Ascidians in the Port of Ghar El Melh (North of Tunisia): A New Record of the Non-native Ascidian Ciona robusta Hoshino and Tokioka 1967

Ascidians (Phylum: Chordata, Class: Ascidiacea), known as sea squirts, represent the most diversified class of the sub-phylum Urochordata (Tunicata), with approximately 3000 described species. They are considered as one of the most important taxon of the non-indigenous species worldwide. However, in Tunisia, except for some ancient records, ascidians studies are relatively rare. This study aims to describe ascidian species collected from the port of Ghar El Melh in order to enlarge the knowledge of this taxon. Specimens were collected manually from rocks and boat ropes. Taxonomic identification was carried out using the classification of Lahille 1886 and the keys of Monniot et al. (Coral Reef Ascidians of New Caledonia, 1991) and other authors (Hoshino and Tokioka in Publ. Seto. Mar. Biol. Lab. 15:275–290, 1967; Brunetti et al. in Zoolog. Syst. Evol. Res. 53:186–193, 2015). In total, eleven species belonging to six families (Polyclinidae, Didemnidae, Cionidae, Ascidiidae, Styelidae and Pyuridae) were found and identified. There are five non-indigenous species, including Ciona robusta. This latter species is reported for the first time in Tunisia in the port of Ghar El Melh Bizerte (North of Tunisia) by the present study in June 2020. Ciona robusta was distinguished from its congeneric Ciona intestinalis by the presence of tubercular prominences in the tunic around the siphons.