Species Description: The Atlantic mud crab, Panopeus herbstii, is one of many species of mud crabs belonging to the family Xanthidae. Crabs included in Panopeus and related genera have five teeth lining the outside of the carapace on each side, the first two mostly fused (Gosner 1978).
The fingers, or top and bottom portions of the closable claw, are usually black to brown in most species; whereas, the interior portion at the base of the claw, called the palm, is usually pale. The claws are distinctly unequal in size, and the body is brownish. The carapace of P. herbstii is brownish green and slightly granular in texture, with sharp 2nd, 3rd, and 4th marginal teeth on either side (Kaplan 1988, Voss 1980). The appendages bearing the claws, called chelipeds, are darker and often spotted. Both fingers on each claw are black, and the color of the lower finger often extends up the palm. An enlarged, white tooth is present at the base of the upper finger on the larger claw (eg. Ruppert & Fox 1988). The 3rd maxilliped, or feeding appendage, is marked with a red spot in males, sometimes in females (Gosner 1978). All walking legs are hairy and slender (Voss 1980).
Regional Occurrence & Habitat Preference: The range of P. herbstii extends from Massachusetts to Brazil (Gosner 1978, Kaplan 1988). Most populations inhabit muddy bottoms, mainly in mangrove swamps and oyster beds (Kaplan 1988, Ruppert & Fox 1988, Voss 1980). However, both adults and juveniles can also be found on jetty rocks, shell or cobble bottoms, and marsh edges (Dittel et al. 1996). In oyster beds and under rocks, individuals may excavate shallow burrows to a depth of 4-10 cm (Williams 1984).
IRL Distribution: The Atlantic mud crab occurs throughout the IRL, mostly in muddy sediments of oyster beds and around mangrove roots. Individuals can also be found in rocky areas and around pilings.
Age, Size, Lifespan: The maximum age of P. herbstii is unknown, and the lifespan can vary with food availability and environmental factors. With the exception of the stone crab, Menippe mercenaria, the Atlantic mud crab is the largest xanthid species in the southeast United States (Ruppert & Fox 1988). The maximum reported carapace width for P. herbstii is 6.4 cm (Ruppert & Fox 1988), though most specimens are much smaller at widths of 3-4 cm (Gosner 1978, Kaplan 1988).
Abundance: Atlantic mud crabs can be found in aggregated, large populations to solitary individuals spread throughout an area. Densities for P. herbstii in salt marshes from Delaware to North Carolina ranged between 0 and 82 individuals per square meter, and were positively correlated with the height of the cordgrass, Spartina alterniflora, and the density of bivalve prey (Silliman et al. 2004).
Reproduction: As with most decapod crustaceans, fertilization occurs during copulation. The male transfers sperm-filled cases, called spermatophores, to the female. After the eggs are fertilized, the female broods them on her abdomen until hatching. Reproduction is seasonal in some locations, and is likely linked to water temperature and food availability. In Delaware Bay, P. herbstii spawns throughout the summer months (Rodriguez & Epifanio 2000).
Embryology / Larval Development: Like many other crabs, P. herbstii females carry large broods of eggs on their abdomen, often referred to as sponges. Once hatched, larvae pass through four zoeal stages and one megalopa before settling to the benthos and metamorphosing into juveniles (Williams 1984). Zoeae of mud crabs have characteristically large spines that have developed as protection against predatory fishes (Morgan 1989). After release, larvae are retained within estuarine waters during the entire planktonic period by undergoing vertical migration and utilizing inward-flowing bottom currents (eg. Dittel & Epifanio 1982).
Temperature: Little is known about the thermal tolerances of P. herbstii, but the temperate to tropical distribution of the species suggests that it can withstand a wide range of temperatures. Individuals have been kept in captivity at a water temperature range of 5 to 30°C (Dame & Vernberg 1978).
Salinity: The Atlantic mud crab is usually found throughout estuaries in brackish waters above 10 ppt (Gosner 1978, Rodriguez & Epifanio 2000).
Parasites: Several species of crustaceans are hosts to a variety of parasitic organisms. The Atlantic mud crab is parasitized by the isopod, Cancrion carolinus (Ruppert & Fox 1988). In addition, P. herbstii is a host to castrating rhizocephalan barnacles of the genus Loxothylacus (eg. Reinhard & Reischman 1958).
Associated Species: No known obligate associations exist for P. herbstii. However, Atlantic mud crabs are associated with several organisms common to rocky intertidal areas, mangroves and oyster beds.
Ecological Importance: As a top predator of the marsh periwinkle, Littorina irrorata, the Atlantic mud crab helps to keep snail populations in check that could otherwise decimate salt marsh vegetation (Silliman et al. 2004). For more information on this subject, visit the species report page for the marsh periwinkle.
Negative impacts of the Atlantic mud crab include those to the shellfish industry, stemming from the significant consumption of juvenile oysters and hard clams by P. herbstii (Castagna & Kraeuter 1977, Whetstone & Eversole 1981).
Andrews, WR, Targett, NM & CE Epifanio. 2001. Isolation and characterization of the metamorphic inducer of the common mud crab, Panopeus herbstii. J. Exp. Mar. Biol. Ecol. 261: 121-134.
