Effects of an invasive barnacle parasite and salinity stress on the functional response of the native mud crab Rhithropanopeus harrisii

Abstract

Loxothylacus panopaei, an invasive parasitic barnacle, invaded the Chesapeake Bay from the U.S. Gulf Coast in the 1960s. It infects nine species of mud crabs, including the white-fingered mud crab Rhithropanopeus harrisii, an important prey item and predator in estuarine communities.  Previous work shows that L. panopaei forms an internal network of rootlike rhizoids in its host, castrating them, and may alter infected crabs’ eating patterns, which can have negative effects on native wildlife populations. Both parasite and host also have specific salinity tolerance ranges, where lower salinities are stressful. To test how salinity stress affects the feeding behavior of R. harrisii crabs when infected with L. panopaei, 20 infected and 20 uninfected crabs were acclimated to five levels of salinity (2, 4, 6, 10, and 12 ppt) at five levels of prey density (5, 10, 15, 20, and 50 chironomid insect larvae) and assessed feeding after four hours. Prey consumed was then compared between infected and uninfected crabs to observe whether salinity interacted with infection. Preliminary trials show that at the highest prey density, R. harrisii ate more at higher salinities (70% consumed at 10 ppt and 76% at 12 ppt) than at low salinities (44% at 2 ppt). Infected crabs ate fewer prey than uninfected crabs only at low salinities; there was little difference in feeding between uninfected and infected R. harrisii at higher salinities. These results suggest that low salinity stress interacts with infection status to impact R. harrisii feeding habits.