The Chinese mitten crab (Eriocheir sinensis) has become an infamous invasive species, wreaking havoc on ecosystems across Europe and North America. But where did this troublesome crab originally come from? To understand the mitten crab’s invasive potential, we first need to examine its origins in Asia.
Native Territory in Chinese and Korean Coastal Regions
Records indicate the Chinese mitten crab is native to coastal rivers and estuaries draining into the Yellow Sea in eastern China and South Korea, These regions provide ideal nursery habitats for the crab’s complex lifecycle Major hotspots include the Yangtze River estuary and coastal wetlands of the Yellow Sea,
The Yellow Sea’s intricate network of rivers and wetlands allows mass upstream migration of adult crabs seeking spawning grounds. After mating, females release up to 1 million eggs that hatch into larvae carried downstream by currents. The larvae ultimately settle in brackish estuaries before migrating upstream as juveniles.
Ancestral Stronghold of the Yangtze River System
The Yangtze River delta stands out as one of the most significant cradles of mitten crab abundance. As China’s longest river the Yangtze provides ideal conditions for breeding nursery areas for juveniles, and rich feeding grounds enabling vast accumulations of crabs.
Mitten crabs have been recorded traveling over 1,400 km up the Yangtze from the East China Sea. This expansive habitat allowed the formation of large, resilient source populations, with genetic diversity facilitating adaptation to diverse environments.
Clues to Invasiveness Found in Native Behavior
Within its native range, the mitten crab exhibits several key traits that prime the species for invasion success:
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High reproductive output, with females producing up to 1 million eggs.
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Tolerance of varying salinity levels during the crab’s complex life cycle.
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Ability to migrate long distances between fresh and saltwater.
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Generalist diet of plants and small invertebrates.
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Burrowing behavior that provides refuge from predators and environmental stress.
These innate survival strategies served the crab well in its native waters. However, transported outside Asia, the same behaviors fuel damaging population explosions in vulnerable invaded habitats.
Ballast Water Transports Crabs Across Oceans
The Chinese mitten crab spread beyond Asia in the early 1900s through accidental introductions via commercial shipping. The crab’s ability to survive within ballast water allowed larvae to be transported and released into distant ports.
Initial introductions likely occurred in Germany in the 1900s, with crabs documented in the River Weser by 1912. Over subsequent decades, human-assisted dispersal enabled the crab to colonize waterways across Europe, including England, France, and Scandinavia.
More recently in the 1980s, the crab appeared on the west coast of North America, becoming established in San Francisco Bay. Its remarkable transoceanic leap demonstrates this species’ global invasion risk.
What Does the Crab Look Like and Where Does It Live?
The main identifying features of the mitten crab are the dense patches of hairs on the white-tipped claws of larger juveniles and adults, hence the name mitten crab. The claws are equal in size, the shell (carapace) has four spines on either side, and reaches a width of approximately 3 inches (80 mm). The legs of the adult crab are generally more than twice as long as the width of the carapace. A catadromous species, the adults migrate downstream to reproduce in the brackish waters of estuaries. The females carry 250,000 to 1 million eggs until hatching, and both sexes die soon after reproduction. After a 1- to 2-month period as planktonic larvae, the small juvenile crabs settle out in salt or brackish water in late spring, then migrate, often long distances, to freshwater to rear. In China’s Yangtze River, mitten crabs have been reported 800 miles upstream from the Yellow Sea.
Mitten crabs are omnivores, eating both plants and animals. Juveniles eat primarily vegetation. As they mature, the crabs increasingly prey upon animals, especially small invertebrates including worms and clams. In California, adult crabs have become a major nuisance to anglers, taking a variety of baits ranging from ghost shrimp to shad. Predatory fishes, including sturgeon, striped bass and channel catfish, as well as bullfrogs, raccoons, river otters and wading birds may prey upon the crab.
Mitten crabs are adept walkers on land, and if blocked by dams, weirs or other obstructions during their migration, move readily across banks or levees to bypass them. In Germany, large numbers of mitten crabs left the water at night when they encountered an obstruction, and occasionally wandered the streets and entered houses. In California, mitten crabs have been found on roads and airport runways, in parking lots, yards and swimming pools.
A single male Japanese mitten crab (Eriocheir japonica) was caught in the Columbia River, Oregon in 1998. The species is very similar to the Chinese mitten crab currently found in California, and its presence was most likely the result of someone’s attempt to introduce it to the watershed.
The Chinese mitten crab has a long history as an invader. The crab was accidentally introduced to Germany in the early 1900s. In the 1920s and 1930s, the population exploded and the crabs rapidly expanded their distribution to many northern European rivers and estuaries. Most recently, the River Thames in England has experienced a population explosion of the crabs.
In 1992, commercial shrimp trawlers in southern San Francisco Bay collected the first mitten crabs on the West Coast. Since then, the mitten crab has spread rapidly, established in the San Francisco Bay, and spread to river areas upstream of the Delta. The most probable mechanism of introduction to the estuary was deliberate release to establish a fishery (in Asia, the mitten crab is a delicacy and crabs have been imported live illegally to markets in Los Angeles and San Francisco) or accidental release via ballast water.
Mitten crab population control has been attempted but there is little available information on the results. Mitten crab populations decreased in Europe in the late 1940s.
What is the Chinese Mitten Crab?
The Chinese mitten crab (Eriocheir sinensis) is a burrowing crab whose native distribution is the coastal rivers and estuaries of the Yellow Sea in Korea and China. It has recently become established on the west coast of the U.S. in the San Francisco Bay/Delta watershed in California, posing a potential threat to native invertebrates and to the ecological structure of freshwater and brackish estuarine communities, as well as disrupting some fish and shrimping operations. Although not currently present in the Pacific Northwest, scientists predict that, like the European green crab (Carcinus maenas), it is likely to arrive in Oregon and Washington eventually through larval dispersal or intentional release.
Note: It is illegal to import eggs or live specimens of any species of mitten crab (genus Eriocheir) to the United States under the Federal Lacey Act. It is also illegal to import, transport, or possess live Chinese mitten crabs in California, Washington, and Oregon.
Facts: The Chinese Mitten Crab
FAQ
Where did the Chinese mitten crab originate?
The Chinese Mitten Crab (Eriocher sinensis) is native to East Asia and is considered an established invader in Europe and the United States. The first established US population was in California’s San Francisco Bay and Delta in the 1980s.
How did the Chinese mitten crab get to Maryland?
Its presence in Maryland may either be due to releasing crabs purchased as food (only males are sold), or they may be been introduced by ballast water.
Are Chinese mitten crabs good to eat?
Despite being a delicacy in China, they are often seen as a pest in the West due to their remarkable ability to survive. Like all crab, Chinese mitten crab is packed with protein and is an excellent source of minerals, particular zinc, iron, copper and phosphorus.
Is Chinese mitten crab invasive?
It is native to rivers, estuaries and other coastal habitats of East Asia from Korea in the north to Fujian, China in the south. It has also been introduced to Europe and North America, where it is considered an invasive species. The species features on the list of invasive alien species of Union concern.