On the factors affecting distributions of freshwater diatom species in a remote South Atlantic archipelago

Diatom species distributions on remote islands are influenced by both habitat quality and location. In this study diatom distributions and water quality were explored in the Falkland Islands archipelago with reference to island floras elsewhere, using 28 freshwater sites (small ponds, shallow lowland lakes, upland tarns and several streams). Site water chemistries varied from strongly acid to circum-neutral and from low to high conductivity and water-colour. Dissolved ions co-varied with conductivity and varied strongly between sites and ion ratios indicated a strong influence of sea-salt deposition. Canonical Correspondence Analysis of the diatom and environmental data revealed three groups of sites, (1) high water-colour and low pH, (2) low conductivity and low water-colour, and (3) high conductivity and higher pH. Diatom species frequency abundances were most strongly influenced by water conductivity and pH. Diatom assemblages were composed of both cosmopolitan and regionally endemic Subantarctic speci...