The Chinese mitten crab ('; ,
"big
sluice
Sluice ( ) is a word for a channel controlled at its head by a movable gate which is called a sluice gate. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway and can be considered ...
crab"), also known as the Shanghai hairy crab (,
p ''Shànghǎi máoxiè''), is a medium-sized burrowing crab that is named for its furry claws, which resemble
mittens
A mitten is a type of glove that covers the hand but does not have separate finger openings or sheaths. Generally, mittens still separate the thumb from the other four fingers. They have different colours and designs. Mittens provide greater th ...
. It is native to rivers, estuaries and other coastal habitats of
East Asia
East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
from
Korea
Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...
in the north to
Fujian
Fujian (; alternately romanized as Fukien or Hokkien) is a province on the southeastern coast of China. Fujian is bordered by Zhejiang to the north, Jiangxi to the west, Guangdong to the south, and the Taiwan Strait to the east. Its capi ...
, China in the south. It has also been introduced to Europe and North America, where it is considered an
invasive species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
.
The species features on the
list of invasive alien species of Union concern
In 2016, following the EU Regulation 1143/2014 on Invasive Alien Species (IAS), the European Commission published a first list of 37 IAS of Union concern. The list was first updated in 2017 and comprised 49 species. Since the second update in 201 ...
. This means that import of the species and trade in the species is forbidden in the whole of the
European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
.
Description and ecology
This species' distinguishing features are the dense patches of dark
seta
In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. Th ...
e on its claws. The crab's body is the size of a human palm. The legs are about twice as long as the carapace.
Mitten crabs spend most of their life in fresh water and return to the sea to breed. During their fourth or fifth year in late summer, the crustaceans migrate downstream and attain sexual maturity in the tidal estuaries. After mating, the females continue seaward, overwintering in deeper waters. They return to
brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
water in the spring to hatch their eggs. After development as
larvae
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
, the juvenile crabs gradually move upstream into fresh water, thus completing the life cycle.
[
It moves from freshwater habitats to saltwater habitats once it has reached reproduction maturity. The types of estuaries suitable for the mitten crab is large brackish waters for the larva to develop in, and large shallow waters for the growth of the juvenile crabs. An increase in ]microplastics
Microplastics are fragments of any type of plastic less than in length, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. They cause pollution by entering natural ecosystems from a v ...
has had a significant impact on the population as it affects their metabolism, growth, and oxidative stress response in the liver.
The Chinese mitten crab originates from Hong Kong to the border of Korea. It can be found inland but prefers coastal areas. In the Yangtze
The Yangtze or Yangzi ( or ; ) is the longest river in Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flows ...
, the largest river in its native range, Chinese mitten crabs have been recorded up to upstream.[Veilleux, É; and de Lafontaine, Y. (2007). ''Biological Synopsis of the Chinese Mitten Crab (Eriocheir sinensis).'' Canadian Manuscript Report of Fisheries and Aquatic Sciences 2812.] It is known to settle in rice fields by the sea and rivers inland. The crab is found in subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
and temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
regions.
Phylogenetically
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
the crab belongs to the Varunidae
The Varunidae are a family of thoracotrematan crabs. The delimitation of this family, part of the taxonomically confusing Grapsoidea, is undergoing revision. For a long time, they were placed at the rank of subfamily in the Grapsidae, but they ap ...
family which is the newest group of brachyuran crustaceans. Spawning crabs average around in length. Since crabs spawn at the end of their life spans and perish at the end of the breeding cycle, the crabs can live up to 7 (in Germany also 8) years old.
The mitten crab diet is omnivorous. Their main prey consists of worms, mussels, snails, dead organic material, and other small crustaceans and fish.
Reproduction
Mitten crabs start off as fresh-water organisms. In late August, sexual instincts awaken and they begin migrating downstream to the sea, away from their feeding grounds. It is during this migration where the crabs reach puberty and develop their sex organs. The crabs begin to breed in the brackish waters in late fall. The males arrive first and stay in the brackish waters all winter; the females arrive after. The eggs are laid within 24 hours of mating, then attached to the abdomen of the female. After the eggs are attached, the female leaves immediately, heading to the mouth of the river. The larvae hatch from the eggs during the summer, after which they float and drift about the brackish waters. Because the journey to breed for crabs is so great, they only breed once during their lifetimes. The breeding age is normally toward the end of their lifespans. The crabs have sizable egg production count since these crabs only breed once. After the crabs successfully reproduce, they have very little energy and begin to waste away.
