Differential escape from parasites by two competing introduced crabs

Abstract

Although introduced species often interact with one another in their novel communities, the role of parasites in these interactions remains less clear. We examined parasite richness and prevalence in 2 shorecrab species with different invasion histories and residency times in an introduced region where their distributions overlap broadly. On the northeastern coast of the USA, the Asian shorecrab <I>Hemigrapsus sanguineus </I>was discovered 20 yr ago, while the European green crab <I>Carcinus maenas </I>has been established for over 200 yr. We used literature and field surveys to evaluate parasitism in both crabs in their native and introduced ranges. We found only 1 parasite species infecting <I>H. sanguineus </I>on the US East Coast compared to 6 species in its native range, while <I>C. maenas </I>was host to 3 parasite species on the East Coast compared to 10 in its native range. The prevalence of parasite infection was also lower for both crabs in the introduced range compared to their native ranges; however, the difference was almost twice as much for <I>H. sanguineus </I>as for <I>C. maenas</I>. There are several explanations that could contribute to <I>C. maenas</I> greater parasite diversity than that of <I>H. sanguineus </I>on the US East Coast, including differences in susceptibility, time since introduction, manner of introduction (vector), distance from native range, taxonomic isolation, and the potential for parasite identification bias. Our study underscores not just that non-native species lose parasites upon introduction, but that they may do so differentially, with ramifications for their direct interactions and with potential community-level influences.