Hemigrapsus sanguineus - Japanese shore crab

Hemigrapsus sanguineus originally lived only along the East Asian coast, from the Russian island of Sakhalin to Hong Kong. ^{[2, 3]}.

First observation in Belgium

The first sighting of the Japanese shore crab in the study area dates from the 13^th of August 2004, near Hoedekenskerke, in the Dutch part of the Western Scheldt. Here, three Japanese shore crabs were found on the pontoon of the ferry – among mussels ^[4]. In Belgium on the 20^th of July 2006 – on a breakwater in Knokke-Heist – a Japanese shore crab was caught for the first time by children playing: armed with opened mussels on a string, the children harvested 150 common shore crabs Carcinus maenas and a female Japanese shore crab ^[5].

Spreading in Belgium

Some studies claim that this crab was first introduced along the Belgian and Dutch coasts ^{[6, 7]}. After the first observation on Belgian territory (in 2006), it was predicted that the Japanese shore crab would be widely observed on the Belgian coast in the following years ^[5]. One month later, this was confirmed when the species was collected in Nieuwpoort, both under the rocks of a breakwater and on the western pier ^[8]. In 2008, the Japanese shore crab was found in abundance along the entire coastline: the species is mainly found in and around harbours – such as in Nieuwpoort and Ostend – but was also observed in the Sluice Dock of Ostend. Furthermore, the species has been observed on the beaches of Koksijde and Raversijde, and along the banks of the Scheldt ^[9].

Today, the Japanese shore crab can be found around offshore (deep sea) windmill constructions in the Belgian part of the North Sea. Unlike some other non-native species, which quickly found their way into wind farms, the Japanese shore crab took three to four years before it was found on these constructions. For the time being, the shore crab is only found on gravity-based foundations (GBFs), as this type of foundation best approximates the rocky formations on which the species normally thrives ^[10]. Furthermore, this shore crab has become very common on the Belgian breakwaters, where it is now more abundant than the common shore crab Carcinus maenas ^[11].

Spreading in neighbouring countries

The Japanese shore crab was found in Europe at about the same time in France and the Netherlands. The first sighting (two male crabs) was on the 21^st of August 1999 in the Dutch Eastern Scheldt. Eight days later, shore crabs were first spotted in Le Havre, in France. Here, the population was already so large that it was suspected that the Japanese shore crab had been present at least since 1998 ^[12]. In the Netherlands, it took until April 2003 before new individuals were spotted on the pier at Hook of Holland (a town located at the mouth of the river Maas, near The Hague) ^[13]. Since 2004, this exotic species has been observed regularly in the Delta region, especially in the Eastern- and Western Scheldt ^{[4, 13, 14]}.

In 2007, the Japanese shore crab extended its range further north into the southwest of the German Wadden Sea ^{[3, 7]}. By 2008, this crab had spread across most of the French side of the English Channel ^[6]. In the North Sea, given the relatively warm European climate, the crab could spread further north to 60°N ^[3]. In 2014 the species was also observed off the south coast of England ^[15].

Furthermore, the Japanese shore crab has been introduced into the Mediterranean Sea, more specifically along the coast of the Adriatic, since August 2001 ^[16]. As this is the only sighting so far, the species does not seem to have established itself here permanently ^[6]. Nevertheless, there are no climatic or physiological barriers to its southward migration. The crab could therefore spread to the Mediterranean Sea and the west coast of North Africa. In 2008, this species was spotted for the first time in the Black Sea ^[17]. The Japanese shore crab may never be able to establish itself here, as unfavourable conditions prevent the further development of the larvae ^[17]

It remains uncertain how this species was introduced into Europe. As with many species, it might have reached our shores in multiple ways. It was probably introduced via the ballast water of ships ^[3]. It is also possible that juvenile crabs – hiding in the fouling layer on the hulls of transport ships – were the first individuals of this species to arrive in Europe and establish new populations. It is also suspected that larvae or juvenile crabs hide among the shells during the transport of oyster spat from Japan. The transportation of ships may explain the first sightings near major international ports, while oyster import may explain the introductions near oyster farms ^{[10, 16]}. Nor can one rule out the possibility that the species got introduced independently, using different transport vectors. This was the case, for example, off the west coast of the United States, where multiple introductions were demonstrated ^[18].

