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, the lagoons and ponds of the Po Delta and in Pialassa della Baiona in Emilia-Romagna. Uronema marinum was identified for the first time in the summer of 2012, although it has been present since 2008, at least. 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.

Morphology and reproductive features led us to report the occurrence of the alien species Uronema marinum Womerley also in the Mediterranean Sea. This species was identified for the first time in the Lagoon of Venice in summer 2012, although it was present since 2008 at least both in this lagoon and in the Po Delta lagoons and ponds . The species is prevalently associated with thalli of the alien species Agardhiella subulata (C.Agardh) Kraft et Wynne, Solieria filiformis (Kützing) P.W.Gabrielson and the invasive species Gracilaria vermiculophylla (Ohmi) Papenfuss which recently have colonized these transitional environments. The most probable introduction vector was the importation of the Manila clam Tapes philippinarum. At present, U. marinum is spread in the whole lagoons but is particularly abundant in the confined areas where Gracilariaceae and Solieriaceae prevail on Ulvaceae due to the high water turbidity.