Crabs and lobsters, they both have pincers, lots of legs and tough outer shells. Both are caught for seafood. But what is the difference between these two decapods?
What is a decapod?
Decapods are a group of crustaceans that include crabs, lobsters and shrimp. There is thought to be around 15,000 species of decapod worldwide. They live in a wide diversity of aquatic habitats from freshwater and semi terrestrial to marine. A key member of the marine food chain, thanks to their direct impact on habitat structure, fish populations, presence of algae and prey availability.
What does decapod mean?
Decapod means ten footed – therefore 10 of the appendages, or five pairs of appendages, on these creatures are considered legs, which are scientifically known as pereiopods.
Many decapods, including the common shore crab and European lobster have enlarged pincers called chelae. These enlarged claws/ pincers are used for protection, communication, attracting mates and gathering food.
What is a crab?
The common shore crab, Carcinas maenas, is the most common crab encountered on UK shores. It is generally a green-ish colour but sometimes may be more orange or red, the pincers can often be orange-red. If you’re struggling to identify it from colour and size, shore crabs have five up turned spikes on each side of its carapace (main shell) as well as three rounded lobes between the eyes. The shore crab can be found from 1cm wide up to a carapace of around 9cm wide.
These crabs are easily found in rockpools, in the shallows, or in the strandline after high tide.
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What is a lobster?
The European or common lobster, Homarus gammarus, have long bodies, big front pincers and a wide tail. They have one pincer larger than the other, one used for crushing and one for tearing.
The average length of a fully grown common lobster that is caught in the UK is around 30cm but they can easily reach up to 60cm long and have been known to be 1m long.
Common lobsters can be a variety of colours, but typically are a deep blue/ black colour with red antennae and orangish pincer tips.
The antennae along with the limbs, are used to learn information about the environment by detecting vibrations and chemical signals in the water.
Lobsters grow by shedding their hard exoskeleton which is known as moulting. The larger the lobster gets, the less frequently it moults. Common lobsters can live for around 50 years.
Where are lobsters and crabs found?
Here in the UK you’re most likely to spot crabs down at the beach, the most common species being the shore crab. Although, you may sometimes see the impressive spider crab or edible crab. Shore crabs are robust and may be found on rocky shores, sandy beaches and estuaries. Other crab species may also be found in freshwater ecosystems.
European lobsters are not something you’re likely to stumble across in rockpools on your beach walk. They stay out at sea, known as bottom dwellers, living on shallow sea floors in rock cervices and hidey-holes.
They are caught by fisherman for seafood delicacies. Lobster fishing has laws around it – if a lobster under a certain size is caught in a pot the fisherman must return it to the sea. Similarly, if a pregnant female (berried lobster) is caught, this must be released.
What do crabs and lobsters eat?
Both crabs and lobsters sense the world through hairs on their body which are sensitive to touch, sound, smell, taste and temperature.
They use their oversized front claws to break into hard shelled creatures like mussels, cockles and other crustaceans such as smaller crabs and prawns. They will also take small fish or squid if they come close enough to catch. They also scavenge, meaning they take dead or dying creatures already on the seabed floor.