Red Swamp Crayfish (Procambarus clarkii, Girard, 1852)
Origin: Northern Mexico and South-eastern United States
Size: 5.5 to 12 cm (adults)
The Red Swamp Crayfish or Louisiana Crayfish is a warm freshwater crayfish; it is dark red with narrow elongated claws and head; the spines are reduced or absent on the side of the shell (carapace). The first walking leg (cheliped) has bright red rows of bumps (tubercles) on its side, margin and palm; the carapace is not separated at the middle and has a wedge-shaped black stripe on the abdomen. The juveniles are uniformly grey.
This species inhabits lentic (still waters) and lotic (moving waters) freshwater habitats, like swamps, ditches, ponds, marshes, lakes, streams, also rice fields, irrigation channels and reservoirs; it avoids places with a strong flow. It exhibits considerable ecological plasticity and can tolerate different levels of salinity, oxygen, temperature and pollution; constructs simple one open burrow where it hides in periods of drought or unsuitable temperatures (hot or cold). It is territorial and aggressive even with its own species.
The life cycle is relatively short, around four and a half months from the egg until adult stage. Breeding takes place usually in autumn (second period sometimes in spring). The eggs are fertilized externally, and females will carry them during development (attached to the swimmerets of the tail); hatchlings will remain attached to females through two moults, after that they become free. During this period females look for protection inside the burrows. The diet is omnivorous consisting of plant material, animals (molluscs, insects and fishes), detritus and sediments.
The Red Swamp Crayfish is cultivated and consumed for food in the Southern United States and it has an important economic impact. The introduction in Europe was related to commercial issues; it was introduced in Spain in 1973 and registered for the first time in Portugal in 1979 and its now spread along 11 hydrographic basins. This species is in the top 10 of invasive species which cause more ecologic and economic damage; it is responsible for species extinction and habitat destruction, it has already been identified as having a negative impact on some aquatic plants, invertebrates, amphibians and other species. Although the negative impacts in some species the Red Swamp Crayfish is important in high trophic levels, it is an important food source for the Eurasian Otter (Lutra lutra), for other 3 species of mammals, 6 species of birds and 3 species of fishes in the Mediterranean Region.
Recent studies showed that the climate change is affecting the diet of the Red Swamp Crayfish, consuming more plant material, this can have more negative impacts in aquatic plants and in rice production.
In Portugal exists only one native species of crayfish, the White-clawed Crayfish (Austropotamobius pallipes), but is extinct or almost extinct and has the status of Endangered (EN) according to the IUCN (International Union for the Conservation of Nature). The major threats are habitat loss, suddenly climate changes and competition with invasive species like the Red Swamp Crayfish.