An updated overview of invasive Caulerpa taxa in Sicily and circum- Sicilian Islands, strategic zones within the NW Mediterranean Sea

The spread dynamics of invasive Caulerpa taxa (i.e. Caulerpa cylindracea, C. taxifolia var. taxi- folia and C. taxifolia var. distichophylla) in Sicily and circum-Sicilian Islands, based on relevant publications, grey literature, unpublished data and in situ observations during the last 23 years, is presented here and discussed. Their known distribution is mapped. New records are also reported. Transport-stowaway is considered the most plausible vector of introduction of invasive Caulerpa in the area. The three invasive taxa showed different spread dynamics. Caulerpa cylindracea and C. taxifolia var. distichophylla, behaved as highly successful and fast-spreading taxa, i.e. as true invasive taxa. On the contrary, C. taxifolia var. taxifolia did not behave like the others, remaining limited to two small areas distant from each other. Due to their geographical position, Sicily and circum-Sicilian Islands are particularly vulnerable to biological invasions and therefore they could play an important role as receiver, transit and donor zone for alien species within the Mediterranean Sea. The creation of permanent observatories and alarm systems in this area might be an effective tool in the management of present and future introductions of alien species in the Mediterranean Sea.