Does Salinity Influence the Spatiotemporal Distribution of Two Castrating Parasites of an Estuarine Mud Crab Host?

Estuarine organisms can utilize salinity extremes to evade competition, predation, or parasitic infection but with the cost of osmotic stress. In the Chesapeake Bay, the mud crab Rhithropanopeus harrisii (Rh) is parasitized by the invasive rhizocephalan barnacle Loxothylacus panopaei (Lp) the newfound isopod Cryptocancrion brevibrachium (Cb). Both parasites castrate their host, however the degree of Cb’s castration is unknown. Rh lives in salinities between 0.5-25ppt while Lp cannot survive <10ppt. We theorized that Rh could escape castration by moving to salinities <10ppt; however, Cb occurs in these low salinities. To determine if a true environmental refuge against castration exists for Rh, Rh from nine Chesapeake Bay populations were collected and dissected bi-monthly for 18 months to capture host-parasite seasonality and quantify individual and reproductive stress. This research will determine how salinity shapes the spatiotemporal distribution of Rh and its endoparasites and elucidate to what extent these parasites impact Rh reproduction. Survival experiments were also conducted to determine the low salinity tolerance of Cb’s first larval stage, which are expelled from Rh and swim to find an intermediate host – a copepod. We found that a Cb infection leads to reduced gonad and hepatopancreas weight in both sexes of Rh, where infected female’s gonads are completely absent, suggesting complete castration of female crabs. Cb co-occurs with Rh in all salinities as low as ~1 ppt in the Chesapeake Bay, effectively refuting the hypothesis of a low salinity refuge from castration. However, Cb larvae survive poorly in salinities <6 ppt, thus the mystery of their success in low salinities as adults in Rh remains due to aspects of their lifecycle still being unknown (i.e., copepod host species, larval dispersal ecology, length of larval development). This unique host-parasite relationship can reveal how selective tradeoffs in dynamic environments such as estuaries can shape host distribution and ecology.

Author

• Greenberg, Sarah R

• castration
• larval development
• invertebrate ecology
• Chesapeake Bay
• host-parasite relationships
• salinity

Identifier

hdl:1920/15050

OAI identifier oai:identifier

oai:MARS:1920/15050