However, a natural introduction via the Atlantic Ocean from the United States is impossible. Under optimal conditions, the free-living larvae need about 30 days to develop into crabs, and this development period is simply too short to cross the Atlantic by sea currents ^[16].

Within Europe, however, the species may naturally spread from already established populations (e.g. in France) to surrounding areas in both north- and southward directions. This is perhaps the case for the Belgian situation, where introductions from France and the Eastern or Western Scheldt are possible ^{[5, 12]}

The Japanese shore crab is mainly found between rocks, on groynes and piers. The large number of groynes and piers on the Belgian coast further enhance the local distribution ^{[5, 19]}.

The Japanese shore crab lives in the intertidal zone, i.e. the zone between low and high tide lines. Occasionally, individuals are found in open water, but always close to the coast. The species also occupies the zone above the high-water line (the spray zone or the supralittoral zone) ^{[2, 20]}. This spray zone is only flooded during spring tides and storms. It is a dangerous area, at least from a marine crab's point of view: predators are present and large fluctuations in temperature, salinity and humidity might occur. No native crabs live in this area; thus, the Japanese shore crab has no competition here ^{[10, 20]}. Crabs usually do not penetrate deep into estuaries ^[3]. Furthermore, Hemigrapsus sanguineus has few requirements regarding its habitat and can easily adapt to temperature fluctuations.

Observations show that this crab is a generalist predator ^[3]. The Japanese shore crab mainly feeds on plant material, but also consumes barnacles, amphipods, isopods, bristle worms and mussels. ^{[2, 20]}. The species also hunts on other, smaller crabs ^[3]. Shore crabs that have just caught some prey are often attacked by the Japanese shore crab. They do not attack with their claws but repel them with some leg punches ^[21].

Not only the lack of competition but also the fact that there are no parasites in Europe that can infect the Japanese shore crab plays to its advantage ^[22]. This is in contrast to the common shore crab, which is plagued by a parasite known as the Sacculina carcini ^{[2, 5]}. Crabs infected by this parasite can no longer moult or reproduce.

From established European populations, secondary dispersal is facilitated by natural processes (larvae hitching a ride on the sea currents) and shipping between European ports ^{[5, 12]}.

The Japanese shore crab produces up to 40,000 eggs at a time and can produce up to three broods per breeding season, which contributes to the rapid spread of the species. Temperature is an important factor for this crab: in cold water, the breeding season is shorter, and there are fewer successive broods, while their development is also much slower. The salinity of the seawater also plays an important role in the development of the Japanese shore crab. A salinity of less than 25 PSU prevents the metamorphosis of the last larval stage into an adult crab ^[20], although adult crabs can tolerate salt levels down to 10 PSU ^[12]. By way of comparison, the seawater in the North Sea has an average salinity of 35 PSU

The nutritional and environmental requirements of the Japanese shore crab overlap to a large extent with those of juvenile common shore crabs Carcinus maenas. Japanese shore crabs do not hesitate to attack and prey on these juvenile common shore crabs.

The Japanese shore crab can compete with the – also non-native – brush-clawed shore crab Hemigrapsus takanoi. The latter is smaller and needs more shelter, making it the less efficient competitor ^{[2, 4]}. However, the brush-clawed shore crab will not disappear altogether, as it thrives better than the Japanese shore crab in the more sheltered, silty regions ^[23].

It is also suggested that Hemigrapsus sanguineus may affect commercial species such as mussels, oysters, sand gapers and algae through excessive consumption of these species. ^{[22, 24]}.

In the United States, the Japanese shore crab appears to inhabit an empty niche. In the locations where it is most abundant, it does not appear to have a negative impact on the native crab populations. On the contrary, large numbers of Japanese shore crabs go hand in hand with a high species richness ^[25].

So far, there are no known measures to control the invasion of the Japanese shore crab, either in North America or in Europe. This might be because the species is already too widespread for measures to be effective ^[11]

The Japanese shore crab has an almost square carapace with a red to dark brown colour and lighter greenish spots. The side edges of the carapace have three teeth. The claws have purple-red spots, while the other legs have alternating light and dark bands. The males have a small bulb-like structure between the fingers of their claws, which gave them their name. The females have no such structures.

