Biogeographic Processes Influencing Antarctic and sub-Antarctic Seaweeds

Antarctica has long been seen as biologically isolated, surrounded by the vast Southern Ocean and its circumpolar oceanographic currents and fronts and home to many endemic species. New evidence demonstrates, however, that buoyant seaweeds can cross perceived oceanographic barriers in the Southern Ocean to reach Antarctic coasts. These macroalgal rafts can carry diverse passengers, including marine invertebrates and other, non-buoyant seaweeds. The stark differences between Antarctic and sub-Antarctic near-coastal ecosystems are therefore more probably the result of environmental differences than physical isolation. Modelling indicates that algal rafts from the sub-Antarctic could reach Antarctic coasts every month, providing an ongoing influx of marine propagules that are poised to colonise as the climate warms. In this chapter, we review the following: (i) the evidence for the isolation of Antarctica, (ii) the oceanographic processes that can hinder or promote passive dispersal into Antarctic waters and (iii) the characteristics of organisms that could be rafting to Antarctic coasts with buoyant macroalgae.