Posted tagged ‘invasive species Hudson river’

Invasion of the Mitten Crabs

February 4, 2012


“from the depths of the sea … A TIDAL WAVE OF TERROR!”

Attack of the Crab Monsters, 1957

Chinese playwright and recent Columbia MFA gradate Zhu Yi, also known as Zoe, recently alerted me to an unusual presence in the Hudson River: Chinese Mitten Crabs.

According to Zhu Yi, mitten crabs are a delicacy in China.

Chinese mitten crab, aka Shanghai hairy crab. Photo from John H. Isacs.

But here in the United States, the Department for Environmental Conservation calls them “our newest Hudson River invader.” Zhu Yi plans to write a play using the mitten crab as a metaphor for our fear of invasion through immigration, which I will hope to see sometime soon.

Most exotic plants and animals, transported out of their native habitats, will not survive. But those that do survive may become invasive, which means they out-compete native species, reducing biodiversity, and changing the balance of local ecology. Often, there are no predators in the new environment to keep the population under control, and the species proliferates without the natural limits of its original habitat. Mitten crabs, which are causing serious environmental problems throughout Europe, are now being found in the Hudson River.

Named for their oddly furry claws, Chinese mitten crabs travel 7,000 miles from home to take up residence in North American waterways by stowing away in the ballast water of ships. Ballast water, it turns out, is a major source of the invasive species that are causing serious problems in our rivers, estuaries and lakes.

Ship discharging ballast water. Photo: World Wildlife Federation

Ships take on water for stability when cargo loads are low. When they pull into a port and load up on cargo, they discharge water that may have come from halfway around the world. Ballast water, which may be fresh, brackish or salt, is home to untold numbers of plants and animals – plankton, seaweeds, algae, invertebrates, bacteria – that are swept up into the ship’s hold, and later released in new environments.

Chinese mitten crab, up close and personal. Photo: S. Gollash

Mitten crabs are fascinating creatures. They spend most of their lives in fresh water, where they burrow into river or stream banks, causing soil erosion and habitat loss.  But they must travel each year back to the sea to mate. To do this, they walk. Yes, walk. Mitten crabs are “walking crabs,” able to travel long distances – “up to several hundred miles,” according to the DEC – over land by walking on the tips of their pointy claws. Londoners have described them coming up out of the Thames to walk the streets on their migration.

Still image from Attack of the Crab Monsters.

If you find or catch a Chinese mitten crab, the DEC has a few requests:

  • Do not release it back to the water
  • Keep it and freeze it (preserve in alcohol if you can’t freeze it)
  • Note date and location caught (GPS coordinates preferred but pinpointed on a map is acceptable) and how you caught it
  • If possible, take a close-up photo. You may e-mail photo to SERCMittenCrab@si.edu for identification.

Don’t eat it!  Mitten crabs, like some fish, can accumulate large amounts of heavy metals from their environment – and, after all, who knows where this crab has been?

Just don’t try telling that to the man and woman on the street in China, where a horrific new vending machine sells live packaged (probably farmed) crabs to subway commuters. They are kept cold enough that they are in a state of semi-hibernation, but still alive, sealed into tiny plastic containers.

Can you really wonder if the crabs have their revenge?


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