Ulva (Chlorophyta, Ulvales) Biodiversity in the North Adriatic Sea (Mediterranean, Italy): Cryptic Species and New Introductions

Ulva L innaeus ( U lvophyceae, U lvales) is a genus of green algae widespread in different aquatic environments. Members of this genus show a very simple morphology and a certain degree of phenotypic plasticity, heavily influenced by environmental conditions, making difficult the delineation of species by morphological features alone. Most studies dealing with U lva biodiversity in Mediterranean waters have been based only on morphological characters and a modern taxonomic revision of this genus in the Mediterranean is not available. We report here the results of an investigation on the diversity of U lva in the N orth A driatic Sea based on molecular analyses. Collections from three areas, two of which subject to intense shipping traffic, were examined, as well as historical collections of U lva stored in the H erbarium P atavinum of the University of Padova, Italy. Molecular analyses based on partial sequences of the rbc L and tuf A genes revealed the presence of six different species, often with overlapping morphologies: U . californica Wille, U . flexuosa W ulfen, U . rigida C. A gardh , U . compressa L innaeus, U . pertusa K jellman, and one probable new taxon. U . californica is a new record for the Mediterranean and U . pertusa is a new record for the Adriatic. Partial sequences obtained from historical collections show that most of the old specimens are referable to U . rigida . No specimens referable to the two alien species were found among the old herbarium specimens. The results indicate that the number of introduced seaweed species and their impact on Mediterranean communities have been underestimated, due to the difficulties in species identification of morphologically simple taxa as Ulva .