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Shore crab

size:

carapace up to 9 centimeters wide

color:

green to dark grey; legs green or red

age:

3 to 5 years

food:

omnivore: plants, worms, fish, carrion, other crustaceans, shellfish (particularly mussels)

enemies:

gulls, other bird species, some fish

reproduction:

sexual

  • Dut: Strandkrab
  • Lat: Carcinus maenas
  • Eng: Shore crab, European green crab
  • Ger: Strandkrabbe (Gemeine Strandkrabbe)
  • Dan: Almindelig strandkrabbe
Shore crab, foto fitis, sytske dijksen

Shore Crab

Shore crabs, also known as green crabs, are the crabs you find the most along Dutch shores. They are native to the North Sea, but have managed to spread throughout the world in a very short time. Due to the invasion of European shore crabs in American waters, this species is listed number 18 out of the 100 most damaging intruders in the world. You don't have to search for long to find one if you're by the sea. Birds don't have to wait long either; during low tide, lots of crabs are eaten. The crab itself thinks it can handle its enemies and will courageously try to pinch your fingers or toes should you encounter one. Shore crabs are the 'garbage collectors of the sea'; they eat whatever is dead or sick. On the tidal flats, they eat all sorts of benthic animals.

  • Distribution and habitat
    mating shore crabs, foto fitis, sytske dijksen

    Shore crabs are very common in the North Sea, Wadden Sea and delta regions. In the summer, they hunt on the tidal flats and migrate to warmer deeper waters in the winter. During low tide, you can see them walking over the sea floor, sideways of course. You also have a good chance of finding them by tilting up a large stone, where they hide during low tide.

  • Softshells

    Due to their hard shell, crabs can't grow larger very easily; the shell doesn't stretch well at all. A crab needs to shed is carapace in order to grow. In preparation, they recycle part of the old carapace and use it to start growing a new one. They then literally step out of their old carapace. Because they absorb lots of water during the process, they grow in size in one fell swoop. Their new carapace then hardens with lots of space to grow. The extra moisture is eventually replaced with new tissue, until they once again literally explode out of their carapace.

    In their first year of life, green crabs molt up to 7 or 8 times. The amount of moltings decline in the years that follow; eventually, they molt an average of once a year.

    When a crab first gets a new carapace, it is very weak and easily damaged. These crabs are referred to as softshells. The animal must find shelter to avoid being caught by predators. During this stage, crabs are able to regenerate missing legs and claws. You can always see if a crab has new appendages: they are never as long as the original ones.

    Crabs whose shells start to stiffen are called papershells. When the carapace has stiffened even more, but is still pliable, the crab is called a buckram.

    Around the time when the female molts, the male will mate with her and then carry her under his body for a couple of days until her carapace has hardened up to a buckram stage. He doesn't want her caught by a predator and see his efforts go to waste!

  • Hitchhikers
    Shore crab with barnacles, foto fitis, sytske dijksen

    Should you find a crab on the beach take a good look. There is a good chance you will see more than just a crab. Other animals often use the crab to get around, such as mussels, barnacles or bryozoans. Usually, these hitchhikers don't get a chance to affect the crab - by molting, the crab gets rid of them.

    Older crabs do not shed as often, so that the lifters have the opportunity to grow quite large. Then they can get in the way when moving around. Walking around with a coat of mussels and barnacles costs a lot of energy. There are even incidents known where barnacles grow in the eyehole of the crab. Barnacles grow fast and can push away the crab's eye, blinding it. Slow and blind crabs make easy prey for birds and fish. So when hitchhikers grow large, it often means the end is near for the crab.

    Another organism found in shore crabs is a parasite call Sacculina carcini. This parasite uses the crab not only to live in, but eats its food and makes it impossible for the crab to reproduce. You recognize an infected crab by the sack it carries under its tail. Crabs carrying this parasite are doomed.