2014 Volunteer for a Survey of Introduced Parasites on Native Mud Crabs in Chesapeake Bay 

June 20-22 and August 22-24
Registration Required!

Project Description

The reproductive bodies of the Loxothylacus panopaei parasite protruding from the abdomen of a White-fingered Mud Crab.

An introduced parasite is affecting native mud crabs in Chesapeake Bay. The parasite Loxothylacus panopaei (Loxo for short) is a type of barnacle that is exceptionally modified, with a highly evolved life cycle tailored for its life as a crab parasite. Loxo larvae are free-swimming. Female larva infect recently molted crabs by burying into the carapace. Once inside she undergoes a series of physiological and morphological changes and assumes control over the host crab, controlling major functions such as molting and reproduction. After a time Loxo grows into a reproducing adult and forms small sacs (reproductive bodies) that emerge through the abdomen of the crab, usually after the crab molts. After fertilization by a free-swimming male Loxo, the sacs are filled with of thousands of larvae that are released into the water to seek out a new crab host. This process eliminates the crab’s ability to reproduce and results in the crab caring for the developing larvae of the parasite. Both male and female crabs are parasitized and both are tricked into caring for the larval parasites.

Loxo are native to the Gulf of Mexico, the Caribbean, and parts of Florida and parasitize several species of mud crabs throughout this range. The first discovery of the parasite in Chesapeake Bay was in 1964 on the native White-fingered Mud Crab (Rhithropanopeus harrisii) in the York River. The parasite is now common in much of the Bay, but the population and abundance varies greatly between years. Mud crabs are easily transported with oysters, and Loxo was likely transported to the Chesapeake with mud crabs caught up in shipments of oysters from the Gulf of Mexico.

SERC volunteer Donald Mitchel Brumsted dumps a crab collector on the sorting screen. Photo by Monaca Noble

Intern Kristin Maglies and SERC biologist Jessica Morris sorting through the oyster shell picking out all of the mud crabs. Photo by Monaca Noble

Researchers at the Smithsonian Environmental Research Center (SERC) having been studying the prevalence of Loxo in populations of the White-fingered Mud Crab, R. harrisii, since the 1990s in hopes of understanding how this introduced parasite affects the mud crab population. The White-fingered Mud Crab is native to and abundant in Chesapeake Bay. Starting in 2003, Dr Gregory Ruiz and others have collected mud crabs every summer from ten sites in Maryland including sites near Queenstown, Centerville, Oxford, Aqualand (near the Governor Harry W. Nice Memorial Bridge), Combs Creek, Broomes Island, Harrington Harbor, Deale, Corn Island and SERC.

At each site volunteers will hand-collect crabs from habitat collectors, or crab condos, which are small plastic crates filled with dead oyster shells that sit on the surface of the sediment. These crates stay in the water for two months, during which time mud crabs take up residence between the oyster shells. After two months, each crate is pulled up and the crabs are hand-collected from the oyster shell habitat. Back in the laboratory SERC staff will measure, sex, and examine the crabs for outward signs of the Loxo parasite.

Volunteer Information

This year we are inviting volunteers to join in the collection of the mud crabs. Collection will take place June 20-22 and August 22-24. We can accommodate a maximum of 12 volunteers per day, two teams of six. But we have a waiting list because we expect some last minute cancelations. We prefer volunteers 15 years old or older, younger volunteers are welcome with parental supervision, but please note this project is not appropriate for young children. 

Volunteers will be separated into two teams. Each team will collect crabs at one or two sites per day. A total of ten sites will be surveyed, two on Friday and four on Saturdays and Sundays (two per team on each weekend day). In general the 12 volunteers will be divided into teams based on their availability (whole day vs half day), and whether or not they are meeting us at a particular site or leaving from SERC in the vans.

What to bring: Please bring a lunch if volunteering all day, water will be provided. Ware clothing that can get damp and muddy. We will not to in the water, but you can still get your feet wet. Be prepared to be outside. Bring rain gear, we will not work in heavy rain, but will work in light drizzle. At many sites will be working out in the sun with little shade, so come prepared.

Transportation is provided for volunteers who are available the whole day, we can not provide transportation for half day volunteers. Vans will be leaving SERC at 8am on Saturday and Sunday and returning by ~4pm (plus or minus an hour). If you'd like to visit a particular site, maybe one near your home, please let us know and we can arrange to meet you there.


Sign up through the Doodle Poll and contact Monaca Noble (noblem@si.edu or 443-482-2467) or Darrick Sparks (443-482-2455, sparksd@si.edu) for more information and to provide your contact information. We will need your email and phone to coordinate meeting places and to notify you in case of cancelation.

Sampling Schedule and Site Locations



Team 1 SERC dock Aqualand       Combs Creek Queenstown Deale
Team 2 Corn Island (SERC) Centerville Oxford Brooms Island Harrington Harbor

Site locations: The locations of our 10 sampling sites are marked on the map. For more detailed information you can use this Google Earth file. This file contains the address and locations of all of the sites, but we're happy to email you addresses if you need them.



Watch the video below for an inside look at the Loxo parasite:

Summary taken from the September 2012 feature story.