Ulva australis Areschoug

3.1 Ulva australis Areschoug

From the analysis of the data obtained from the Lagoon of Venice, we report U. australis Areschoug ( Figure 5 View Figure 5 ) as established in the area between Celestia and Certosa Island, with a good MaQI index. However, the latest samplings also report it in more inland areas of the lagoon, including Porto S. Leonardo and ST14, and with a poor MaQI index.

According to Sfriso et al. (2023), U. australis is now the most widespread NIS in the Lagoon of Venice. It is possible that the species growth is being aided by the decrease in the lagoon ’ s trophic conditions.

This Indo-Pacific species was introduced in the Mediterranean Sea by mollusc farming and recorded, as U. pertusa Kjellman , from the Thau Lagoon ( France) ( Cormaci et al. 2004), the Gulf of Naples ( Flagella et al. 2010) and the Lagoon of Venice ( Manghisi et al. 2011). ITS1 and rbc L data of U. pertusa from Spain suggested their synonymy with U. australis ( Couceiro et al. 2011) . Wolf et al. (2012) confirmed the presence of U. australis in the Lagoon of Venice by analyses based on rbc L and tuf A markers.

Womersley (1984) reported U. laetevirens among synonyms of U. australis , pointing out that the sizes of cells of the lectotype of U. laetevirens were superimposable to those of U. australis . Subsequently, Phillips (1988) considered U. australis to be a synonym of U. rigida .

Furthermore, molecular investigations performed by Kraft et al. (2010) have demonstrated that U. rigida was distinct from U. australis . The recent phylogenetic analysis of rbc L gene sequences by Hughey et al. (2021), supports the taxonomic synonymy between U. laetevirens and U. australis assumed by Womersley (1984).

In the Lagoon of Venice, Sfriso (2010a), probably following Phillips (1988), listed U. australis among synonyms of U. rigida . Santarelli (1931) listed Ulva lactuca f. laciniata (Wulfen) J. Agardh from Trani (Adriatic Sea), indicating the species is synonymous with U. australis Kützing ; as reported by the author, this species was collected in Adriatic Sea also by Van Den Bosch, Kützing and Hauck.

Whereas Schiffner ( Schiffner and Vatova 1938) labelled samples of U. lactuca var. laciniata (Wulfen) J. Agardh , including also the “ f. australis ” in the “ Vatova and Schiffner ” collection, hosted at the Natural History Museum of Venice. Observing these herbarium samples in the “ Vatova and Schiffner ” collection, we do not exclude the possibility that U. australis was already present in the Lagoon of Venice in the early 1990s.