Crustacea

Crustacea – Lobsters, Crabs, Prawns, Shrimps and Barnacles

• The Common Lobster (Homarus vulgaris) occurs in deeper water below the low tide level around the Irish coast. A relative of the crabs and shrimps, lobsters have no bones in their bodies but instead rely on a hard ‘exo-skeleton’ like a suit of armour, that has to be sloughed off and regrown as the animal gets older and increases in size. Lobsters are fished all around the Irish coastline using baited pots and experiments have been conducted to try and repopulate areas where lobsters are scarce using juvenile lobsters raised in specially built lobster hatcheries.

Nephrops Lobster

The Nephrops Lobster is also known as the Norwegian Lobster or the Dublin Bay Prawn. Despite its name, it is not found in Dublin Bay. Nephrops Lobsters are found however in the Irish Sea and off the west coast of Ireland. They can grow up to 8cm in length.

©Michael Viney

Nephrops Lobster
©Michael Viney

Nephrops Lobster

The Nephrops Lobster is also known as the Norwegian Lobster or the Dublin Bay Prawn. Despite its name, it is not found in Dublin Bay. Nephrops Lobsters are found however in the Irish Sea and off the west coast of Ireland. They can grow up to 8cm in length.

©Michael Viney

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• The Dublin Bay Prawn (Nephrops norwegicus) lives in deepwater in soft mud where it can create burrows to hide in. Fisheries for Dublin Bay Prawn can be found in many places around the Irish coast including Galway Bay, the Aran Islands and in the Irish Sea.

• The Common Prawn (Palaemon serratus) is completely transparent and has a long serrated ‘rostrum’ that projects forward between its eyes like a spike. Prawns are very common on rocky shores, particularly if there are rock pools for them to hide in at low tide. Their powerful tail can flick forwards suddenly to propel them back out of harm’s way if they are attacked.

• The Common Shrimp (Crangon crangon) is likely to be found in soft sand where it can wiggle down and bury itself easily. Unlike the Common Prawn, it is speckled in many shades of yellowy brown to hide itself in the sand.

Velvet Crab

The Velvet Crab is usually found in shallow waters of rocky shores or in rock pools.

Taken by Kieran Boyce, Dublin University Sub-Aqua Club

Velvet Crab
Taken by Kieran Boyce, Dublin University Sub-Aqua Club

Velvet Crab

The Velvet Crab is usually found in shallow waters of rocky shores or in rock pools.

Taken by Kieran Boyce, Dublin University Sub-Aqua Club

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• Common Shore Crabs (Carcinus maenas) are abundant on all rocky shores and can be found easily in rock pools, under rocks and seaweed. They have two powerful claws that they use to defend themselves and to catch food, as well as a hard shell with a serrated edge. Like lobsters, crabs must discard their shells as they grow and then hide until the new one hardens. This is why you can sometimes find ‘soft’ crabs on the beach that have not yet hardened up.

• The Edible Crab (Cancer pagurus) is fished around the Irish coast at many ports, particularly in Wexford, Galway and Donegal. It is found in deeper water below Irish beaches, although young specimens can sometimes be found sheltering under rocks at low tide. The Edible Crab is brick red or brown in colour with a distinctive ‘pie crust’ edge on its shell and two powerful claws.

• Hermit Crabs (Pagurus bernhardus) do not have complete shells of their own but ‘borrow’ the empty shells of whelks and winkles to protect their soft tails. They are found at middle and lower shores around Ireland and may sometimes even share their ‘rented accomodation’ with a rag worm that lives inside and a sea anemone that fixes itself to the top.

Barnacles

The rocks at this rockpool are covered in barnacles

Barnacles

Barnacles

The rocks at this rockpool are covered in barnacles

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• The Common Barnacle (Semibalanus balanoides) resembles a tiny white volcano with double doors. In reality it is a kind of crab that lives on its back inside a chalky shell and uses its legs to grab food from the passing water, rather than run around chasing after it. Barnacles, of different species are found from the lower shore to the splash zone along rocky coasts.

• Sandhoppers (Talitrus saltator) are found in huge numbers on rocky shores, sheltering under the dead seaweed at the top of the beach or under rocks further down. By night, they come out to feed on seaweed and can be heard jumping about by means of their powerful tails, sometimes leaping quite long distances.