Introduced and Native Populations of a Marine Parasitic Castrator: Variation in Prevalence of the Rhizocephalan Loxothylacus Panopaei in Xanthid Crabs
Patterns of prevalence and host specificity of the parasitic castrator, Loxothylacus panopaei, in a region of parasite introduction (Chesapeake Bay, Maryland-Virginia) were compared to those within its native geographic range (Indian River Lagoon, Florida). Prevalence in five species of xanthid crabs was measured at several spatial and temporal scales along the east coast of North America. The parasite infected Panopeus lacustris, P. simpsoni, P. obessus, Eurypanopeus depressus, Dispanopeus sayi (reported as a host for the first time), and Rhithropanopeus harrisii, but did not infect P. herbstii. The overall prevalence of infection in over 10,000 crabs was low (< 1%); but prevalence exhibited significant large scale geographic variation from 0-83% in the parasite's disjunct distribution along 2750 km of coast and 14 degrees of latitude from New Jersey to western Florida. The introduced range of the parasite included most of Chesapeake Bay, outer Delmarva Peninsula, and North Carolina sounds; but the parasite was not found from South Carolina to Cape Canaveral, Florida. The native range extended from the Gulf of Mexico and eastern Florida up through the Indian River Lagoon. Significant temporal variability of infections occurred between 2 yrs along the geographic range of sampling, with the parasite occurring sporadically (0-47%) in introduced regions of North Carolina and (0-83%) in coastal Virginia. The prevalence of parasitism also exhibited significant local variation among sites within the introduced region of Chesapeake Bay (0-91%) and the native region of the Indian River Lagoon, Florida (0-9%). Parasite prevalence within the Indian River Lagoon exhibited long-term (12 yrs) relative temporal stability at about 7.5% in P. lacustris. In contrast, the parasite exhibited epidemic out breaks (0-72%) in a 15-yr record at the Rhode River subestuary of Chesapeake Bay following its slow spread over 200 km in 30 yrs from introduction in the lower bay in 1963. Size of infected hosts was relatively constant for each crab species, resulting in all sizes of R. harrisii and E. depressus being infected but larger P. lacustris not being infected. Despite the parasite's impact on crab reproduction, the host-parasite interaction is apparently stabilized by shifting combinations of four factors: host species composition; recruitment dynamics, especially slow parasite dispersal; patchy host dispersion in oyster reefs; and reservoirs of uninfected hosts resulting from refuges in host size (e.g., large P. lacustris) or host habitat distribution (e.g., low salinity for R. harrisii).
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Document Type: Research Article
Publication date: 1997-09-01
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