Live and Let Live: Invasive Host, Charybdis longicollis (Decapoda: Brachyura: Portunidae), and Invasive Parasite, Heterosaccus dollfusi (Cirripedia: Rhizocephala: Sacculinidae)

The Levantine populations of the invasive swimming crab Charybdis longicollis have been parasitized by the rhizocephalan Heterosaccus dollfusi, itself an alien, since 1992. The parasite affects the host morphology, moulting, behaviour, causes its sterilization, and induces mortality. The high prevalence of H. dollfusi can be ascribed to the dense population of the host, the year-round reproduction of the parasite that promotes recurrent re-infection, and the recruitment dynamics that likely permit the synchronous development of both host and parasite. After 17 years, despite the high prevalence of the parasite and its injurious impact on the host reproduction, the invasive host-parasite pair has reached an apparent modus vivendi, with no evident reduction in the host population and with recurrent seasonal high rates of parasitization and multiple externae.