Short description of Hemigrapsus takanoi, Brush-clawed crab

A small crab with a square carapace up to 25 mm wide, with three lateral spines on each side.  Variable colour; commonly dark grey-green to brown-orange, banded legs and tiny dark spots on parts of the body and pincers (never on the abdomen).  Males exhibit a yellow-brown fuzzy growth at the base of the pincers. 

Impact summary: Hemigrapsus takanoi, Brush-clawed crab

The brush-clawed shore crab may compete with native crabs including the common shore crab for space and food.  Where it occurs in high densities this crab has been reported to dominate native crab species; in France and the Netherlands it is reported to dominate the shore crab Carcinus maenas.

Habitat summary: Hemigrapsus takanoi, Brush-clawed crab

The brush-clawed shore crab inhabits muddy sediment in the intertidal areas of mudflats, estuaries, harbours, lagoons and sheltered bays.  It tends to occupy low energy, sheltered sites and is found under boulders and other hard structures. 

Overview table

Environment	Marine
Species status	Non-Native
Native range	Northwestern Pacific
Functional type	Predator
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	Colne Point
Date of first record	10

Origin

The brush-clawed shore crab is native to the western Pacific Ocean, from northern Japan and some areas of Russia’s Pacific coast to China.

First Record

The brush-clawed shore crab was initially mistakenly identified as the sibling species Hemigrapsus penicillatus at La Rochelle on the Atlantic coast of France in 1994.  In the English Channel it was first reported in Le Havre in 1997.  First recorded in the UK in 2014 from the River Medway, Kent and the River Colne, Essex

Pathway and Method

Brush-clawed shore crabs are thought to have been introduced to European waters in their larval form through discharge of ships’ ballast water.  Further introductions and spread may have occurred unintentionally with transportation of oysters for aquaculture, or associated with hull fouling communities.  Natural range expansion following initial introductions occurs when pelagic larvae are dispersed by currents.  

Species Status

Since initial records in La Rochelle, France in 1994 the brush-clawed shore crab has been reported in increasing numbers on French, Spanish, Belgian and Dutch coasts.  It is now present along approximately 1,000 km of coastline from the western part of the Bay of Seine in France to Lower Saxony in Germany, and is common in at many sites within this area. 

Dispersal Mechanisms

The larvae are planktonic (free swimming in the water column) for up to one month.   During this period, before the larvae develop into juvenile crabs, they may be transported considerable distances by currents.  Larvae may also be transported in ships’ ballast water, being released into harbours or bays.

Reproduction

Little information specific to the brush-clawed shore crab was found.  However, sibling species H.penicillatus can produce up to 50,000 eggs up to six times over its 8 month reproductive period. One batch of sperm may fertilize successive batches of eggs.  Once hatched, larvae are planktonic for up to one month, and growth and maturation are rapid. 

Known Predators/Herbivores

Potential predators would include some bottom feeding fishes, birds and other crabs. 

Resistant Stages

None known.

Habitat Occupied in GB

Not currently known in GB, however suitable habitats are widespread around GB coasts. 

The native range stretches from northern Japan, some regions of Russia’s Pacific coast, Korea, China and Hong Kong. Since initial records in La Rochelle, France in 1994 the brush-clawed shore crab has been reported in increasing numbers on French, Spanish, Belgian and Dutch coasts.  It is now present along approximately 1,000 km of coastline from the western part of the Bay of Seine in France to Lower Saxony in Germany, and is common in at many sites within this area.  First recorded in the UK in 2014 from the River Medway, Kent and the River Colne, Essex. In 2016, the species was recorded as very abundant in the River Orwell, Suffolk. 

Environmental Impact

On a Dutch shore where the brush clawed shore crab has reached high densities, a drastic reduction in the number of juvenile native common shore crabs has been observed.  Similarly in Dunkirk harbor this species appears to have replaced the common shore crab as the dominant and most abundant shore crab species.  A similar impact on native crabs may occur were the brush-clawed shore crab to become established in GB.

Health and Social Impact

None known.

Economic Impact

None known.

Identification

Asakura, A. & Watanabe, S. (2005) Hemigrapsus takanoi, new species, a sibling species of the common Japanese intertidal crab H. penicillatus (Decapoda:Brachyura:Grapsoidea). Journal of Crustacean Biology, 25, (2), 279-292.

D’Udekem d’Acoz, C. (2006) First record of the Asian shore crab Hemigrapsus sanguineus (De Haan, 1835) in Belgium (Crustacea, Brachyura, Grapsoidea). De Strandvlo, 26, (3), 74-82.

Biology, ecology, spread, vectors

Dauvin, J-C., Tous Rius, A. & Ruellet, T. (2009) Recent expansion of two invasive crab species Hemigrapsus sanguineus (de Haan, 1835) and H.takanoi Asakura and Watanabe 2005 along the Opal Coast, France. Aquatic Invasions, 4, (3), 451-465.

Mingkid, W.M., Akiwa, S., & Watanabe, S. (2006) Morphological characteristics, pigmentation, and distribution of the sibling penicillate crabs, Hemigrapsus penicillatus (De Haan, 1835) and H. Takanoi Asakura & Watanabe, 2005 (Decapoda, Brachyura, Grapsidae) in Tokyo Bay. Crustaceana, 79, (9), 1107-1121.

Pillay, K.K., & Ono, Y. (1978) The breeding cycles of two species of grapsid crabs (Crustacea: Decapoda) from the North Coast of Kyushu, Japan. Marine Biology, 45, (3), 237-248.

Management and impact

Dauvin, J-C. & Delhay, J-B. (2010) First record of Hemigrapsus takanoi (Crustacea: Decapoda: Grapsidae) on the western coast of northern Cotentin, Normandy, western English Channel. Marine Biodiversity Records, 3, 1-3.

General

Asakura, A. & Watanabe, S. (2005) Hemigrapsus takanoi, new species, a sibling species of the common Japanese intertidal crab H. penicillatus (Decapoda:Brachyura:Grapsoidea). Journal of Crustacean Biology, 25, (2), 279-292.

Wood, C. A., Bishop, J. D. D., Davies, C. J., Delduca, E. L., Hatton, J. C., Herbert, R. J.H. and Clark, P. F., 2015. Hemigrapsus takanoi Asakura and Watanabe, 2005 (Crustacea: Decapoda: Brachyura: Grapsoidea): first records of the brush-clawed shore crab from Great Britain. Bioinvasions Records 4 (2), pp. 109-113.