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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Harris mud crab

Synonyms and Other Names: Pilumnus harrisii Gould, 1841; white-fingered mud crab

Taxonomy: available through www.itis.gov

Identification: Front of body is almost straight, slightly notched; frontal margin transversely grooved, appearing double when viewed from front. First two antero-lateral teeth fused, last three dentiform. Chelipeds (structure supporting the chela) unequal and dissimilar; major chela (claws) with short fixed finger and strongly curved dactyl; minor chela with longer fixed finger and relatively straight dactyl (walking leg); dactyls light in color; chelipeds nearly smooth in old individuals; carpus of chelae in juveniles rough with lines and granules. Walking legs are long, slender and somewhat hairy. Color brown to olive green (Rathbun 1930; Williams 1984).

Size: Williams (1984) reported males with a carapace width of 21.3 mm.

Native Range: Original range presumed to be in fresh to estuarine waters from the southwestern Gulf of St. Lawrence, Canada, through the Gulf of America to Vera Cruz, Mexico (Williams 1984).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Rhithropanopeus harrisii inhabits areas with no current (Texan reservoirs) as well as areas with current (Eider, Elbe, Ems, and Weser Rivers) (Jensen 2010).  In Texas reservoirs, habitat includes sand and gravel mixed with a few stones for cover (Richey 2004). In the Baltic Sea, it can opportunistically occupy extremely diverse habitats, such as shafts of dead marsh plants, self-made burrows in muddy bottoms, under small stones along the shore, and the brown algae Fucus vesiculosus in hard bottoms sometimes exposed to heavy wind and waves, up to 37 m depth (Fowler et al. 2013).  It is found in eutrophic waters in its native habitat in the Gulf of America, and in mesotrophic waters in its invaded range in the Baltic Sea (Glasby and Szefer 1998). Rhithropanopeus harrisii lives in a pH range of 5.4-7.8 (Roche et al. 2009).

While much of the previous literature describes this species as intolerant of freshwater conditions, populations have recently been found in near-freshwater conditions. Roback (1955) found this species in rivers emptying into the Gulf of America in salinities from 0.006 to 22.6 ppt (Costlow et al. 1966). However, zoeae (larvae) develop in salinities up to 40 ppt (Costlow et al. 1966). Rhithropanopeus harrisii populations have been found well-established (metamorphosis and reproduction) in Tradinghouse Creek reservoir (Texas), which has a salinity of 0.4–0.5 ppt (Boyle et al. 2010). High percentage of eggs from these Texan reservoirs hatched in the lab at salinity of 0.5 ppt (Richey 2004). Rhithropanopeus harrisii is well established and successfully reproducing in the Northern Lagoon (Panama), with constantly recorded salinities between 0.4 ppt and 0.6 ppt (Roche et al. 2009). Reasons for freshwater tolerance (where none had been found before) could be because the source population is more tolerant to low salinity (Boyle et al., 2010). Texas populations may be from Florida and/or Gulf of America populations, which show greater tolerance to low salinity (Richey 2004).  Louisiana populations are genetically distinct from American East Coast and Europe populations (Projecto-Garcia et al. 2010). Freshwater tolerance could also be a recent result of natural selection, based on the ability of a small number of individuals. 

Turoboyski (1973) reported that populations in the Vistula River, Poland could survive winter temperatures below 1°C and could even survive being frozen in ice for a short time. This is not particularly unusual as populations at the northern edge of their natural range in the Miramichi Estuary, Canada are exposed to salt water near freezing for up to six months of the year (Chadwick 1995; Fowler et al. 2013).  Rhithropanopeus harrisii has been recorded in water with dissolved oxygen concentrations of 0.554 mg/L (Turoboyski 1973).

In its introduced range in Poland, R. harrisii is able to reproduce when the water temperature is above 14°C (Turoboyski 1973); zoeae develop at temperatures below 30°C (Costlow et al. 1966).  Since zoeae are retained in estuaries, they develop in a highly variable environment. Accordingly, they can complete development in a very wide range of temperatures and salinities (Forward 2009). Reid et al. (2007) and Klein et al. (2010) measured rapid declines in dissolved oxygen concentration inside ballast tanks to 2 mg/L within 5 to 7 days, with 90% of initial oxygen content lost within 10 days at temperatures above 20°C.  This species inhabits polluted areas, including the Baltic Sea, which is heavily polluted (though improvements have been made) (Glasby and Szefer 1998).

