Freshwater diatoms form Ile de la Possession (Crozet Archipelago, sub-Antarctica): an ecological assessment

An ecological study of freshwater waterbodies on Ile de la Possession (Croz et Archipelago, Antarctica) was undertaken during the austral summer of 199 7/ 1998. Both diatom and chemistry data were collected. A highly diverse di atom flora of 210 taxa, belonging to 32 genera, was identified from 127 sam ples. The most abundant genera were Fragilaria, Achnanthes and Navicula. Pr incipal Component Analysis was used to classify the samples on the basis of their chemical characteristics. The analysis revealed that pH and chloride were the main factors dividing the samples into three categories: rivers, more acid lakes, and lakes with higher chloride content. Species assemblage s correspond well with this division. Forward selection with Monte Carlo pe rmutations selected pH, chloride, habitat and hardness. Based on the analys is, four groups of samples can be made: rivers, acid lakes, circumneutral l akes with low chloride concentrations and coastal pools with relatively hig h chloride levels. The results also indicate that a specific diatom flora e xists on the island, which is comparable to that of other islands in the sa me area (Kerguelen and Macquarie).