The effects of parasitism by the barnacle Loxothylacus panopaei (Gissler) (Cirripedia: Rhizocephala) on growth and survival of the host crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae)

The crab Rhithropanopeus harrisii (Gould) (Brachyura; Xanthidae) was infected in the laboratory with the parasitic barnacle Loxothylacus panopaei (Gissler) (Cirripedia; Rhizocephala). Crabs and barnacles were collected in the Rhode River in the Chesapeake Bay, MD. Forty-three out of 153 R. harrisii, including stages from megalopa «1 mm of carapace width) to crab 8 stage (:±:8 mm of carapace width), developed a mature parasite (externa) after exposure to rhizocephalan cypris larvae. The duration of the internal phase of the parasite (from infection to the emergence of the externa) averaged 33 days and was independent of host size. Recently emerged externae (virgin externae) exposed to male cypris larvae, matured after fertilization in an average of 15 days. Host molting frequency and molt increments did not differ significantly between parasitized and control crabs. Survival to the crab 9 stage (:±:9.5 mm of carapace width) was 6% for hosts parasitized during the megalopal stage «1 mm of carapace width), while it was 50% for the controls. The results of this study are discussed relative to the prevalences of L. panopaei found in the Chesapeake Bay.