Ulva lactuca Linnaeus

3.6 Ulva lactuca Linnaeus

Samples of U. lactuca Linnaeus ( Figure 4 View Figure 4 ) were collected in stations ST1, ST2, and Porto San Leonardo, all three falling within the inner part of the Lagoon of Venice, a poor-quality area according to the MaQI index. In Lake Ganzirri, the species was collected in ST05.

According to Hughey et al. (2019), the holotype of U. lactuca is the species previously called U. fasciata in the subtropical area and U. lobata in the eastern Pacific Ocean. The current distribution of U. lactuca confirmed by DNA sequences is in the eastern ( Australia) and northern ( India) Indian Ocean, central (Hawai ’ i, USA) and temperate southeast ( Chile, Peru), southwest ( Australia), and northwest ( South Korea, Japan) Pacific Ocean, warm temperate eastern (Azores) and western Atlantic Ocean (including the Gulf of Mexico and Atlantic Florida, USA) and the eastern ( Egypt, Israel) and western ( Italy) Mediterranean Sea ( Hughey et al.

2019). The presence of this species in the two sites in Italy, in Capo Peloro Lagoon and the Lagoon of Venice ( Miladi et al. 2018), might be due to recent introductions as both sites have anthropogenic impacts, also according to Hughey et al. (2019). However, their introduction date might be older. The first record of U. lactuca in the Lagoon of Venice dates to 1987 as U. fasciata ( Sfriso 1987) ; in 1938, Schiffner reported as “ U. fasciata Delile […] has also been collected in the Adriatic at Makarska (Dalmatia); is rare and is often confused with U. lactuca” ( Schiffner and Vatova 1938) .

3.7 “ Ulva linza / procera / prolifera ”

Samples of “ U. linza / procera / prolifera ” ( Figure 4 View Figure 4 ) were collected in spring at the ST 10 in 2018 and at Celestia station in 2010 (Table 1), with a poor and good MaQI Index , respectively. The latter specimen had previously been identified by Armeli Minicante (2013) as U. linza (Supplementary Table 2).

ITS sequence data obtained by Brodie et al. (2007) showed Ulva procera (Ahlner) Hayden, Blomster, Maggs, Silva, Stanhope et Waaland as conspecific with typical Ulva linza Linnaeus. Furthermore, Kang et al. (2014) note that several authors regard U. procera as a separate species from U. linza ( Heesch et al. 2009; Kirkendale et al. 2013; Saunders and Kucera 2010).

The lectotype of U. prolifera O. F. Müller is a drawing in Müller ( Müller 1778), the epitype was designated and sequences for the ITS-2 and 5S rDNA spacer regions generated. The ITS-2 sequence of this specimen was not made publicly available but was reported to be identical to a previously published sequence with GenBank accession number AJ012276 View Materials ( Kuba et al. 2022).

To date, there are two major opinions ( Cui et al. 2018) on the classification of U. prolifera based on molecular markers. One point of view is that the true U. prolifera is included in the linza – procera – prolifera (LPP) complex clade (consisting of U. linza Linnaeus , U. procera (Ahlner) Hayden, Blomster, Maggs, Silva, Stanhope et Waaland , and U. prolifera ), and the other is that U. prolifera forms a separate clade that includes specimens from Scotland and Ireland, while the entire LPP complex clade is U. linza .

Using ITS and 5S rRNA gene spacer region as barcode markers on Ulva LPP complex, U. procera was recently reduced into synonymy under U. prolifera by Cui et al. (2018).

Based on this synonymy, Kuba et al. (2022) identified U. procera specimens from San Juan Islands ( USA) on the basis of ITS-2 sequences, that were 1 – 2 base pairs different (0.47 – 0.93 %) from that of the U. prolifera epitype. However, the San Juan Islands specimens molecularly identified as U. prolifera , were not branched tubes, the characteristic morphology of the species, but distromatic blades that became tubular where they were basally narrow near the point of attachment. This latter morphology has been identified as U. linza in the Northeast Pacific ( Kuba et al. 2022). In the light of these observations, the authors suggest that the concept of U. prolifera needs to be expanded to include blade-form thalli.

The LPP-clade has been a troublesome group, and morphology does not appear to be helpful because this clade is known to have wide-ranging morphologies from linza -like to prolifera -like. Additionally, only tuf A sequence data was obtained for our samples since this has shown to be an excellent barcoding marker for green algae, and therefore, we were not able to compare this sequence data with the 5S rRNA and ITS sequence data from the epitype. For these reasons, we choose to call the clade “ U. linza / procera / prolifera ” as the designation for the samples from the Lagoon of Venice identified in this study. Multi-gene or genomic analysis should be considered in the future.