First record of the endoparasitic isopod Portunion maenadis (Giard, 1886) (Epicaridea: Entoniscidae) in shore crabs in the Wadden Sea and a review of its distribution in Europe

Abstract

The knowledge on the distribution and abundance of marine parasites is still limited, even for those occurring on relatively well studied host species with high ecological importance. Here we report on the first record of the entoniscid Portunion maenadis (Giard, 1886) in European shore crabs ( Carcinus maenas L., 1758) in the Wadden Sea and provide a quantitative review of the parasite’s distribution in Europe based on published literature and biodiversity database records. Our new record closes a distribution gap of P. maenadis between previous southern observations in Portugal and France and northern occurrences in Denmark and Sweden. The additional literature survey suggests that P. maenadis is not very common and only occurs at scattered localities with prevalence of infestations usually well below 10% in host crab populations. However, the 45% prevalence observed in our study in November 2018 in the southern Wadden Sea indicates that also higher prevalences can occur. As the adult parasites feed on their host’s hemolymph they are likely to have consequences for the host’s energy budgets. In addition, infestations lead to morphological changes in the form of feminisation of male crabs (i.e. broader pleon, slender claws, bulging carapace) which we observed in several individuals. With this new record and literature review, we hope to spark future research into the distribution of this intriguing parasite species as well as on the impacts of infestations on shore crab hosts.

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