Grateloupia minima (Halymeniaceae, Rhodophyta): new insights on its distribution along the Italian coasts.

Grateloupia minima P. and H. Crouan is a red algal species established in 1867 but placed in synonymy under G. filicina for several years. It was reinstated as a separate species only in 2005 thanks to a molecular based study and its distribution was limited to the northeast Atlantic Ocean (De Clerck et al. 2005). For the Mediterranean this species was reported for the first time in the Etang de Thau (France), where it has been introduced accidentally, probably via oyster cultivation (Verlaque et al. 2015). Similarly, it was found for the first time, also, along the Italian coasts, in the Mar Piccolo of Taranto (southern Italy, Mediterranean Sea), a site of the European LTER network, characterized by an intensive mussel farming activity together with an intense import-export business of bivalve mollusks (Cecere et al. 2011). In transitional water systems the introduction of NIS seaweeds is often overlooked due to their possible morphological similarity with native species. In this case, molecular analyses through the DNA barcoding method have proved to be fundamental in discriminating cryptic introduced species. During this study we analyzed several specimens doubtfully identified as Grateloupia cf. filicina (J.V. Lamouroux) C. Agardh, using the 5P portion of the rbcL plastid marker (rbcL-5P). Molecular analyses were therefore carried out on specimens collected in other two Italian TWS: the Venice Lagoon (Adriatic Sea) and the Caprolace coastal lake (Tyrrhenian Sea). The obtained sequences were compared with those obtained in our previous study on the distribution of G. minima in the Mar Piccolo (Ionian Sea) (Petrocelli et al. 2023). This molecular survey identified all the samples as G. minima P. and H. Crouan, allowing us to include in the distributional range of this species both the Adriatic and the Tyrrhenian coasts.