Coralline red algae of Antarctica and Subantarctic regions: state of knowledge of a threatened, yet poorly known, group of ecosystem engineers

Due to limitations imposed by the extreme environmental conditions, Antarctica and Subantarctic regions remain among the least phycologically known. Corallines of these regions are poorly known, despite a long history of studies dating back to the early twentieth century. Current knowledge of their diversity is based mostly on traditional morpho-anatomical investigations. For Antarctica proper, reliable records are available for 12 species; most of these are based on collections from intertidal and shallow subtidal habitats, with Leptophytum coulmanicum and L. foecundum being the most frequently reported. However, recent collections made in the deep subtidal of the Ross Sea and studied by a combination of morpho-anatomical and molecular data produced the discovery of the new genera and species Tethysphytum antarcticum and Thalassolithon adeliense; these represented two previously unknown lineages within the order Hapalidiales. Molecular data suggest that Thalassolithon has probably a much wider distribution, extending to the Auckland Islands and New Zealand. While 11 species of corallines are recognized based on molecular data from the Balleny Islands and the New Zealand subantarctic islands, only 5 of these can currently be assigned to genera. Four of them are confined to the Ross Sea/Balleny Islands or subantarctic islands, while the remainder have much wider distributions to Rakiura/Stewart Island and the New Zealand mainland. These discoveries confirm that the knowledge of coralline diversity in the Southern Ocean is largely incomplete. Further collections from presently unexplored regions and use of DNA sequence data, including sequences obtained from relevant type specimens, are key requirements for future progress.