Structuring effect of environmental variables on protistan diversity patterns in two anoxic marine basins

The tenet that 'everything is everywhere, but the environment selects' has influenced microbiology for several decades, and is still debated controversially. However, the proof or disproof of the hypothesis still remains difficult. Scant data from prokaryotic studies suggest that at least over large distances historical separation may overwhelm environmental effects, challenging the above mentioned hypothesis. Though, at smaller spatial scales, environmental effects seem to dominate diversity patterns, while distance effects are of secondary importance. We tried to contribute to the ongoing discussion by investigating patterns of protistan diversity from two geographically separated marine anoxic basins (Cariaco Basin, Venezuela, Framvaren Fjord, Norway). To take distance and environmental effects into account, each basin was sampled at two different locations along an environmental gradient. Biodiversity patterns were analyzed by applying the 454 sequencing technique. Resulting data sets were used to examine overall diversity of samples under study and to compare recorded community patterns based on taxonomic composition and similarity indices. By combining our results with contextual data from both sampling sites we tested for distance effects in relation to contemporary environmental effects.