sea urchin

Common sea urchin

Latin name: Echinus esculentus
Global Distribution: Abundant in the N.E. Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Absent from the Mediterranean.
UK Distribution: Common on most coasts of the British Isles but absent from most of east coast of England, the eastern English Channel and some parts of north Wales.
Size: Circa 4 to 11 cm depending on age
Diet: Algae and encrusting invertebrates
Habitat: Found on rocky substrata from the sublittoral fringe to circa 40 m, although it may be found at depths of 100 m or more

The common sea urchin can occupy an impressive depth range, starting from the intertidal zone and going down to 1,200 m! Another common name for this species is the edible sea urchin, so called because it is eaten by humans around the world. Specifically, we eat their gonads (reproductive organs). It is actually considered “Near Threatened” in the IUCN Red list of Threatened species and this is partially due to over-exploitation.

The common sea urchin is considered a key species for sub-tidal rocky areas, regulating the levels of encrusting animals and algae. They are very active grazers and can clear rocks back to bear allowing new animals or plants to settle. They can also be very destructive if the population gets out of balance and they “over-graze” areas. They have tube like feet that they use to swiftly move around or to hold on rocks when necessary. The mouth is located at the underside of the urchin and is equipped with 5 specialised plates which act as a jaw and are known as “Aristotle’s lantern”. The history has it that Aristotle, a Greek philosopher and naturalists compared the mouth’s shape with a “horn latent”, as in his time lanterns were made out of horns and had 5 sides.

Fun facts

  • During spawning, females can release around 20 million eggs into the water.
  • They may have associated animals living among their spines, such as the worm  Adyte assimilis and the copepod Pseudoanthessius liber, which benefit from living on the sea urchin, but do not benefit, or harm, their host.
  • A study in Scotland found that salmon farm feeds can enhance the growth of their gonads, which can increase their value for human consumption.