Males grow to an average width of 4.3 cm, while females can grow up to 4 cm. The maximum width of the dorsal shield is 5 cm ^[5].

The Japanese shore crab closely resembles the brush-clawed shore crab Hemigrapsus takanoi, and these two species can easily be confused. The brush-clawed shore crab has a more solid colour pattern and is rather brownish-green, although juveniles may have white spots. The two species can be distinguished by their size. With an average carapace width of 3.5 cm for males, the brush-clawed shore crab is smaller than the Japanese shore crab. Furthermore, the brush-clawed shore crab has no red spots on the top of its claws and the males have a tuft of yellow bristles where the Japanese shore crab has the bulb-like structure ^{[2, 5]}.

[1]          World Register of Marine Species (WoRMS) (2020). Hemigrapsus sanguineus (De Haan, 1835). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=158417] (2020-11-17).

[2]          d'Udekem d'Acoz, C.; Faasse, M. (2002). De huidige status van Hemigrapsus sanguineus (De Haan, 1835) en H. penicillatus (De Haan, 1835) in de noordelijke Atlantische Oceaan, in het bijzonder in Nederland, met opmerkingen over hun biologie (Crustacea, Decapoda, Brachyura). Het Zeepaard 62(4): 101-115. [http://www.vliz.be/en/imis?module=ref&refid=26193]

[3]          Epifanio, C.E. (2013). Invasion Biology of the Asian Shore Crab Hemigrapsus Sanguineus: A Review. J. Exp. Mar. Biol. Ecol. 441: 33-49. [http://www.vliz.be/en/imis?module=ref&refid=287904]

[4]          Faasse, M. (2004). Opmars van de Blaasjeskrab (Hemigrapsus sanguineus De Haan, 1835) in Nederland. Het Zeepaard 64(5): 143-144. [http://www.vliz.be/en/imis?module=ref&refid=67531]

[5]          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. [http://www.vliz.be/en/imis?module=ref&refid=105154]

[6]          Dauvin, J.-C.; Tous Rius, A.; Ruellet, T. (2009). Recent expansion of two invasive crabs species Hemigrapsus sanguineus (de Haan, 1835) and H. takanoi Asakura and Watanabe 2005 along the Opal Coast, France. Aquat. Invasions 4(3): 120-465. [http://www.vliz.be/en/imis?module=ref&refid=206505]

[7]          Obert, B.; Herlyn, M.; Grotjahn, M. (2007). First records of two crabs from the North West Pacific Hemigrapsus sanguineus and H. takanoi at the coast of Lower Saxony, Germany. WSN 33(1): 21-22. [www.vliz.be/en/imis?module=ref&refid=206451]

[8]          Nuyttens, F.; Versele, G.; Loones, M.-A. (2006). De aanwezigheid van de Penseelkrab Hemigrapsus takanoi en de Blaasjeskrab Hemigrapsus sanguineus in Nieuwpoort-Bad. De Strandvlo 26(3): 113-115. [www.vliz.be/en/imis?module=ref&refid=105162]

[9]          Kerckhof, F. (2019). Persoonlijke mededeling

[10]        Degraer, S.; Brabant, R.; Rumes, B. (Ed.) (2013). Environmental impacts of offshore wind farms in the Belgian part of the North Sea: Learning from the past to optimize future monitoring programmes. Royal Belgian Institute of Natural Sciences (RBINS), Operational Directorate Natural Environment, Marine Ecology and Management Section: Brussels. ISBN 978-90-9027-928-2. 239 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=231864]

[11]        d'Udekem d'Acoz, C. (2020). Persoonlijke mededeling

[12]        Breton, G.; Faasse, M.; Noel, P.; Vincent, T. (2002). A new alien crab in Europe: Hemigrapsus sanguineus (Decapoda: Brachyura: Grapsidae). J. Crust. Biol. 22(1): 184-189. [http://www.vliz.be/en/imis?module=ref&refid=25289]

[13]        Campbell, S.; Nijland, R. (2004). De Blaasjeskrab, Hemigrapsus sanguineus (De Haan, 1835), voor het eerst op het Nederlandse strand. Het Zeepaard 65(5): 151-152. [www.vliz.be/en/imis?module=ref&refid=76919]

