Taxonomic name: Rhithropanopeus harrisii (Gould, 1841)
Synonyms: Heteropanope tridentata De Man J. G. (1892), Pilumnus harrisii (Gould, 1841), Pilumnus tridentatus (Maitland, 1874), Rhithropanopeus harrisii ssp. tridentatus (Buitendijk and Holtuis 1949)
Common names: Brackwasserkrabbe (German), estuarine mud crab (English), Golandsky crab (Russian), Harris mud crab (English), krabik amerykanski (Polish), Østamerikansk brakvandskrabbe (Danish), white-fingered mud crab (English), Zuiderzee crab (English), Zuiderzeekrabbe (German), Zuiderzeekrabbetje (Dutch)
Organism type: crustacean
Rhithropanopeus harrisii is a small estuarine crab native to the Atlantic Coast of North America. It has invaded many locations in Europe and North America and is presumed to have dispersed mainly via oyster translocations and shipping. Anecdotal reports indicate that it can alter food webs, compete with native species, foul pipe systems, and be a vector of the white spot baculovirus.
Rhithropanopeus harrisii, or the Harris mud crab, is a small euryhaline crab. It reaches approximately 2cm in carapace width as an adult and is greenish-brown or olive in colouration. It has white-tipped claws, unequal in size and dissimilar. The front of its carapace is almost straight, slightly notched, with its margin transversely grooved, appearing double when viewed from the front. Four anterolateral teeth (spines) line the side of its carapace between the eyestalks and the widest portion of the carapace. Its four walking legs are long, slender and sparsely hairy. (Williams 1984; Perry, 2007).
estuarine habitats, lakes
Rhithropanopeus harrisii can be found in estuaries and quasi-freshwater lakes with salinities as low as 0.4 ppt (Keith, 2006). It prefers brackish waters and commonly inhabits shores with muddy or sandy substrates. It usually associates with structures providing shelter such as oyster reefs, vegetation, logs, or debris of some type. It is tolerant to a wide range of salinities rendering it capable of invading a variety of aquatic habitats (Williams 1984, Petersen, 2006, Roche and Torchin 2007).
No study has yet quantified the impacts of Rhithropanopeus harrisii, but anecdotal reports in the scientific literature indicate that it can alter food webs, compete with and potentially displace native crabs, crayfish, as well as benthophagous fishes (reviewed in Roche and Torchin 2007). In the Caspian Sea, where it has reached very high densities, the crab is responsible for fouling water intake pipes and causes economic loss to fishermen by spoiling fishes in gill nets (Zaitsev and Öztürk 2001). In Texas, the crab has become very abundant in almost freshwater reservoirs and is reported to foul PVC intakes in lakeside homes and clog the cooling system of a nuclear powerplant in Glenrose (Keith, 2006; Hildebrand, pers. comm..). Payen and Bonami (1979) also identified R. harrisii as a carrier of the white spot baculovirus, which causes disease in penaeid prawn species and the blue crab (Callinectes sapidus).
Rhithropanopeus harrisii has been used as a study organism in many developmental and physiological studies (e.g. Christiansen and Costlow, 1975; Kalber and Costlow, 1966). The crab has also been used to examine the effects of various pesticides on non-target crustacean species (Clare et al. 1992), including juvenile hormone analogues (JHA's), a pest control agent which mimics insect larval hormones (Cripe et al. 2003).
In Europe, Maitland (1874) initially described Rhithropanopeus harrisii as a native species, Pilumnus tridentatus. In 1949, Buitendijk and Holthuis recognized the exotic origins of this crab and reclassified it as Rhithropanopeus harrisii ssp. tridentatus, a synonym which has often been used to designate this species in Europe (Christiansen, 1969; Wolff, 2005).
Native range: North and Central American Atlantic Coast from the Gulf of the St. Lawrence River, Canada, to Vera Cruz, in the Gulf of Mexico (Williams, 1984). Williams (1984) corrected his erroneous listing of Brazil as part of R. harrisii native range (Williams, 1965 in Roche & Torchin 2007).
