The rhizocephalan barnacle Loxothylacus panopaei (Gissler, 1884) is a parasitic castrator that infects xanthid crabs and is invasive on the US Atlantic coast. It was introduced with infected crabs to Chesapeake Bay in the mid-1960s, and has since expanded north to Long Island Sound, New York, and south to Cape Canaveral, Florida. Results of an 8-mo field study (January-August 2012) indicate mean monthly L. panopaei prevalence of 18.2% + 6.2 (mean ± 95% CI; n = 66/384; monthly range 9.4%-30.3%) in Eurypanopeus depressus (Smith, 1869) in Clambank Creek, North Inlet, South Carolina. Prey consumption was compared between parasitized (externa-bearing) and unparasitized (externa-lacking) E. depressus 8-13 mm carapace width. Parasitized crabs (n = 43) consumed significantly fewer (median = 2) mussels (5-9 mm shell height) than unparasitized crabs (n = 29, median = 4) over 72 hrs, suggesting the ecological role of E. depressus may be modified. The parasite was only found in E. depressus 5.8-14.0 mm carapace width. Unparasitized E. depressus ranged from 2.3 to 17.0 mm carapace width. [ABSTRACT FROM AUTHOR]