Rhithropanopeus harrisii feeds on both plants and animals, the proportions between these two major components differing between areas (Kujawa 1957; Turoboyski 1973) and often shifting towards more animal prey as size increases (Aarnio et al. 2015; Zalota et al. 2017). The type of food consumed has been found to be significantly (P<0.05) dependent on the locality inhabited: the greater the biodiversity of the habitat, the richer the dietary consumption. For example, while Rhithropanopeus harrisii dwelling in the Vistula Lagoon fed mainly on Dreissena polymorpha (Pallas, 1771) (cf. Kujawa 1957), the major food items in the Dead Vistula included Nereis diversicolor (0. F. Muller, 1776) Mytilus edulis (Linnaeus, 1758), D. polymorpha, and Cordylophora caspia (Pallas, 1771), as well as the algae Cladophora sp. and Enteromorpha sp. (cf. Turoboyski 1973). An Odra estuary population was found to feed mainly on detritus, which accounted for 61.1% of the gut content; the animal food items, making up 12.9% of the contents, contained remains of appendages of copepods and insects, as well as fragments of the blue mussel (M. edulis) and the zebra mussel (D. polymorpha) (Czerniejewski and Rybczyk 2008). In Baltic coastal waters this species feeds on detritus, and also on animal and plant matter. Remains of Chlorophyta, Amphipoda, Ostracoda, Polychaeta, Gastropoda and Bivalvia were found in the stomachs of the specimens analyzed (Hegele-Drywa and Normant 2009).

Rhithropanopeus harrisii can become a dominant benthic species in areas where it has been introduced.  It is one of the most important benthic species in the Vistula lagoon (Baltic sea), where it is non-native. It contributes heavily to the productivity, matter transformation, and habitat modification of the lagoon (Ezhova et al. 2005).  Rhithropanopeus harrisii appears to occupy the same niche as crayfish, which means crayfish could easily be displaced if Rhithropanopeus harrisii is the better competitor. Observations over three summers at Possum Kingdom State Park in Texas have indicated an abundance of crabs and a paucity of crayfish (Richey 2004).

Rhithropanopeus harrisii typically produces 1000 to 4000 eggs, and up to 7500 eggs per clutch (Morgan et al. 1983). Female R. harrisii individuals are able to release fertilized egg clutches up to four separate times following a single mating. Multiple spawnings may also assure continued reproduction under stressful or hazardous conditions, when mating activity may be reduced (Morgan et al. 1983). Rhithropanopeus harrisii zoeae can detect and move in response to vertical gradients in temperature, salinity, and hydrostatic pressure, which allows for depth regulation and avoidance of adverse environmental conditions (Forward 2009).  After R. harrisii megalopae (first stage of crab morphology) settle out in a suitable habitat, they quickly grow to reproductive size. Rhithropanopeus harrisii is physiologically able to reproduce by the fifth crab stage (Payen 1975), which takes only a month to attain after metamorphosis at 25°C (Morgan et al. 1983).

Means of Introduction: Christiansen (1969) noted that the spread of this crab was probably associated with shipping, possibly in ballast or clinging to the hulls of ships. Spread of the mud crab from California to Oregon occurred via currents during the larval stage (Petersen 2002). Howells (2001) noted that the source of introductions to Texas reservoirs may have resulted from "bait bucket or accidental angler/boater releases" or fish stocking activities from a coastal hatchery where R. harrisii occurs naturally.

Status: Established in most areas of occurrence.

Impact of Introduction: Payen and Bonami (1979) noted that this species is a carrier of strains of the white spot baculovirus. These viruses are extremely virulent and cause disease in penaeid shrimp and the blue crab. In Texas, the crabs have caused fouling problems in PVC intakes to lakeshore homes and there is evidence that they have disrupted natural community structure by replacing the crayfish that are native to local lakes.

References: (click for full references)

Aladin, N. V., and W. T. W. Potts. 1992. Changes in the Aral Sea ecosystems during the period 1960–1990. Hydrobiologia 237:67-79.

Bacevicius, E., and Z.R. Gasiunaite. 2008. Two crab species- Chinese mitten crab (Eriocheir sinensis Edw.) and mud crab (Rhithropanopeus harrisii (Gould) ssp. tridentatus (Maitland) in the Lithuanian coastal waters, Baltic Sea. Transitional Waters Bulletin 2: 63-68.

