Freshwater diatom communities from Ile Amsterdam (TAAF, southern Indian Ocean)

International audience; Diatom and water chemistry samples were collected during the austral summer of 2007 from lakes, streams and bogponds on Ile Amsterdam (TAAF), a small island located in the southern Indian Ocean. A diverse diatom flora of 104 taxa was found, dominated by several Pinnularia taxa, Frustulia lebouvieri, Kobayasiella subantarctica, Eunotia paludosa, E. muscicola and Planothidium subantarcticum. Biogeographically, the Ile Amsterdam freshwater diatom flora is composed of cosmopolitan, sub-Antarctic and endemic elements. The biogeographical analysis showed that almost 17% of all observed taxa can be considered endemic to Ile Amsterdam with an additional 14% showing an exclusive sub-Antarctic distribution. The flora can be considered as typical for oceanic islands based on its disharmonic composition with several genera lacking and other being overrepresented. Canonical Component Analysis was used to classify the samples based on their chemical characteristics, revealing that, specific conductance, sulphate and pH were the main factors dividing the samples into four different groups. The geological history of the island in combination with the climate and the specific environmental features of the main habitat in the Caldera most likely shaped the composition of the actual diatom communities.