Different life stages of the mitten crab:
1) Eggs require pure salt water to mature. 2) Larvae hatch from the eggs in brackish waters. 3) The larvae gradually move from brackish water to fresh water. 4) The final stage of the larvae is the megalopa, which is in length. 5) The megalopa then develop into small mitten crabs in the freshwater.
Invasiveness
This certain species of crab has been spread rapidly from Asia (China and Korea) to North America and Europe, raising concerns that it competes with local species, and its burrowing nature damages embankments and clogs drainage systems. The crabs can make significant inland migrations. It was reported in 1995 that residents of Greenwich
Greenwich ( , ,) is a town in south-east London, England, within the ceremonial county of Greater London. It is situated east-southeast of Charing Cross.
Greenwich is notable for its maritime history and for giving its name to the Greenwich ...
saw Chinese mitten crabs coming out of the River Thames
The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, se ...
, and in 2014 one was found in the Clyde Clyde may refer to:
People
* Clyde (given name)
* Clyde (surname)
Places
For townships see also Clyde Township
Australia
* Clyde, New South Wales
* Clyde, Victoria
* Clyde River, New South Wales
Canada
* Clyde, Alberta
* Clyde, Ontario, a tow ...
, in Scotland. The crabs have also been known to take up residence in swimming pool
A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...
s. In some places the crabs have been found hundreds of miles from the sea. There is concern in areas with a substantial native crab fishery, such as the Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
in Maryland
Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
and the Hudson River
The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between N ...
in New York
New York most commonly refers to:
* New York City, the most populous city in the United States, located in the state of New York
* New York (state), a state in the northeastern United States
New York may also refer to:
Film and television
* '' ...
(both locations where the crabs were first spotted in 2005), as the impact of the invasion by this species on the native population is unknown.
It is generally illegal to import, transport, or possess live Chinese mitten crabs in the United States, as accidental release or escape risks spreading these crabs to uninfested waters. In addition, some states may have their own restrictions on possession of mitten crabs.California Code of Regulations
The California Code of Regulations (CCR, Cal. Code Regs.) is the codification of the general and permanent rules and regulations (sometimes called administrative law) announced in the ''California Regulatory Notice Register'' by California state ...
, Title 14, Section 671 California allows fishing for mitten crabs with some restrictions.
The Chinese mitten crab has been introduced into the Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...
several times but has not yet been able to establish a permanent population.
The Smithsonian is tracking the spread of the Chinese mitten crab and seeking help to determine the current distribution status of the mitten crab in the Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
region. People are encouraged to report any mitten crab sightings, along with details (date, specific location, size) and a close-up photograph or specimen if possible. The first confirmed record along the East coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the coastline along which the Eastern United States meets the North Atlantic Ocean. The eastern seaboard contains the coa ...
was in the Chesapeake Bay near Baltimore
Baltimore ( , locally: or ) is the List of municipalities in Maryland, most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic (United States), Mid-Atlantic, and List of United States cities by popula ...
, Maryland, in 2005.
Chinese mitten crabs have also invaded German waters, where they destroy fishing nets, hurt native fish species and damage local dams, causing damage of up to 80 million Euros. These crabs migrated from China to Europe as early as 1900 and were first documented by official German reports in 1912 from Aller River. After an investigation by German scientists in 1933, it was thought that the crabs migrated to Europe through ballast water in commercial ships. The crabs are the only freshwater crab species in Germany, and their tendency to dig holes has caused damage to industrial infrastructure and dams.
The first time the crab was brought to Europe was most likely by commercial vessels. Ships must fill their ballast water tanks and during one of these filling events, it could have been the spawning time for the mitten crab. Since the larvae are free floating and in size, it would have been easy for them to be swept into the ballast water tank. Once the ship reached Europe and emptied its tank, the crab larvae were released. Over time, this repetition would allow for a prominent mitten crab population in Europe. The crab has spread and can be found in Continental Europe, Southern France, United States of America (the San Francisco Bay), and the United Kingdom. A 15-year period in Germany when the crabs were gradually entering Europe is known as the "establishment phase".
Culinary
The crab is an autumn delicacy in Shanghai cuisine
Shanghai cuisine (; Shanghainese: ''zaon⁶ he⁵ tshe¹''; IPA: ɑ̃¹¹ he⁴⁴ tsʰᴇ¹¹, also known as Hu cuisine (; Shanghainese: ''wu⁶ tshe¹''; IPA: u¹¹ tsʰᴇ⁴⁴, is a popular style of Chinese food. In a narrow sense, Sh ...
and eastern China. It is prized for the female crab roe, which ripen in the ninth lunar month and the males in the tenth. The crab meat is believed by traditional Chinese medicine
Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. It has been described as "fraught with pseudoscience", with the majority of its treatments having no logical mechanism of action ...
practitioners to have a "cooling" (yin
Yin may refer to:
*the dark force in the yin and yang from traditional Chinese philosophy and medicine
*Yīn (surname) (), a Chinese surname
*Yǐn (surname) (), a Chinese surname
*Shang dynasty, also known as the Yin dynasty
**Yinxu or Yin, the S ...
) effect on the body.
