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 i nfected in the laboratory with the parasitic barnacle Loxothylacus pan opaei (Gissler) (Cirripedia: Rhizocephala). Crabs and barnacles were c ollected 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 matur e parasite (external after exposure to rhizocephalan cypris larvae. Th e duration of the internal phase of the parasite (from infection to th e emergence of the external averaged 33 days and was independent of ho st size. Recently emerged externae (virgin externae) exposed to male c ypris larvae, matured after fertilization in an average of 15 days. Ho st 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 me galopal stage (<1 mm of carapace width), while it was 50% for the cont rols. The results of this study are discussed relative to the prevalen ces of L. panopaei found in the Chesapeake Bay.