Boyle, J. T., D. Keith, and R. Pfau. 2010. Occurrence, reproduction, and population genetics of the Estuarine Mud Crab, Rhithropanopeus harrisii (Gould) (Decapoda, Panopidae) in Texas freshwater reservoirs. Crustaceana 83:493-505.

Briski, E., S. Ghabooli, S. A. Bailey, and H. J. MacIsaac. 2012. Invasion risk posed by macroinvertebrates transported in ships’ ballast tanks. Biological invasions 14:1843-1850.

Chadwick, M. 1995. Water, science, and the public: the Miramichi Ecosystem. Canadian Special Publication of Fisheries and Aquatic Sciences 123: 1-300.

Costlow, J. D., C. G. Bookhout, and R. J. Monroe. 1966. Studies on the larval development of the crab, Rhithropanopeus harrisii (Gould). I. The effect of salinity and temperature on larval development. Physiological Zoology 39:81-100. https://doi.org/10.1086/physzool.39.2.30152421

Czerniejewski, P., and A. Rybczyk. 2008. Body weight, morphometry, and diet of the mud crab, Rhithropanopeus harrisii tridentatus (Maitland, 1874) in the Odra estuary, Poland. Crustaceana 81:1289-1299.

Ezhova, E., L. Zmudzinski, and K. Maciejewska. 2005. Long-term trends in the macrozoobenthos of the Vistula Lagoon, southeastern Baltic Sea. Species composition and biomass distribution. Bulletin of the Sea Fisheries Institute 1:55-73.

Forward, R. B. 2009. Larval biology of the crab Rhithropanopeus harrisii (Gould): a synthesis. The Biological Bulletin (Lancaster) 216:243-256.

Fowler, A., T. Forsstrom, M. von Numers, and O. Vesakoski. 2013. The North American mud crab Rhithropanopeus harrisii (Gould, 1841) in newly colonized Northern Baltic Sea: distribution and ecology. Aquatic Invasions 8:89-96.

Glasby, G. P., and P. Szefer. 1998. Marine pollution in Gdansk Bay, Puck Bay and the Vistula Lagoon, Poland: An overview. Science of The Total Environment 212:49-57.

Goncalves, F., R. Ribeiro, and A.V.M. Soares. 1995. Rhithropanopeus harrisii, an American crab in the estuary of the Modego River, Portugal. Journal of Crustacean Biology 15(4): 756-762.

Gosner, K.L. 1979. A field guide to the Atlantic seashore. Houghton Mifflin. Boston, Massachusetts.

Goulletquer, P., G. Bachelet, P.G. Sauriau, and P. Noel. 2002. Open Atlantic coast of Europe- A century of introduced species into French waters. Pages 276-290. in Leppakoski, E., S. Gollasch, and S. Olenin (eds.). Invasive aquatic species of Europe. Distribution, impacts, and management.

Grabowski, M., K. Jazdzewski, and A. Konopacka. 2005. Alien crustacea in Polish waters-- introduction and decapoda. Oceanological and Hydrobiological Studies 34:43-61.

Hegele-Drywa, J., and M. Normant. 2009. Feeding ecology of the American crab Rhithropanopeus harrisii (Crustacea, Decapoda) in the coastal waters of the Baltic Sea. Oceanologia 51:361-375.

Howells, R.G. 2001. Introduced non-native fishes and shellfishes in Texas waters: an updated list and discussion. Texas Parks and Wildlife Department, Inland Fisheries Division.

IUCN SSC Invasive Species Specialist Group. 2008. Rhithropanopeus harrisii. https://www.iucngisd.org/gisd/speciesname/Rhithropanopeus+harrisii

Jensen, K. R. 2010. NOBANIS – Invasive Alien Species Fact Sheet – Rhithropanopeus harrisii – From: Identification key to marine invasive species in Nordic waters – NOBANIS www.nobanis.org.

Klein, G., K. MacIntosh, I. Kaczmarska, and J.M. Ehrman. 2010. Diatom survivorship in ballast water during trans-Pacific crossings. Biological Invasions 12: 1031-1044.

Kujawa, S. 1957. Biology and cultivation of the crab R. harrisii tridentatus from the Vistula Lagoon, Wszechswiat 2: 57-59.

Kulp, R. E., V. Politano, H. A. Lane, S. A. Lombardi, and K. T. Paynter. 2011. Predation of juvenile Crassostrea virginica by two species of mud crabs found in the Chesapeake Bay. Journal of Shellfish Research 30:261-266.

