Among the fauna found in rivers we have al River crab. It is a decapod arthropod whose body is covered by a shell. This shell is considered an exoskeleton and serves to protect itself. It is unlike us, instead of having the bones on the inside, they have them on the outside. In gastronomy, crab meat is quite in demand and this means that its existence may be threatened.
In this article we are going to tell you the characteristics and way of life of the crayfish to know it better.
Key features
The exoskeleton that covers it is quite hard and serves to protect it. It is composed mainly of Calcium. Its entire body is fragmented into portions that allow it to move and navigate around the river. The main portions are the anterior and posterior portions, also called cephalothorax y abdomenThe anterior part contains the head and thorax, separated by the cervical groove. On the other hand, the carapace is extended into a space where the eyes are inserted. Its mouth is located on the ventral part of the head and is surrounded by legs that assist in movement.
The native crayfish is found in rivers throughout the peninsula and is usually easily distinguished as it has 5 pairs of legs on the sides and ventral area of ​​the cephalothorax. The first pair of legs has tweezers Quite developed, these claws are used both for defense and for capturing food. It is perhaps this claw that makes crabs distinctive and for which they are famous. The next two pairs of legs also have claws, but they are much smaller than the first. The first pairs are the most important and useful for the animal. The last two pairs of legs have a claw that they use for proper grip and stability when moving. All pairs of legs are used for movement except the first, which is always ready to defend itself or attack prey.
In addition to the above, it is convenient to place it taxonomically: it belongs to the class Crustacea, subclass Malacostraca, order Decapoda and family AstacidaeIn Western Europe, the best-known native representative is Austropotamobius pallipes, of variable coloration with tones olive green, brown or gray, and with males that are usually somewhat larger than females. Adult individuals can reach around 12 centimeters of body length not including the pincers, although there is variability depending on the population and environmental conditions.
The anterior part of the shell is extended by a face on the sides of which the compound eyes are inserted. The head also bears the antennas y antennules and several specialized mouthparts (maxillae, maxillae, and maxillipeds) that manipulate and select food. The chitin of the exoskeleton is reinforced with calcium carbonate, which gives it strength, but forces the animal to perform dumb periodic to grow.
Body functions
The antennae are arranged at the end of the face and also have some smaller antennae. These antennae serve as the organ through which they adapt to the environment and have sensory function. It also helps maintain balance and sense everything around them. The antennules contain specialized sensory structures and the statocyst, which is key to spatial orientation.
The respiratory system works thanks to a few gills which has two chambers that are arranged on both sides of the cavity that has the cephalothorax. These finely branched gills are protected by the shell and are irrigated by the hemolymph, which allows for efficient oxygen exchange even in relatively cold waters. Its abdomen has six flexible segments and each has a pair of appendages. These appendages are the pleopods, biramous and, in the last segments, very developed. In the segment at the end of the on the phone There is a powerful swimming caudal fin. This makes the crayfish a good swimmer, allowing it to move easily even in stronger river currents.
The crabs' capacity must be sufficient to survive in environments where the water current is strong. For example, during heavy rains, the river flow increases and the crabs must be prepared to survive in these situations. To escape, they perform rapid backward swimming propelled by the fan of the flow, while for fine movement they combine movements of their pereiopods with support on firm substrates.
As for the digestive system, it is very discreet. From the outside, only the anus, which is on the ventral part of the telson, can be seen. Internally, they have a molar stomach with calcified plates that grind food, followed by a glandular stomach and a relatively short intestine. The hepatopancreas is involved in digestion and the storage of reserves.
In order to differentiate male and female crabs, it is necessary to establish some differences between the sexual orifices. In males, these orifices open in the basal parts of the last legs, and the copulatory organ is located in the first two pairs. In females, the sexual orifices are found in the third pair of legs, and the others are either reduced or absent. Furthermore, females have pleopods adapted to the incubation of eggs, which are kept fixed under the abdomen by adhesive secretions.
Natural habitat
The crayfish is not very demanding in terms of the conditions it needs to live. It lives in all Spanish rivers with sufficient flow. Although it is not very demanding, it does prefer waters rich in salts. Calcium to be able to strengthen their exoskeleton and amounts of dissolved oxygen between 3 and 12 mg/l. As for temperatures, they need to be within a range of 8,5 and 22 degrees.
Crayfish serves as a good environmental indicator of the quality of the water in our rivers, since if they are contaminated we will not see them. Although they can withstand some strong currents, we mainly see them distributed in areas where the water speed is very slow. The river bottom can change and be located in both shallower and deeper places. They prefer shallow bottoms. record and pebbles with cavities, but also uses roots, trunks and margins under scouring.
It doesn't like brightly lit areas, so it takes advantage of hiding in river vegetation. Sometimes, it can dig a hole with its claws if it feels threatened. It can also hide in bank slopes or under larger stones. Peak activity occurs at night where the light prevents it from being discovered by its prey. It is most active between spring and autumn; the rest of the year, it hibernates in one of its most frequent safe hiding places.
As for its distribution, the native European crab is present in Western Europe with historical populations in numerous rivers and streams of the Iberian Peninsula. In island systems and isolated reservoirs it may lack direct natural competitors, although the presence de peces and opportunistic birds can modify their behavior and shelter patterns.
