Larval Trajectories: Researchers Set Their Sights on the Chinese Mitten Crab

April 16, 2010

The Chinese mitten crab (Eriocheir sinensis) is native to rivers and estuaries on the east coast of Asia, and is considered a delicacy in its Asian homeland. Chinese citizens will pay hundreds of Yuan to taste even a small crab from the Yangcheng lake, as this crustacean is supposed to have a cooling (yin) effect on the body. In other parts of the world, however, what the Chinese mitten crab has been up to is anything but cool. IN the early 1900’s, isolated populations of this species began to appear in northern European countries such as Germany. The Chinese mitten crab has made its way to America through several vectors such as ballast water and unintentional releases, and the area experiencing the most rapid crab invasion is the San Francisco Bay Area.

It’s no secret why these crabs are considered an invasive species when it comes to outlasting their environment. Unlike most freshwater crustaceans, Chinese mitten crabs can survive in marine and even polluted waters, and tolerate uptake of heavy metals, such as Cadmium, for several days. They also have the ability to cross natural barriers such as rapids or dams. Chinese mitten crabs also have a variety of detrimental effects on their environment. E.sinensis is very aggressive, and often outcompetes native crayfish and crab species for resources like space and shelter, as well as food sources.

Mitten crabs often clog pumps, screens, and intakes, and they continue to get caught in shrimping nets, costing the shrimping industry a lot of time and money. Sediment loss and erosion has been shown as an effect from the burrowing of Chinese mitten crab, causing damage to stream banks and levees. Several methods of control have been tried, such as placing traps upstream to catch young crabs during migration, but none have successfully been able to reduce the Chinese mitten crab invasion. The damage that these crabs have caused to the environment is what has led researcher Emilia Rybak to further investigate what can be done.

Modeling their experiment after research done by Cecily C. Natunewicz, Charles E. Epifanio, and Richard W. Garvine, Rybak and her team of researchers aim to see if they can track larval trajectories, or the small migratory pathways of the patches of eggs. This will allow them to see what environmental factors are most responsible for the dispersal of larval patches, and if there is any hope of being able to control the Chinese mitten crabs from their egg stages. Rybak and her team intend to tag separate larval patches in the San Francisco Bay with satellite-tracked drifters attached to buoys at the surface. While doing this, they will be keeping track of physical conditions such as salinity, temperature, and river discharge. This should allow them to simulate general patterns of larval transport and will be helpful in assessing the correlation between the small scale movement patterns and the general trajectories of larval patches.

Rybak and her team all acknowledge the dangers of letting the Chinese mitten crab populations go unchecked in the United States, particularly the San Francisco Bay area. She hopes that her research will shed light on the migratory pathways of Chinese mitten crab larval patches. This will hopefully, in turn, allow for the development of more effective management techniques and the prevention of population growth by targeting the problem in its earliest stages.