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Uniramia (Insecta)

British Marine Life Study Society

Shore Crab

The crab is examining a Dogwhelk, NucelLapillus, a gastropod that is rarely eaten because the shell is too thick for the claws to crack.
Common Name(s):
Shore Crab
European Green Crab, Applejacks (Newhaven, Sussex), Addlers (Shoreham, Sussex) 
Scientific Name:
Carcinus maenas
Usual Size:  to 6 cm 
 (length of carapace)
 width to about 10 cm 
  up to 149 grams 
   (see note)
        Photographs by Andy Horton
Medium sized. Carapace broader than it is long. Two powerful claws. Rear legs pointed for gripping on to rocks. 
Colour: Brown.  Some specimens about 5% of adults are green. Juveniles in a mixture of colours.

Juveniles are often patterned like this one from Penllech Beach on the Lleyn Peninsular
Photograph by Matt Amos

20 August 2020

Fifty mostly adult Shore Crabs, Carcinus maenas, were attracted to the chicken bait in small drop-nets in under an hour from the Toll Bridge at high tide on a sunny afternoon.


Similar species:  Velvet Swimming Crab,  Necora puber.

Eggs released during the spring mostly, but crabs 'in berry' present in all months. Young particularly abundant on the shore in June. 

    Crabs prior to mating. The female crab is underneath.

    Shore Crabs, Carcinus maenas

    Shore Crabs, Carcinus maenas
    Crabs prior to mating. The female crab is underneath
    Photograph  ©  by Chris Rowe

    Male Shore Crab  (photograph by Andy Horton)In the female the flap is much broader to carry the eggs

    Male Shore Crab

    The large flap (broader abdomen) of the female crab used to hold the eggs

    The large flap (broader abdomen) of the female crab used to hold the eggs

More photographs (external site)

Abundant intertidally in spring, and present on the shore throughout the year.  Estuaries and brackish water, rivers, during the summer only. Most widespread of all medium-sized British crabs 
Parasitic barnacle Sacculina carcini 
Worms. Mollusc flesh, small gastropods, small crabs, algae, carrion and almost anything it can catch. 
(The top photograph shows this crab examining a Dogwhelk, Nucella lapillus, a gastropod that is rarely eaten because the shell is too thick for the claws to crack.) 
In October 1999, a medium-sized Shore Crab was observed eating  a young (first year) 30 mm Rock Goby, which were frequent under rocks on Kingston beach
All British coasts. 
Natural distribution further afield: Norway to Mediterranean and tropical Atlantic coast of North Africa. 
Naturalised: as expected for such a hardy crab, it has spread across the Atantic to the American side, and probably further afield. I would not be suprised to see it spread to the southern hemisphere as an unwelcome addition. It could displace native crabs in estuaries and the adjacent seas and coasts. 
Temperature amplitude: 4 - 28° C (and greater). 
Alien Invader:
C. maenas, or European Green Crab (Shore Crab??) has slowly been making its way northward along the pacific coast of the US for the past decade or so.  C. Maenas was spotted in Washington state (northwest corner of cont. US) just a few years ago, and the ecology of that area is such that it could decimate Washington's mollusk and oyster populations if it establishes itself.            David Scripps (Minnesota).

Enemies:  anything that can swallow it, depending on size and location. 
In the English Channel they are eaten by Bass and gulls, Laridae.  Not larger crabs usually. 
In June, in the River Adur estuary, Sussex, England, the juvenile crabs are at their maximum numbers. 
They often get into fights with its own kind. It may lose claws in these fights, and many (up to 5%) adult crabs on the shore have missing claws or smaller claws regrowing. 

Additional Notes:
Why do crabs walk sideways?
Moulting cycle in Crustacea
Only in fresh and brackish water during the summer when the water temperature is warmer. Unable to osmoregulate in the colder winter water and the crab returns to the fully saline sea. 
In summer, the crab likes to leave the water (rocks above the waterline in aquaria) and take in atmospheric oxygen. It is a great escape artist in captivity. 
Assimiliation of Oxygen at different temperatures (Ref.)

5 November 2009
On a high spring tide, a Little Egret was observed fishing in the shallow water and capturing a morsel every three minutes or so. At a distance itwas difficult to see what it was actually capturing in its long black beak, but on at least two occasions it looked like small Shore Crabs, Carcinus maenas, that tried to wriggle out of its beak without success. 

