Participatory Science ProjectChesapeake Bay Parasite Project
  • Group measuring fish

    Chesapeake Bay Parasite Project

    Volunteers count fish

  • People in a boat

    Chesapeake Bay Parasite Project

    SERC staff collecting crab traps

About the Project

White-fingered mud Crabs (Rhithropanopeus harrissi) are native to the Chesapeake Bay. These scavengers are small, and live in oyster reefs and woody debris in the water. Mud crabs typically live less than 2 years, which means they don’t have a long time to reproduce. The parasitic barnacle that infects these mud crabs is called Loxothylacus panopaei (Loxo, for short). Loxo infects and castrates the crabs, which means they can no longer reproduce. Loxo is an invasive species, which means that they have been transported from their native home and harm the ecology and economy of their new environments. Not all foreign species are invasive, and some get along very well with new neighbors. Loxo, however, is aggressive. Loxo takes control of the crab and changes major functions like molting and reproduction. The infected crabs have been nicknamed "Zombie Crabs" as a result. When the crabs are infected, the parasite produces a sac-like growth on the abdomen of the crabs. These sacs are the reproductive bodies of the parasite. The sacs are filled with thousands of eggs that are fertilized by a male Loxo attached to the inside of the sac. The resulting larvae are then released into the water to seek a new crab host. Both male and female crabs can be parasitized, and both are tricked into caring for the larvae of the parasites.

Mud crabs are an important part of the Chesapeake Bay, they are important predators that play a key role in the food web structure of this ecosystem. They may also be an indicator species, which means that the health of their population is a direct reflection of the health of their habitat, which includes oyster reefs. Scientists want to know how Loxo affects the mud crab population—are mud crab populations steady? Or are they declining because Loxo does not let them reproduce? They will find the answer to this question by studying

  • Size of the crab
  • Sex of the crabs
  • Presence or absence of outward signs of the Loxo parasite.

History of Loxo

Loxo are native to the Gulf of Mexico, the Caribbean, and parts of Florida, Mud crabs are easily transported with oysters, and Loxo was most likely transported to the Chesapeake with mud crabs in shipments of oysters from the Gulf of Mexico. Sometimes people intentionally bring a new species into an area, without realizing the harm it or its parasites can do to the environment. The parasite is now common in the Bay, but the population and abundance varies greatly between years, and scientists are still trying to figure out why these fluctuations happen.

Scientists at SERC have been studying Loxo since the early 1990’s! Starting in 2003, scientists have collected mud crabs every summer.