Castagna, M & JN Kraeuter. 1977. Mercenaria culture using stone aggregate for predator protection. Proc. Natl. Shellfish Assoc. 67: 1-6.
Dame, RF & FJ Vernberg. 1978. The influence of constant and cyclic acclimation temperatures on the metabolic rates of Panopeus herbstii and Uca pugilator. Biol. Bull. 154: 188-197.
Dittel, AR & CE Epifanio. 1982. Seasonal abundance and vertical distribution of crab larvae in Delaware Bay. Estuaries. 5: 197-202.
Dittel, AR, Epifanio, CE & C Natunewicz. 1996. Predation on mud crab megalopae, Panopeus herbstii H. Milne Edwards: effect of habitat complexity, predator species and postlarval densities. J. Exp. Mar. Biol. Ecol. 198: 191-202.
Epifanio, CE, Lobanoff, ML, Connaughton, VP & J Welch. 1994. Growth and development of mud crab larvae in field-deployed enclosures and in the laboratory. J. Exp. Mar. Biol. Ecol. 180: 165-174.
Gosner, KL. 1978. A field guide to the Atlantic seashore: Invertebrates and seaweeds of the Atlantic coast from the Bay of Fundy to Cape Hatteras. Houghton Mifflin Co. Boston, MA. USA. 329 pp.
Grabowski, JH. 2004. Habitat complexity disrupts predator-prey interactions but not the trophic cascade on oyster reefs. Ecology. 85: 995-1004.
Harvey, EA & CE Epifanio. 1997. Prey selection by larvae of the common mud crab Panopeus herbstii Milne-Edwards. J. Exp. Mar. Biol. Ecol. 217: 79-91.
Kaplan, EH. 1988. A field guide to southeastern and Caribbean seashores: Cape Hatteras to the Gulf coast, Florida, and the Caribbean. Houghton Mifflin Co. Boston, MA. USA. 425 pp.
Maurer, D & L Watling. 1973. Studies on the oyster community in Delaware: the effects of the estuarine environment on the associated fauna. Int. Rev. Gesamten Hydrobiol. 58: 161-201.
McDermott, JJ. 1960. The predation of oysters and barnacles by crabs of the family Xanthidae. Proc. Pennsylvania Acad. Sci. 34: 199-211.
McDermott, JJ & FB Flower. 1952. Preliminary studies of the common mud crabs on oyster beds of Delaware Bay. Conv. Adr. Natn. Shellfish Assoc. 1952: 47-50.
McDonald, J. 1977. The comparative intertidal ecology and niche relations of the sympatric mud crabs, Panopeus herbstii (Milne-Edwards) and Eurypanopeus depressus (Smith), at North Inlet, South Carolina, USA (Decapoda: Brachyura: Xanthidae). PhD Dissertation. University of South Carolina. Columbia, SC. USA.
Morgan, SG. 1989. Adaptive significance of spination in estuarine crab zoeae. Ecology. 70: 464-482.
Reinhard, EG & PG Reischman. 1958. Variation in Loxothylacus panopaei (Gissler), a common sacculinid parasite of mud crabs, with the description of Loxothylacus perarmatus, n. spp. J. Parisitol. 44: 93-97.
Rodriguez, RA & CE Epifanio. 2000. Multiple cues for induction of metamorphosis in larvae of the common mud crab Panopeus herbstii. Mar. Ecol. Prog. Ser. 195: 221-229.
Ruppert, EE. & RS Fox. 1988. Seashore animals of the Southeast: A guide to common shallow-water invertebrates of the southeastern Atlantic coast. University of SC Press. Columbia, SC. USA. 429 pp.
Ryan, EP. 1956. Observations on the life histories and the distribution of the Xanthidae (mud crabs) of Chesapeake Bay. Am. Midl. Naturalist. 56: 138-162.
Sandifer, PA. 1975. The role of pelagic larvae in recruitment to populations of adult decapod crustaceans in the York River Estuary and adjacent lower Chesapeake Bay, VA. Est. Coast. Shelf. Sci. 3: 269-279.
Silliman, BR & MD Bertness. 2002. A trophic cascade regulates salt marsh primary production. Proc. Nat. Acad. Sci. 99: 10500-10505.
Silliman, BR, Layman, CA, Geyer, K & JC Zieman. 2004. Predation by the black-clawed mud crab, Panopeus herbstii, in Mid-Atlantic salt marshes: further evidence for top-down control of marsh grass production. Estuaries. 27: 188-196.
Voss, GL. Seashore life of Florida and the Caribbean. Dover Publications, Inc. Mineola, NY. USA. 199 pp.
Whetstone, JM & AG Eversole. 1981. Effects of size and temperature on mud crabs, Panopeus herbstii, predation on hard clams, Mercenaria mercenaria. Estuaries. 4: 153-156.
Williams, AB. 1984. Shrimps, lobsters, and crabs of the Atlantic coast of the eastern United States, Maine to Florida. Smithsonian Institution Press. Washington, DC. USA.