Morgan, S. G., J. W. Goy, and J. D. Costlow, Jr. 1983. Multiple Ovipositions from Single Matings in the Mud Crab Rhithropanopeus harrisii. Journal of Crustacean Biology 3:542-547.

Nehring, S. 2000. Zur Bestandssituation von Rhithropanopeus harrisii (Gould, 1841) in deutschen Gewassern: die sukzessive Ausbreitun eines amerikanischen Neozoons (Crustacea: Decapoda: panopeidae). Senckenberg marit 30: 115-122.

Normant, M., J. Miernik, and A. Szaniawska. 2004. Remarks on the morphology and the life cycle of Rhithropanopeus harrisii ssp. tridentatus (Maitland) from the Dead Vistual River. Oceanological and Hydrobiological Studies 33(4): 93-102.

Olesen, A.J., and O.S. Tendal. 2009. Amerikansk brakvandskrabbe- ny krabbeart etableret i Danmark. Zoologisk Museum 2: 26-28.

Payen, G.G., and J.-R. Bonami. 1979. Mise en evidence de particules d'allure virale associees aux noyaux des cellules mesodermiques de la zone germinative testiculaire du crabe Rhithropanopeus harrisii (Gould) (Brachyoure, Xanthide). Rev Trav Inst Pech Marit 43: 361-365.

Projecto-Garcia, J., H. Cabral, and C. D. Schubart. 2010. High regional differentiation in a North American crab species throughout its native range and invaded European waters: a phylogeographic analysis. Biological invasions 12:253-263.

Rasmussen, E. 1958. Immigrants in the southern harbour of Copenhagen. naturens Verden 1958: 3-8.

Rathbun, M.J. 1930. The cancroid crabs of America of the families Euryalidae, Portunidae, Atelecyclidae, Cancridae, and Xanthidae. Smithsonian Institution, United States National Museum, Bulletin 152: 1-609.

Reid, D.F., T. Johengen, H.J. MacIsaac, F.C. Dobbs, M. Doblin, L. Drake, G.M. Ruiz, P.T. Jenkins, S. Santagata, C.D.A. van Overdijk, D. Gray, S. Ellis, Y. Hong, Y. Tang, F. Thomson, S. Heinemann, S. Rondon. 2007. A final report for the project "Identifying, verifying, and establishing options for best management practices for NOBOB vessels". National Oceanic and Atmospheric Administration, Great Lakes Environmental Research  Laboratory, and University of Michigan Cooperative Institute for Limnology and Ecosystems Research, Ann Arbor.

Reisser, C. E., and R. B. Forward. 1991. Effect of salinity on osmoregulation and survival of a rhizocephalan parasite, Loxothylacus panopaei, and its crab host, Rhithropanopeus harrisii. Estuaries 14:102-106.

Richey, H.M., IV. 2004. Reproduction of the exotic estuarine mud crab Rhithropanopeus harrisii in Texas impoundments. Unpublished M.S. thesis. Tarleton State University, Stephenville, Texas. https://www.proquest.com/docview/305055496?accountid=14667&parentSessionId=l4pKA7jMd6Q6C7HVNtU11rnatLxwVIsQrbRUZ6%2BHlZ8%3D

Roche, D. G., M. E. Torchin, B. Leung, and S. A. Binning. 2009. Localized invasion of the North American Harris mud crab, Rhithropanopeus harrisii, in the Panama Canal: implications for eradication and spread. Biological invasions 11:983-993.

Turoboyski, K. 1973. Biology and ecology of the crab Rhithropanopeus harrisii ssp. tridentatus. Marine Biology 23:303-313.

Williams, A. 1984. Shrimps, lobsters, and crabs of the Atlantic coast of the eastern United States, Maine to Florida. Smithsonian Institution Press, Washington, DC.

Wolff, W.J. 2005. Non-indigenous marine and estuarine species in the Netherlands. Zoologische Mededelingen Leiden 79: 1-116.

Zaitsev, Y., and B. Ozturk. 2001. Exotic species in the Aegean, Marmara, Black, Azov and Caspian Seas. Turkish Marine Research Foundation. Istanbul, Turkey. 265 pp.

Other Resources:
US Fish and Wildlife Service Ecological Risk Screening Summary for Rhithropanopeus harrisii

Author: Perry, H., Fusaro, A., Davidson, A., Alame, K., Gappy, M., Conard, W., Bartos, A.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.