Observations on parasite and epibiont prevalence in the Levantine population of the Erythrean alien portunid Charybdis longicollis Leene.

The swimming crab Charybdis longicollis, found in the Red Sea, the Persian Gulf andMadagascar, was first recorded in the Mediterranean in 1954. Soon after, its populations underwent an exponential growth stage and nowadays it occurs all along the Levant, from Egypt to Rhodes, being common on sandy-mud bottoms at 25-60 m, where it may form as much as 70% of the benthic biomass. In 1992 it was first found to be parasitized by the rhizocephalan Heterosaccus dollfusi, an Erythrean alien as well. The parasite causes sterilization and prevents moult in its host. The prevalence of the parasite has been monitored from September 2005 to October 2007 off Palmahim (Israel). Seasonal variations in infection range from 42.9% to 69.8% of the sample with a relatively high number of multiple externae per host. In 2007 the epibionts were noted as well – the serpulid Hydroides operculatus which were mostly observed on the thoracic sternites, and the barnacle Chelonibia patula. No correlation was found between the presence of encrusting serpulids/balanids and rhizocephalan parasitation or the number of externae per host. Crabs smaller than a certain size bore no epibionts.