Rafting dispersal in a brooding southern sea star (Asteroidea : Anasterias)

Marine biogeographers have long speculated that macroalgal rafting presents a dispersal mechanism for brooding marine invertebrates of the Southern Ocean, but few direct observations of rafting by echinoderm taxa have been documented. Here we report rafting of the brooding benthic sea star Anasterias suteri, along with two mollusc taxa (Onithochiton neglectus-also a brooder-and Cantharidus roseus), on detached bull-kelp Durvillaea antarctica in Foveaux Strait, southern New Zealand. The rafting journey, intercepted at sea, likely lasted for 2-3 weeks and may have covered several hundred kilometres. We use DNA sequences, together with meteorological and prevailing oceanographic data, to infer the likely Fiordland (mainland) origins of the raft and its epifauna. This rafting dispersal mechanism provides an explanation for the broad (circum-subantarctic) but disjunct distribution of brooding Anasterias populations, and for the genetic connectivity observed between their populations.