Known introduced range: Adriatic Sea, Aral Sea, Azerbaijan, Azov Sea, Baltic Sea, Belgium, Black Sea, Britain, Bulgaria, Caspian Sea, Denmark, France, Germany, Iran, Italy, Kazakhstan. Lithuania, Mediterranean Sea, Netherlands, North Sea, Panama Canal, Poland, Portugal, Romania, Russia, Spain, Tunisia, Turkmenistan, Ukraine, Uzbekistan, Pacific Coast and Texas lakes of United States.
Introduction pathways to new locations
Other: Although not confirmed, Rhithropanopeus harrisii is thought to have been introduced accidentally along with Atlantic oysters Crassostrea virginica to the San Francisco Bay (Roche, 2007).
Ship ballast water: Although only confirmed on a few occasions, transport of decapods in ships' ballast water is considered the most common and effective means of introduction of exotic decapods including Rhithropanopeus harrisii (Rodriguez, 2001).
Ship/boat hull fouling: Rhithropanopeus harrisii are known to have dispersed by attaching to the hulls of ships. This however has declined since the advent of metallic hulls and antifouling paints (Rodriguez, 2001).
Local dispersal methods
Natural dispersal (local):
Preventative measures: Transport in ballast water is thought to be the main vector of introduction for Rhithropanopeus harrisii. The GloBallast Programme has been established to reduce introductions of non-native species (such as R. harrisii) by providing funding and assistance to less-industrialized countries in order to reduce the transfer of harmful aquatic organisms and pathogens in the ballast water of ships. Implemented by the International Maritime Organization (IMO) with funding by the Global Environment Facility (GEF) and the United Nations Development Program (UNDP), this programme will facilitate the implementation of the newly adopted IMO Ballast Water Convention in developing countries (GloBallast, undated).
Chemical: Diflubezuron, the active chemical in the pesticide Dimilin, has been experimentally used on R. harrisii (see McEnnulty et al., 2001). It is lethal to hatching larvae in concentrations of 7-10ppb. It works by inhibiting chitin synthesis and has been found to be an effective way of controlling arthropods. However, it lacks specificity and may take several weeks to degrade in brackish water environments (Christiansen and Costlow 1980).
Biological: The rhizocephalan barnacle Loxothylacus panopaei parasitizes R. harrisii in its native range. Parasitic barnacles infect their crab hosts at the larval stage (cyprid or cypris larva), develop as an endoparasite, and then produce an external reproductive body called the externa. Rhizocephalans stunt growth in their hosts and cause castration in both males and females, preventing future reproduction. Alvarez et al. (1995) experimentally infected R. harrisii from the Chesapeake Bay with L. panopaei and found that parasitism had a significant effect on the survival of infected hosts. However, further studies are necessary to determine whether L. panopei is a viable candidate for biological control of R. harrisii in its introduced range.
Rhithropanopeus harrisii is omnivorous and known to feed on mangrove and leaf detritus, bivalve molluscs, oligochaetes, and dead fish. Small crabs have been observed to feed on small crustaceans such as amphipods and copepods. (Williams, 1984; Karpinsky, 2005).
Oviparous. Sexual. Males place spermatophores into the female’s sprematheca. Unlike most other crab species, Rhithropanopeus harrisii females do not moult immediately before copulation, which usually takes place during the summer months. Approximately three to four days after copulation, females bury themselves up to the eye stalks to lay their eggs. This behaviour facilitates the attachment of the eggs to the pleopods. Ovigerous females will then remain sheltered in debris, shells, or sediment. Females usually lay between 1200 and 4800 eggs at a time depending on their size. In the Kiel Canal, Germany, large females were observed to lay as many as 16,000 eggs (Turoboyski, 1973).
Eggs remain attached to the mother’s pleopods until they hatch. Ovigerous females exhibit a rhythmic pumping behaviour when hatching begins, which helps synchronize hatching and facilitates larval release (Forward and Lohmann, 1983). Rhithropanopeus harrisii develops in four zoeal larval stages and a megalopal post larval stage before reaching adulthood. Development averages 16 days (Cripe et al., 2003). Sexual maturity can be reached as early as the breeding season following birth, at a carapace width of 4.5mm for males and 4.4 to 5.5mm for females (Ryan, 1956; Turoboyski, 1973).
Reviewed by: Dominique Roche MacGill University Canada
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Friday, 11 January 2008