On the occurrence of Uronema marinum Womersley (Chaetophorales, Chlorophyta) in the north-western lagoons of the Adriatic Sea, Mediterranean Sea (Italy)

We study the occurrence of the alien macroalga Uronema marinum in the lagoon of Venice, in the lagoons and ponds of the Po Delta and in Pialassa della Baiona in Emilia-Romagna. It was in summer 2012 that U. marinum was identified for the first time, even though it has been present at least since 2008. This species, originally described from South Australia and Western Australia and probably imported with the Manila clam Tapes philippinarum, is prevalently associated with thalli of another introduced species, Agardhiella subulata, and the invasive Gracilaria vermiculophylla, which also have a Pacific origin and have recently colonized the same lagoon areas. Uronema marinum is currently widespread in the whole lagoon surfaces, but is particularly abundant in stagnant waters, rich in nutrients, where Gracilariaceae and Solieriaceae prevail on Ulvaceae.