Monday, September 27, 2021

URSP Student Mounia Hammadi Studies the Potential Effects that Endoparasites Have on Feeding Habits of Their Crab Hosts

The survival of a species of mud crab along the East Coast of the U.S., known as the Rhithropanopeus harrisii (Harris mud crab), is being tested by a multitude of factors, including the continued fluctuations in salinity that result from the estuaries it resides in and the ever-changing levels of parasitism in different locations along the coast. The biotic pressure of parasitism is influential on not only the survival of R. harrisii but also the trophic structure of its community. The two most prevalent parasites that cause a significant role in the survival of the Harris mud crab community include the castrating parasitic barnacle, Loxothylacus panopaei, and the lesser-known parasitic entoniscid isopod, Cancrion sp. Parasitic castration means that L. panopaei inhibits the organism’s ability to reproduce. However, since Cancrion sp. is considered a new species, there is minimal evidence suggesting complete parasitic castration of R. harrisii. This summer I have been working in Dr. Amy Fowler’s lab at the GMU Potomac Science Center answering the question, do these endoparasites affect the feeding habits of their crab hosts? We suspect that the intense energy drain of being infected with these endoparasites leads to changes in the feeding behavior of R. harrisii. Luckily, the COVID-19 restrictions have begun to loosen, allowing me access to the laboratories to run a multitude of feeding trials on a total of 25 uninfected crabs, 8 infected with entoniscid (Cancrion sp.), and 11 infected with L. panopaei where feeding behaviors are accessed for 45 minutes.

The collection of these crabs has been done from three main sites: Boathouse Marina in Colonial Beach, VA, Garrett’s Marina in Dunnsville, VA, and near the Choptank River Bridge in Cambridge, MD. This summer, an interesting observation I had was that the mud crabs can be the host to both parasites at the same time, as shown by an individual crab that acquired L. panopaei externa (sac on the abdomen of the crab that holds thousands of parasitic larvae) as well as released Cancrion sp. larvae. How double infections affect R. harrisii’s feeding habits is still yet to be determined. Another interesting observation was that gravid crabs (those with fertilized eggs) and crab hosts infected with Loxothylacus panopaei in the externa phase will both not molt to minimize loss of its eggs or parasitic externae. However, it has been shown that the crabs infected with the entoniscid do continue to frequently molt where its infection does not inhibit its ability to grow. Although trials are still being run and the data has yet to be properly analyzed, what has been obtained so far is extremely interesting and will further be looked upon during the Fall 2021 semester.