How did humans discover that crabs are edible

Carcinus maenas Common beach crab

Characteristics

What do common beach crabs look like?

The common beach crab belongs to the crustaceans and there to the order of the decapod crabs. As with all crustaceans, their bodies are surrounded by a hard shell called an exoskeleton. The head and back are covered by a continuous shield, the pentagonal armor. The two stalked compound eyes sit on the forehead on the head. They can be folded into the eye pit for protection. Two short antennae sit between the eyes, with which the crabs can feel and smell.

The five pairs of legs are typical. The first pair has been converted into powerful scissors. One pair of scissors is bigger than the other, they are called snap scissors. The smaller scissors are called pincer scissors. The other four pairs of legs serve as walking legs. The abdomen, which is designed as a tail, is usually not visible because it is small and tucked under the body. The back shield is up to eight centimeters wide, together with the legs, the animals measure up to ten centimeters. The males are slightly larger than the females. You can also recognize them by their pointed abdomen, the females by their rather round abdomen.

Because of its hard shell, the beach crab, like all crustaceans, can only grow by shedding its skin: the old shell bursts open. The crab then pumps itself up with water so that the new, still soft shell underneath is stretched. It takes about three days for it to harden. Sexually mature crabs moult only once a year, young ones more often. The top of the crab is usually dark green to grayish, the underside of the body is yellowish. If a crab is older or has not shed its skin for a long time, its back tends to be brownish in color and its belly becomes reddish.

Where do common beach crabs live?

Originally, the common beach crab was only at home on the Atlantic coast of Europe and North Africa and in the North and Baltic Seas. In the Baltic Sea, however, it only occurs as far as RĂ¼gen, further east it is absent. Because there the salt content of the water is too low for the beach crab. Because the common beach crab used to be transported in the wood of ships or in the ballast water of modern ships and is very adaptable, it is now also found on the east and west coast of North America and on the east coast of South America. It has even been spotted on the coast of South Africa and Australia.

The common beach crab is an inhabitant of the mudflats. This is the habitat on the seashore, which is characterized by ebb and flow: there the ground falls dry twice a day and is flooded again by the sea twice a day. The crabs live in this zone up to a depth of 60 meters, but mostly they stay in shallow water and near the shore. They are preferably found on coasts where the surf is not too strong. There they populate stands with sandy soil, rocks or silt.

What species is the common beach crab related to?

There are around 6800 different species of crabs worldwide. They occur predominantly in the sea, some also in fresh water, and a few on land.

A well-known relative of the common beach crab is the hermit crab. It also belongs to the decapods, just like the North Sea shrimp, the edible crab or the Chinese woolly crab.

How old do common beach crabs get?

The common beach crab can get amazingly old: It lives between five and ten years. How old the animals get depends, among other things, on the water temperature: the colder it is, the slower the crabs grow and the older they get.

behavior

How do common beach crabs live?

The first thing to discover on the beach is usually the empty back armor from. The tanks were repelled during the molting or come from dead animals. But with a little luck you can also observe live specimens: The beach crabs are particularly active at high tide and at night and then wander back and forth on the beach. They don't run forwards, but sideways, as is typical for crabs. They are lightning fast and can whiz across the beach at up to one meter per second.

If they don't wander into the deeper water at low tide, they look for a hiding place under seaweed and stones or in the sand. In these humid nooks and crannies, they can survive the ebb tide that lasts several hours on land. This is amazing, because beach crabs breathe through their gills. So that the gills are supplied with oxygen-containing water during this time, they carry a water supply in the gill chambers on the left and right under the armor of the back.

If a beach crab feels threatened, it stretches its claws towards the enemy, spreads them apart and collapses them threateningly. But the animals are not dangerous - neither for their predators nor for us humans. The best they can do is pinch our fingers. Beach crabs are not very friendly with one another: they may sit close together in their hiding places, but when they run into each other on the beach they threaten each other with their claws. The males even fight each other over who can mate with a female. But because they protect their armor, they rarely get injured.

Unlike other crabs, the common beach crab is not fished commercially. It is only eaten regionally in a few areas.

Friends and enemies of the common beach crab

The common beach crab has many enemies: it is a treat for seabirds, but it also eats fish and octopus. Despite claws and armor, the crabs hardly have a chance of survival against these enemies. They have no choice but to flee. However, the crabs have developed a clever survival strategy: if an attacker, such as a seagull, grabs them by one leg, they can throw it off and escape. Over time, the leg grows back as it sheds. If they lose the scissors in an attack, the weaker scissors are even converted into new scissors.

How do common beach crabs reproduce?

The Paarun takes place at different times depending on the region. However, the females can only mate if they have just moulted. After mating, they carry a large lump with up to 185,000 orange eggs on their abdomen until the larvae hatch. Depending on the water temperature, this can take up to four months. When the time comes, the females migrate into deeper water as the larvae move freely swimming. Ultimately, the larvae shed their skin several times and transform into tiny young crabs just one millimeter in size. These then live on the sea floor.

maintenance

What do common beach crabs eat?

The common beach crab is omnivorous. Their menu ranges from mussels, worms, sea urchins to small fish and other crustaceans. Even conspecifics fall victim to them, especially when they are still small or have just shed their skin. Nor do they stop at plants such as seaweed and even carrion. They break open the hard shells of mussels and crabs effortlessly with their cracking scissors. With the smaller pair of tweezers they cut up soft prey.

Because the common beach crab has a huge appetite, it is not welcomed as an immigrant on foreign coasts: The animals eat almost everything they can get their hands on and as a result, the number of other species native to them is declining.