Pea Crabs

Has anyone else been feeling a little crabby lately?

Over the last two weeks, the FOS Research Team harvested and processed 60 adult Eastern oysters (Crassostrea virginica) to determine their physiological condition. This data will be used to determine the overall health of adult oysters on restored intertidal oyster reefs in the Saint Lucie Estuary and southern Indian River lagoon in Florida. While gathering this information, they found a few unexpected residents living inside several of the harvested oysters. These little creatures, known as Pea Crabs (Pinnotheres ostreum) or Oyster Crabs (Zaops ostreus), are small soft-bodied crustaceans that enter adult oysters early in their development and continue to live and grow inside the oysters for the duration of their life. Pea crabs use the oyster as a food source and are able to consume excess phytoplankton and algae filtered out of the water column by the host oyster. This is called kleptoparasitism, where one animal takes food that was caught or collected by another animal to survive. This process does not harm the oyster unless food availability or tissue reserves become limited. Pea crabs and oyster crabs have long been considered a delicacy, and may cost up to three times as much as oyster meat. An article published by The New York Times in 1907, describes oyster crabs as one of George Washington’s favorite foods, and even includes a brief recipe:

                “Arrange a small mound of oyster crabs on a crisp leaf of lettuce and cover lightly with a mayonnaise that has been tinted a faint pink by the use of beet juice. Garnish with tiny bits of lemon. The crabs are also delicious if fried in much the same manner as one would fry whitebait. To do this dip the crabs in flour, afterward in cold milk, and finally, in powdered cracker crumbs. Put them in a colander and shake them gently... then drop them into very hot fat, but do not let them stay over three minutes. Garnish with fried parsley before serving.”

— The New York Times, "A Rare Delicacy, Little Known"

While Pea crabs are exciting and potentially delicious critters, our team has some budding research questions related to finding these peculiar hermits. Current research suggests that Pea crabs may be found within healthy oyster reef zones. However, other research proposes that the harmful effects of these infestations, like gill damage as a result of the Pea crab roaming within an oyster, may actually decrease their fitness and ability to perform necessary biological functions. Florida Oceanographic scientists will continue to quantify any Pea crabs found throughout the spat settlement study, and assess any trends as we attempt to answer our own questions about how these animals work within oyster reef ecosystem dynamics. Maybe… we all have a little more to be crabby about than we originally thought?

Written by Samantha Smith, a Research Associate at Florida Oceanographic Society. She can be reached at ssmith@floridaocean.org