The low basin of the Arno River (Tuscany, Italy) as alien species hotspot: first data about Rhithropanopeus harrisii (Crustacea, Panopeidae).
Harbours and ports, especially if located in the nearby of brackish-water environments, can provide a significant chance to biological invasions. To date, in the Livorno port, twenty alien species have been recorded, fifteen of which are established. Presence, abundance, size and sex ratio of the mud crab Rhithropanopeus harrisii, a newly introduced invasive species, have been assessed in six sampling stations along the brackish-water canals between Pisa and Livorno towns. Samplings were carried out in summer and fall 2013. R. harrisii appeared fully established in the majority of the sampling stations. Reproduction occurs between May and July and sex ratio varied between reproductive and post-reproductive period, with females more abundant before the reproduction. Individuals of R. harrisii were more abundant in stations close to Livorno port, whereas they were scarce or sporadic in the northernmost stations, close to the main flow of the Arno River. Due to the high invasive potential of R. harrisii, a closer monitoring of brackish-water environments along the north-western Italian coast is needed, in order to assess and prevent further invasions.