Wednesday, December 19, 2012

a sweet victory for bitter crabs

I recently visited family in Illinois and, while flying there, talked with a fellow passenger about bitter crab disease and the prevalence of it in southeast Alaskan Tanner crabs (Chionoecetes bairdi). In one area, the parasitic dinoflagellate affected 95% of the crabs, and that was back in 1987! Lately some southeast Alaskan populations had 100% of their primiparous females infected (Sherry Tamone talked about that at the Alaska Marine Science Symposium in 2011). Bitter crab is a problem in Alaska, but it is also affecting fisheries off Virginia and along the eastern coastal US, as well as in crab hatcheries in China and lobster populations in Scotland! What is causing this, and how is it spreading? What can fishermen do to quell the infection rate? And how can processors assist the fishermen in this effort?

 an infected Tanner crab (top) with milky hemolymph
and a healthy Tanner (bottom) with translucent hemolymph

Lots of questions, I know. Scientists have been feverishly researching Hematodinium sp, the dinoflagellate that is wreaking havoc on commercial crab species. A group of crab scientists at VIMS were able to trace the life history of Hematodinium sp. "[W]e can now really start picking the life cycle apart to learn what the organism does and how it functions," said Jeff Shields.

(Jeff Shields, VIMS)

The researchers noticed a pattern of development time in the dinoflagellate that correlates with cycles of infection in the field and molting of blue crabs (Callinectes sapidus). This knowledge enables them to make suggestions, at least in the realm of aquaculture, on how to avoid the spread of bitter crab by minimizing any effects the parasite could have on crabs during certain periods of both host and parasite life cycles. It seems small, but it's an important victory 15 years in the making in the battle against bitter crab disease!


  1. I just want to know how you tell if a crab is bitter or just being crabby.

    I asked one once, but he sidestepped the issue...


    1. Bwahahaha!

      But to answer your question, at least for Tanner crabs, the ones with bitter crab disease look like they've been boiled: really red, especially at their joints, and their hemolymph is milky white instead of being clear/translucent. Snow crabs also have milky white hemolymph when infected, and their color overall looks yellow/white instead of their normal light tan. Infected crabs will eventually sporulate, which looks like puking, prior to their death. Super gross.