the BSN procedure lies in the possibility of identifying both biogeographical groupings and transitional areas; that is, both strong connections and groupings between bioregions. The method has also proved to be efficient for identifying potential faunal exchange pathways and dispersal routes, both present and past, by fitting networks to oceanographic and palaeogeographical maps.