Detection of alien macroalgal species in the Mediterranen sea using the DNA barcoding tool

The introduction of non-indigenous species (NIS) across the major European seas is a dynamic non-stop process. A wide range of vectors, such as aquaculture, shipping (fouling, ballast water), lessepsian migration, aquarium trade, fishing nets, are currently introducing a plethora of alien marine species into indigenous assemblages. At present, the knowledge of both diversity and distribution of most genera of macroalgae in the Mediterranean Sea is almost entirely based on morphological studies and published papers dealing with molecular data are limited. Due to their cryptic diversity, many algal NIS may go unnoticed and previous unrecorded taxa in a certain site could be possibly overlooked due to the variability and unreliability of accepted morphological diagnostic characters. Our data cover mainly the area of the Strait of Messina (including Cape Peloro lagoon), Venice lagoon, Thau lagoon, Tunisia, and occasionally other sites in the Mediterranean Sea. Over the ten years, the DNA barcoding tool revealed the presence of various NIS: the Rhodophyta Agardhiella subulata (1), Hypnea cervicornis and H. cornuta (2, 3), Pachymeniopsis gargiuli (4), and Spermothamnium cimosum (3, 5), and the Chlorophyta Ulva australis (= U. pertusa), U. laetevirens, U. ohnoi, and the doubtful unit U. “fasciata” (6, 7, 8). Accurate biodiversity assessment of marine macrophytes is essential for monitoring of biological introductions, it is critical for environmental management and to adequately evaluate temporal changes. DNA barcoding proved to be useful for such floristic knowledge (3, 8). However, the actual picture of the presence of macroalgal NIS in the Mediterranean as a whole is far to be clarified and our work aims to be a step towards its clarification. Yet, the current taxonomic, biogeographical and ecological data gaps can be filled only by cooperative work and standardized methodologies. DNA barcoding demonstrated as a fast and effective tool for: a) the accurate identification of alien species and the evaluation of their vectors (1); and b) the genetic labelling of challenging taxa, especially in those areas subjected to anthropogenic disturbances and quick changes of biodiversity. Data collected in such perspective are also valuable to increase the BOLD system catalogue (9), amplifying the biodiversity knowledge linked to geographical information, which becomes freely available for the scientific community. DNA barcodes are permanent labels assigned to specimens regardless any subsequent taxonomic or nomenclature variation.