Feeding and reproduction of crayfish
These crabs eat almost everything. Include in your diet little fishes, carrion of other animals, amphibian larvae, macroinvertebrates, aquatic plants and even seaweedAmong the most important predators that must be protected are coleopteran and odonate insects, other larger fish, birds, and some mammals such as the otter. In some reservoirs with introduced fish, species such as tents and cyprinid predators may consume juveniles or compete for resources; the eel, when present, is one of the potential native predators.
The crayfish travels along the bottom consuming organic remains and live prey, acting as omnivore and as a recycler of matter. This flexible diet allows it to exploit different microhabitats. Its feeding rhythm intensifies at dusk and at night, when it reduces the risk of being detected by birds and other visual predators.
As for its reproduction, the reproductive period begins before hibernation in which the female is able to place between 40 and 80 eggs under the abdomen and attached to its legs. It protects it while they hibernate until the eggs hatch the following spring. In larger females or in populations with optimal conditions, the number can approach 100 to 150 eggsThe juveniles initially remain attached to their mother until they undergo their first moults and gain mobility.
Its development and growth is carried out through dumb, in which the crab sheds its shell or exuvia, increasing in size. This process is repeated five or six times during the first year. The number of molts subsequently decreases, typically concluding with two molts in males and one in females during adulthood. Sexual maturity is usually reached between 2 and 4 years, influenced by temperature and food availability. The average longevity is around 6 to 8 years, although there are specimens that can exceed this figure under favorable conditions.
Reproductive mating usually occurs in late autumn and the female maintains laying eggs throughout the colder months. hatching It is concentrated between late spring and early summer, when the temperature stabilizes embryonic development and increases the availability of food for the young.
Similar species and how to differentiate them
In the rivers you can see exotic crabs that are confused with the native crab. Recognizing them is key to campaigns and to communicate findings to the authorities:
- Native crayfish (Austropotamobius pallipes): rough-textured pincers with the ventral side whitish and the same light shade on the ventral side of the legs. The carapace has two separate longitudinal lines. Coloration varies from brown to greenish-gray, sometimes with bluish hues.
- Red crab (Procambarus clarkii): very tweezers thorny, with marked roughness and, in many specimens, tonality wine red. It has a noticeable spur on the wrist of the claw. The lines on the carapace are usually joined or very close together.
- Signal crab (Pacifastacus leniusculus): shows a feature whitish spot at the base of the claws, hence its name. Large and powerful claws; dorsal surface relatively smooth and ventral surface with reddish tones. Two longitudinal lines of the carapace somewhat separated; the ventral surface of its claws tends to be red.
Other occasional species in Europe, such as astacus astacus, Astacus leptodactylus u Orconectes limosus, are recognized by details of the face, the shape of the claws or the presence of spurs, but the two exotic species with the greatest expansion in the peninsula are the red crab and the signal crab.
Ecological interactions and behavior
The crayfish is a species omnivore Broad-spectrum. At the trophic level, it plays an intermediate role: it preys on invertebrates and amphibian eggs or larvae, consumes detritus, and cleans the bottom of debris, while also serving as food for fish, birds, and mammals. In some reservoirs or areas with introduced fish, carp and other cyprinids may influence its behavior and the availability of shelters by removing the substrate.
The presence of predators determines their time and type of shelter. Herons, otters and certain rodents Opportunistic predators capture it when it is active or during its molt, when it becomes more vulnerable. In island or isolated systems, the lack of some natural predators or competitors can favor high densities, although this depends on the flow regime and habitat structure.
Conservation, threats and legal framework
The main historical threat to the native crayfish on the peninsula has been the afanomicosis, a fungal disease caused by Aphanomyces astaciThis pathogen, associated with the introduction of exotic crabs, causes high mortality rates and has contributed to the decline of many populations. Added to this are other pressures: canalization, prey and flow regulation, contamination of water, illegal extraction and loss of riparian habitat.
Exotic species such as Procambarus clarkii y Pacifastacus leniusculus not only compete for resources and shelters, but are also reservoirs of the afanomicosis fungus. Therefore, measures to biosecurity The following are essential: disinfecting fishing equipment, not releasing specimens or using live bait, and avoiding translocations. Breeding and population reinforcement programs, along with improving water quality and river connectivity, are common lines of action for their recovery.
In the regulatory framework, the native crayfish is considered Vulnerable in the Spanish Catalogue of Endangered Species. In large areas it is not fishable and their capture is prohibited. Some autonomous communities protect them with stricter categories and maintain breeding centers and river reserves. If you see any exotic animals or die, it is recommended that you report them to the relevant environmental authority.
Optimizing crayfish conservation involves a comprehensive approach: restoring riverbanks and substrates record, restore ecological flows, maintain riparian vegetation that provides shelter, control exotic species, strengthen surveillance, and promote environmental education. Citizen participation, through participatory science and compliance with regulations, is key.
Know your biologyRecognizing exotic species and appreciating their ecological role helps protect this unique freshwater decapod, a discreet protagonist of our rivers and a true bioindicator of their health.
