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.