[14]        Nijland, R.; Faasse, M. (2005). Meer vindplaatsen van Blaasjeskrab Hemigrapsus sanguineus (De Haan, 1835) in Nederland. Het Zeepaard 65(5): 151-152. [http://www.vliz.be/en/imis?module=ref&refid=76919]

[15]        Seeley, B.; Sewell, J.; Clark, P.F. (2015). First GB records of the invasive Asian shore crab, Hemigrapsus sanguineus from Glamorgan, Wales and Kent, England. Marine Biodiversity Records 8(e102): 1-4. [http://www.vliz.be/nl/catalogus?module=ref&refid=312321]

[16]        Schubert, C.D. (2003). The east Asian shore crab Hemigrapsus sanguineus (Brachyura: Varunidae) in the Mediterranean Sea: an independent human-mediated introduction. Sci. Mar. (Barc.) 67(2): 195-200. [http://www.vliz.be/en/imis?module=ref&refid=38548]

[17]        Micu, D.; Niţă, V.; Todorova, V. (2010). First record of the Japanese shore crab Hemigrapsus sanguineus (de Haan, 1835)(Brachyura: Grapsoidea: Varunidae) from the Black Sea. Aquat. Invasions 5. [http://www.vliz.be/nl/catalogus?module=ref&refid=297360]

[18]        Blakeslee, A.M.H.; Kamakura, Y.; Onufrey, J.; Makino, W.; Urabe, J.; Park, S.; Keogh, C.L.; Miller, A.W.; Minton, M.S.; Carlton, J.T.; Miura, O. (2017). Reconstructing the Invasion History of the Asian shorecrab, Hemigrapsus sanguineus (De Haan 1835) in the Western Atlantic. Mar. Biol. (Berl.) 164(3): 47. [http://www.vliz.be/nl/catalogus?module=ref&refid=300145]

[19]        Lohrer, A.M.; Fukui, Y.; Wada, K.; Whitlatch, R.B. (2000). Structural complexity and vertical zonation of intertidal crabs, with focus on habitat requirements of the invasive Asian shore crab, Hemigrapsus sanguineus (de Haan). J. Exp. Mar. Biol. Ecol. 244: 203-217. [http://www.vliz.be/en/imis?module=ref&refid=39836]

[20]        McDermott, J.J. (2000). Natural history and biology of the Asian Shore Crab Hemigrapsus sanguineus in the Western Atlantic: a review, with new information, in: Pederson, J. Marine bioinvasions: Proceedings of a conference January 24-27, 1999. MIT Sea Grant College Program, 00(2). pp. 193-199. [http://www.vliz.be/en/imis?module=ref&refid=66936]

[21]        Jensen, G.C.; McDonald, P.S.; Armstrong, D.A. (2002). East meets west: competitive interactions between green crab Carcinus maenas, and native and introduced shore crab Hemigrapsus spp. Mar. Ecol. Prog. Ser. 225: 251-262. [http://www.vliz.be/en/imis?module=ref&refid=36393]

[22]        Global Invasive Species Database (2018). Hemigrapsus sanguineus. [http://www.iucngisd.org/gisd/species.php?sc=756] (2018-08-08).

[23]        Faasse, M. (2019). Persoonlijke mededeling

[24]        Tyrrell, M.C.; Harris, L.G. (2000). Potential impact of the introduced Asian Shore Crab, Hemigrapsus sanguineus, in northern New England: diet, feeding preferences and overlap with the Green crab, Carcinus maenas., in: Pederson, J. Marine bioinvasions: Proceedings of a conference January 24-27, 1999. MIT Sea Grant College Program, 00(2). pp. 208-220. [http://www.vliz.be/en/imis?module=ref&refid=66942]

[25]        Altieri, A.H.; Van Wesenbeeck, B.K.; Bertness, M.D.; Silliman, B.R. (2010). Facilitation cascade drives positive relationship between native biodiversity and invasion success. Ecology 91(5): 1269-1275. [http://www.vliz.be/en/imis?module=ref&refid=206504]

VLIZ Alien Species Consortium (2020). Hemigrapsus sanguineus – Japanese shore crab. Non-native species of the Belgian part of the North Sea and bordering estuaries anno 2020. Flemish Institute for the Sea (VLIZ). 8 pp.