The European crayfish, Astacus astacus, is a freshwater crustacean that has long been a part of European aquatic environments. This fascinating species holds historical significance, having been a traditional food source for centuries across the continent. Once widespread and abundant, its current ecological status is a cause for concern. The European crayfish now faces significant challenges that threaten its continued existence in its native habitats.
Defining Features and Natural Environment
The European crayfish exhibits a dark brown or black coloration on its dorsal side, transitioning to an olive-brown on its underside. It rarely exceeds 150 mm in total length, though some individuals can reach 170 mm and weigh 270 grams. Its carapace is smooth, though it may feature small granular tubercles along its sides. The rostrum, a projection between its eyes, is flat with two spines near its base. Its broad claws are rough on the dorsal side and reddish-brown on the ventral side.
This species thrives in freshwater conditions, preferring clean, oxygen-rich rivers, streams, and lakes. European crayfish are sensitive to pollution and require a neutral pH range, between 6.5 and 8.5. They are primarily nocturnal, spending their days concealed in burrows or among structures like rocks and vegetation. While they can be found in water depths up to 30 meters, they often inhabit rocky or weedy shorelines in shallower areas, less than 2 meters deep.
Reproduction and Sustenance
European crayfish reach sexual maturity after three to four years and several molting cycles. Mating occurs in October and November, with males developing pronounced hooks on their second walking legs to grasp females. After fertilization, the female carries the eggs attached to her pleopods under her tail until they hatch the following May. The young remain attached to the mother for several days, sometimes up to two weeks, before dispersing.
As omnivores, European crayfish consume a varied diet, acting as both predators and scavengers. They feed on aquatic plants, including detritus, and small invertebrates such as worms, aquatic insects, and mollusks. Their diet also includes carrion, fish eggs, tadpoles, and other crayfish.
Endangered Status and Threats
The European crayfish is listed as a vulnerable species globally, and endangered in some regions. This decline is due to several threats. A primary threat is the crayfish plague, caused by the oomycete pathogen Aphanomyces astaci. This pathogen, introduced to Europe with North American crayfish species, is lethal to European crayfish, leading to widespread population decline since the mid-19th century.
Habitat degradation also contributes to the species’ decline, including water pollution and physical alterations to waterways. Competition and displacement by invasive non-native crayfish species, such as the signal crayfish (Pacifastacus leniusculus) and red swamp crayfish (Procambarus clarkii), also pose a threat. These invasive species outcompete native crayfish for resources and act as carriers of the crayfish plague, accelerating the native species’ decline. Conservation efforts, including reintroduction programs and habitat restoration initiatives, protect remaining populations and prevent further spread of invasive species.
Identifying Native vs. Invasive Crayfish
Distinguishing the native European crayfish from invasive species, particularly the signal crayfish, is important for conservation. The European crayfish, also known as the noble crayfish, has a dark brown to black coloration on its back and olive-brown on its underside. Its claws are broad and rough on the upper side, often the same color as its body, with reddish to brown undersides. The carapace is smooth with small granular tubercles on the sides.
In contrast, the signal crayfish (Pacifastacus leniusculus) is identified by a white or turquoise blotch on its claw hinge. Its claws have bright red undersides, and the overall body color ranges from brown to greenish-brown. Signal crayfish are larger, reaching up to 16-18 cm, compared to the European crayfish, which is usually under 15 cm. Recognizing these physical differences is important for monitoring and managing crayfish populations, helping to prevent the spread of invasive species and the diseases they carry.