Behavior of Estuarine Crab Hosts as Affected by Parasite Infection

Parasites are an understudied portion of ecosystems, considering the impacts they have on their host species. Marine invertebrates such as crabs serve as both primary and intermediate hosts for several different parasite species. In the Chesapeake Bay region, the white-fingered mud crab (Rhithropanopeus harrissi) has been shown to host entoniscid isopods (Cancrion and Cryptocancrion spp.), a rhizocephalan barnacle (Loxothylacus panopaei). Given previous studies that parasites can change host population densities, alter predator-prey dynamics, and impact food web function, we sought to determine how parasite infection affects crab host behavior in the presence of a predator. These parasites are not trophically transmitted; if the host dies, they do too. Therefore, we hypothesize that infected crabs will spend more time hiding and resting compared to uninfected crabs. To test predator response, crabs were placed into an aquaria with open space and shelter habitat available. Their habitat use and behavior were videoed and calculated before and after the addition of a blue crab predator scent cue. Preliminary results show that uninfected crabs spend less of their time moving and more hiding and resting, as compared to their infected counterparts. This project will continue in the fall of 2026, expanding the sample size of crab hosts across all infection statuses.

Hello my name is Kirsten and I am an undergraduate researcher in Dr Fowler’s aquatic biology lab here at the Potomac Science Center, and my project for Oscar for this semester is looking at parasite infections in crab hosts and how it affects the behavior at- specifically the white finger mud crab or Rhithropanopeus harrisiiand two parasites that are found in it. One is Loxothylacus panopaei which is a parasitic barnacle that is actually invasive to the Chesapeake bay and it is a barnacle that creates an externa on the outside of the crab’s reproductive organs and it has a lot of morphological changing properties. It feminizes the male crabs and it completely castrates all crabs. I’m also looking at a species of Cryptocancrion which is an entoniscid isopod. The thing about both these parasite species is they are not tropically transmitted. That means thatif the host dies the parasite dies. So this led me to hypothesize that an infected crab is going to spend less time doing bold activities. That means it’s going to have an increase in hiding and resting and a significant decrease in moving around- especially in the presence of a predator. So what does it look like for us to test this? We have an aquaria setup where we are simulating conditions of both presence of predator and absence of predator. We use scent cues which are frozen ice cubes- the predator cue ice cube has frozen water that a blue crab was marinating in and the control ice cube has plain water with no predator scent. The aquaria has water that the crabs are acclimated too, a base layer of substrate along the bottom, a shelter that is comprised of PVC and tiles, as well as a red light because red is the go-to for crab behavioral studies, and a hammock that is saran wrap where the ice cube can rest.
For each crab each experiment starts with an acclamation period where they’re allowed to be in the tank for 20 minutes before they are videoed. Then we start the video and we record a control period – so this has no scent ice cube- It is just the crab in the tank. And then we add either the control ice cube or the predator ice cube with the scent cube and we record again. Then afterwards I analyze this with for an ethogram. So I have a whole suite of behavior options and a suite of location options. At 30 second intervals I record what the crab is doing and where it is, So for our preliminary results we simplified these behaviors into three categories: resting, moving, and hiding. This graph is showing theproportion of times that crabs are spending in these different activity levels per their infection status. And as you can see the uninfected crabs are actually showing less time moving and more time resting and hiding. This graph is again showing proportion of time I these different activity bins but it is showing these in the different cue presences. So we have the control, the predator, and the no cue. And we would expect there not to be a big difference between the no cue and the control cue because there’s no scent on that control cue. But we are noticing here on this percent change graph that there is a
difference which is indicating that maybe it is the ice cube itself that is impacting the crab’s behavior not so much the scent cube I am continuing this project in the fall as an independent research project where I will be increasing the amount of replicates we have across all infection statuses. So hopefully this will allow us to draw some cool conclusions about how parasite level is affecting crab behavior and itwill culminate in a publishable unit. I want to thank you guys for listening and thank you Oscar for funding this project for the spring of 2025.