Seaweed Flora and Vegetation of the Aegean Sea

An updated overview of the marine seaweed (macroalgae) flora and vegetation of the Aegean Sea coasts is provided. The total number of species and infraspecific taxa currently reported from the Aegean Sea reaches 600 taxa in total by 2020, of which 183 taxa are pending confirmation of their presence. Additional taxa are treated as excludenda or inquirenda (42 and 34 taxa, respectively), which underlies the taxonomic difficulties, particularly concerning certain genera (e.g. Polysiphonia, Cladophora, Lithophyllum). Moreover, new alien introductions have further increased the known diversity of seaweeds in the Aegean Sea. When it comes to the marine vegetation of the Aegean Sea, the Cystoseiretum association is described as one of the most typical communities of the upper infralittoral zone in undisturbed-pristine areas of the Aegean Sea. Its community corresponds to a “virtual list” of seaweed species that reflects the reference conditions, as they are defined in the Water Framework Directive. However, Cystoseira communities of the Aegean Sea, and in general the marine seaweed vegetation, face today severe degradation under varying pressing factors, such as the overgrazing by the sea-urchin over-populations and the alien herbivorous fish (Siganus spp.).