Freshwater algae belong to numerous evolutionary lineages and the flora of any aquatic system has many species from some or all of these lineages. These algae have a range in morphology from single cells, flagellates, colonies and unbranched or branched filaments. They inhabit flowing and still waters in the regions where they can be attached (periphyton) or free‐floating (phytoplankton). In terms of biogeography, some algae are generalists having a cosmopolitan distribution; others are specialists either restricted to a particular habitat or geographic region and a third category are invaders from either marine or other freshwater habitats. Typically, the physiology of the alga will determine to which category an alga belongs. Freshwater algae may be distributed by wind, terrestrial and aquatic animals, and humans either intentionally or unintentionally. Our understanding of the biogeography of freshwater algae is somewhat limited and further research is needed.
Key Concepts:
Freshwater algae are diverse in their evolutionary relationships, their morphology (shape and size) and habitats they occupy.
Freshwater algae can be ‘generalists’ having a more cosmopolitan distribution, ‘specialists’ being restricted either in geography or habitat or ‘invaders’ from either the marine system or from freshwater typically outside their historic range.
Generalists tend to be able to tolerate a broad range in physical and chemical environments.
Specialists tend to have more specific physiological requirements or are not as readily dispersed.
Invaders from the marine system are able to survive in moderately low salinity environments.
The invasiveness of some freshwater algae has been attributed to nutrient pollution and potential climate change.
Freshwater algae can be dispersed via animals (aquatic and terrestrial), water, wind and human vectors such as ship ballast and fishing waders.