20 June 2005
Shore Crabs, Carcinus maenas, were observed dying in isolated pools in Widewater Lagoon

Report by Derek Neate (FOWL)
With the low level (0.27 metres) of the lagoon, the patch of water by the inlet pipe became isolated from the main body of water. In this puddle the salinity was recorded at a hypersaline 42.8 after two weeks of warm weather (air temperatures over 24° C and over 27° C) and a water temperature of 30.2° C. The main body of the lagoon registered a salinity of 37. (The conditions were favourable for evaporation.)
Readings by John Knight (WSCC)
These two events are probably connected. In June (in Sussex) the Shore Crab moves in estuaries and into lower salinity water than the sea. In water temperatures of over 28° C or with a salinity over and above natural seawater at about 34.5 this crab has been known to leave the water and perish if it is unable to find a favourable niche. (The conditions are outside its natural amplitude for survival.)

2002 and earlier
Edible Crabs, Cancer pagurus  will attack and kill Shore Crabs in aquaria and they will occur together in the wild.
Lobsters, Homarus gammarus, will quickly kill and eat Shore Crabs in captivity. They will meet occasionally in the wild, but not all that often. 

16 July 1999
Carcinus maenas were present in small numbers at Goring (near Worthing), West Sussex,  including a couple carrying the parasitic barnacle Sacculina carcini.

Report by Chris Everson
Photograph by Ray Hamblett

Katherine Hamblett at Adur World Oceans Day 2000

The female Shore Crab in the picture called "Sandy" weighed 78.81 grams alive on 20 June 2000. The carapace measured 70.61 mm wide. (Imperial 2.78 oz, 2.78 in.). It died about a year later without moulting. 

Each year in the delightful coastal village of Walberswick in Suffolk, The British Open Crabbing Championship is held.

Largest Crabs

The heaviest crab known was the winner of the Walberswick Crabbing competition in 1981 which weighed in at 7.25 oz (205.5 grams).  Crabs of over 3 oz are caught every year, crabs of over 4 oz are prize winners and crabs of 5.25 oz have been caught. The second heaviest Walberswick Shore Crab was caught on 6 August 2000 and weighed nearly 7 oz

Message-Id: <v0422080bb647c7b02dcd@[]>
Date: Mon, 27 Nov 2000 09:52:56 +0100
From: Per-Olav Moksnes <>
Subject: [CRUST-L:561] Summary: Carcinus max-size

Thank you to all who responded regarding the maximum size in Carcinus maenas.

I have not yet received any reply that confirms that a Carcinus larger than 100 mm CW has been collected.

Greg Jensen from University of Washington reported that Carcinus close to 100 mm CW have been caught in Bodega Harbor, California (the largest confirmed was 96 mm). Wim Vader from Tromsø Museum in Norway believe Carcinus grow larger than 100 mm in northern Norway, but it has not been possible to confirm this yet.  I also heard some rumors 
about very large Carcinus in Southern Australia, but I have had no replies from down under.

A quick look through the literature produced the following list of unusually large Carcinus:

Location  Reference   Max CW

Denmark   (Munch-Petersen 1982):  75 mm
New England, USA (Ropes 1968):   80 mm
California, USA  (Cohen 1995):   85 mm
Australia  (Zeidler 1988)   85 mm

Thus, the 100 mm CW beast caught in Sweden last month appear to be the largest reported Carcinus maenas.

Per-Olav Moksnes, Ph.D.
Department of Marine Ecology
Göteborg University
Kristineberg Marine Research Station
S-450 34 Fiskebäckskil

Maximum quoted size = 86 mm carapace breadth [which doesn't sound very big 
to me, 3.4" in imperial units - Pete], but usually less. Terminal ecdysis can be any time from ~60 mm. (from 'Biology of the Shore Crab')

Messages on Sizes

Field Studies Council Publications
The Field Studies Council publish a special booklet on the Shore Crab. 
They also publish an excellent guide called "A Key to the Crabs and Crab-like Animals of British Inshore Waters" by John & Marilyn Crothers. ISBN 1 85153 155 5

"The Biology of the Shore Crab Carcinus maenas (L)" by J.H.Crothers
 1. The Background - Anatomy, Growth and Life History - reprinted from Field 
Studies vol 2, no.4, pp 407-34 (1967)
 2. The Life of the Adult Crab - reprinted from Field Studies vol 2, no.5, 
pp 579-614 (1968)

From: Field Studies Council, Preston Montford, Shrewsbury SY4 1HW

Information wanted: Please send any unusual records of this crab, with location, date, who discovered it, how it was identified, prevalence, size, whether 'in berry', common name and any other details to 
Shorewatch Project    EMail
All messages will receive a reply. 

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