Phycogeography of freshwater phytoplankton: traditional knowledge and new molecular tools

Everything is everywhere, but environments selects. Is this true? The cosmopolitan nature of algae, including phytoplankton, has been highlighted in many textbooks and burnt into the minds of biologists during their studies. However, the accumulating knowledge on the occurrence of individual phytoplankton species in habitats where they have not been seen before, reports on invasive phytoplankton species, and the increasing number of papers with phylogenetic trees and tracing secondary metabolites, especially cyanotoxins, contradict. Phytoplankton species, with rare exceptions, are neither cosmopolitan, nor ubiquists. In this review paper, we provide an overview of the basic patterns and the processes relevant for biogeography of freshwater phytoplankton. The following topics are considered: dispersal agents and distances; survival strategies of species; geographic distribution of different types; patterns of invasions; tools of molecular genetics; and metabolomics to explore dispersal patterns, island biogeography, and associated species-area relationships for algae.