Chinese spend hundreds of yuan just to taste a small crab from Yangcheng Lake
Yangcheng Lake () is a freshwater lake about northeast of the city of Suzhou in Jiangsu Province, and ranges in depth from . The lake is -long from north to south, with an average width of from east to west. It is the most famous area of origin ...
, which are considered a delicacy. Crabs from Yangcheng Lake are especially prized, since they are perceived to have sweeter meat. Most of the Yangcheng crabs are exported to Shanghai
Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flow ...
and Hong Kong
Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...
, and high-profit foreign markets. Responding to the spread of the crab to the West, businessmen have started seeing it as a new source of crab for the Chinese market. One proposed scheme involves importing unwanted crabs from Europe, where they are seen as a pest, to replenish local pure-bred stock.
Mitten crabs have exhibited a remarkable ability to survive in highly modified aquatic habitats, including polluted waters.[ Like some fish, they can also easily tolerate and uptake heavy metals, such as ]cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
and mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
. Therefore, the farming and post-harvesting of the species needs proper management if it is used as a food. Concerns have been raised that the population and origin of the crab may be affected because of overfishing of the species in the Yangtze
The Yangtze or Yangzi ( or ; ) is the longest river in Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flows ...
.
In 2010, a Chinese businessman introduced vending machines to sell this species of crab in the subways. The crabs are stored at , which induces a sleep-like state.
File:Gekochte Wollhandkrabben.jpg, Hairy crab is an important part of Shanghai cuisine
Shanghai cuisine (; Shanghainese: ''zaon⁶ he⁵ tshe¹''; IPA: ɑ̃¹¹ he⁴⁴ tsʰᴇ¹¹, also known as Hu cuisine (; Shanghainese: ''wu⁶ tshe¹''; IPA: u¹¹ tsʰᴇ⁴⁴, is a popular style of Chinese food. In a narrow sense, Sh ...
File:Roe inside steamed female hairy crab.jpg, Closeup of the roe inside a steamed female crab
Counterfeit Yangcheng Lake crabs
Counterfeit crabs are a problem in the hairy crab industry. Due to the high demand for hairy crabs specifically from Yangcheng Lake, many vendors sell hairy crabs from other lakes and claim they are authentic Yangcheng Lake hairy crabs. Although only 3,000 tons of Yangcheng Lake hairy crabs were harvested in 2012, more than 100,000 tons of supposed "Yangcheng" crabs were sold.
Identifying counterfeit crabs is a hard task, as the Yangcheng Lake hairy crabs look exactly like other hairy crabs. Technology has been implemented to identify fake hairy crabs, such as laser tags, prints, and barcodes, but these are easily forged. Blockchain-based tracing has also been implemented, where caught crabs are entered into a blockchain. However, most of these efforts to catch fake hairy crabs are foiled by "bathing crabs", or crabs that have been imported from elsewhere to be raised in Yangcheng Lake. These crabs usually spend several hours to a couple of weeks in Yangcheng Lake before being sold as real Yangcheng Lake hairy crabs. Efforts to combat bathing crabs are ongoing.
Management efforts
Management efforts have been shown to be very difficult. This is due to its abundance, high reproductive rate, and high physiological tolerance. All the following efforts were attempted but showed little improvement: "catch as many as you can", migration barriers, trapping, raising awareness, electrical screens, and pulses.
There has been a discussion of capturing the breeding crabs at the river mouths. There have been difficulties in carrying out this plan though. Other strategies such as capturing them when they pile up at dams have proven somewhat effective. The problem arises when the crabs climb the walls of the dams and over into the rivers behind the dams.
References
External links
Species Profile – Chinese mitten crab (''Eriocheir sinensis'')
National Invasive Species Information Center, United States National Agricultural Library
The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Located ...
Mitten Crab Watch
- Smithsonian Environmental Research Center
{{DEFAULTSORT:Chinese Mitten Crab
Crustaceans described in 1853
Edible crustaceans
Freshwater crustaceans of Asia
Grapsoidea
Shanghai cuisine