Procambarus clarkii, known variously as the red swamp crayfish, Louisiana crawfish or mudbug, is a species of cambarid crayfish native to freshwater bodies of northern Mexico, and southern and southeastern United States, but also introduced elsewhere (both in North America and other continents), where it is often an invasive pest.
Appearance P. clarkii is typically dark red, with long claws and head, small or no spines on the sides of its carapace just below the head, and rows of bright red bumps on the front and side of the first leg.
Range and range expansion The native range of P. clarkii is from northern Mexico and far southeastern New Mexico, through the Gulf States to the Florida Panhandle, as well as inland north through the Mississippi Basin to southern Illinois. It has also been introduced, sometimes deliberately, outside its natural range to countries in Asia, Africa, Europe and elsewhere in the Americas. In northern Europe, the populations are self-maintaining but not expanding, while in southern Europe, P. clarkii is multiplying and actively colonizing new territories at the expense of the native crayfish, Astacus astacus and Austropotamobius spp. In some areas this species occurs in sympatry with another invasive crayfish, Pacifastacus leniusculus. Individuals are reported to be able to cross many miles of relatively dry ground, especially in wet seasons, although the aquarium trade and anglers may have hastened the spread in some areas (anglers using P. clarkii as fishing bait are thought to have introduced it to the state of Washington). Attempts have also been made to use P. clarkii as a biological control organism, to reduce levels of the snails involved in the life cycle of schistosomiasis, leading to the dispersal of P. clarkii in, for instance, Kenya.
Invasiveness In Europe, P. clarkii has been included since 2016 in the list of Invasive Alien Species of Union concern (the Union list). This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union. In Holland the species threatens the survival of rare dragonflies. Native birds enjoy it as a food source. The authorities are running a campaign to exterminate the crays from Dutch waters using traps that make the crays easy prey for the birds.
Ecology
P. clarkii is most commonly found in warm freshwater bodies such as slow-flowing rivers, marshes, reservoirs, irrigation systems and rice paddies. It is considered to be the most ecologically plastic species in the order Decapoda and is able to grow quickly even in only seasonally present water, being able to tolerate dry spells of up to four months. P. clarkii grows quickly, and is capable of reaching weights over 50 g (1.8 oz) and sizes of 5.5–12 cm (2.2–4.7 in) long. It is also able to tolerate slightly saline water, which is unusual for a crayfish. Additionally, P. clarkii are physiologically capable of tolerating relatively low dissolved oxygen concentrations. The average lifetime of P. clarkii is five years, although some individuals are known to have reached ages (in nature) of over six years. The burrowing activities of P. clarkii can damage existing water courses and crops, particularly rice, and its feeding activities can disrupt native ecosystems. It may outcompete the native crayfish species and is a vector for the crayfish plague fungus Aphanomyces astaci, for crayfish virus vibriosis and for a number of parasitic worms on vertebrates. Their burrowing activities may also be a threat to civil infrastructure such as storm ponds and levees. In 2007, troglomorphic specimens of P. clarkii were found in central Portugal in the karst springs of the Rio Anços in the Sicó massif and of the Alviela River in the Estremenho massiff. In 2011, another cave-dwelling population was discovered in caves in the San Giuliano Terme municipality in the Province of Pisa in Italy. Both localities consist of karst landscapes with extensive cave formations. The Portuguese population is entirely depigmented, although pigmented specimens are present in nearby surface streams; the deepest recorded specimen was a male recovered at a depth of 240 metres (790 ft). 53% of Italian specimens displayed a blue-white coloration. The greater presence of pigmented individuals suggests either a more recent entrance, an external source of carotenoids, or movement between surface and underground waters. Collectively, these potations make up the first recorded instances of troglodytic crayfish in Europe. The invasive crayfish have the potential to pose an environmental threat to native stygobitic fauna, due to the crayfish's recorded ability to prey on diverse sources of food and the highly restricted ranges of native cave fauna.
Economic importance
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