Biodiversity and biogeography of hydroids across marine ecoregions and provinces of southern South America and Antarctica

Abstract

To better understand the biodiversity-biogeographic polar connections between southern South America and Antarctica (SSA & A), we used benthic communities of hydroids as a model to investigate marine assemblages by evaluating classic spatial divisions at diferent geographical resolutions. Using a georeferenced dataset of 249 species and multivariate analyses, we investigated species’ distribution, composition and biogeographic connectivity, and defned assemblages of ecoregions and provinces for the area. Hotspots of rich biodiversity at risk of depletion were defned. Analyses of ecoregions have a more stratifed biogeographic structure, and reveal critical regions susceptible to loss of diversity. Analyses of provinces show a clear division between Atlantic-Pacifc and Antarctic-Subantartic assemblages, with high biogeographic isolation of the Subantarctic islands. Depending on spatial resolution, the biogeographic position of the Magellan area is spatially contradictory, clustering on the one hand with SSA ecoregions and on the other with Antarctic provinces. Our patterns appear to be driven by diferent combinations of processes and barriers, refected in the stratifed distribution of hydroids. The high level of endemism and concentration of species at the edge of distribution in the Magellan area and Scotia Arc suggest their transitional nature and particular importance for understanding the historical and ecological connections between SSA & A.