Shanghai hairy crab
The Chinese mitten crab (Eriocheir sinensis; simplified Chinese: 大闸蟹; traditional Chinese: 大閘蟹; pinyin: dàzháxiè; Shanghainese: du6-zaq8-ha5, lit. "big sluice crab"), also known as the Shanghai hairy crab (上海毛蟹, p Shànghǎi máoxiè), is a medium-sized burrowing crab that is named for its furry claws, which resemble mittens. 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. This means that the import of the species and trade in the species is forbidden in the whole of the European Union.
This species' distinguishing features are the dense patches of dark setae on its claws. The crab's body is the size of a human palm. The legs are about twice as long as the 3–10-centimeter-wide (1–4 in) 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 water in the spring to hatch their eggs. After development as larvae, 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 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 largest river in its native range, Chinese mitten crabs have been recorded up to 1,400 km (760 nmi) upstream. It is known to settle in rice fields by the sea and rivers inland. The crab is found in subtropical and temperate regions.
Phylogenetically the crab belongs to the Varunidae family which is the newest group of brachyuran crustaceans. Spawning crabs average around.mw-parser-output.frac{white-space:nowrap}.mw-parser-output.frac.num,.mw-parser-output.frac.den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output.frac.den{vertical-align:sub}.mw-parser-output.sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}5.5 cm (2+1⁄4 in) 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.
Mitten crabs start off as freshwater 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:
