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Species Name: Pachygrapsus transversus Gibbes, 1850
Common Name: Mottled Shore Crab
Synonymy: None

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Arthropoda Malacostraca Decapoda Grapsidae Pachygrapsus

    Species Description

    The mottled shore crab, Pachygrapsus transversus, is a small intertidal crab belonging to the family Grapsidae. Members of this family are characterized by squarish carapaces with few spines (Voss 1980). The color of the carapace in P. transversus is dark green to black, and the surface is covered with oblique lines of fine tubercles or bumps (Abele et al. 1986, Ruppert & Fox 1988, Voss 1980). The sides converge toward the posterior end to form a trapezoidal shape, and the area between the eyes is slightly curved and bears no teeth. The claws are brownish to pink or cream, with a smooth upper surface on the movable finger. Teeth are present on the hind margins of the largest joints on the legs. Unlike many crabs, there is no sexual dimorphism in claw size, and the total body size of males is larger than females (Abele et al. 1986).

    Potentially Misidentified Species

    The spray crab, Plagusia depressa, is a grapsid crab with similar features to the mottled shore crab, and can be found in many of the same habitats. The carapace reaches a much larger width of about 2.4 cm, and is variously colored with shades of red, green or orange (Ruppert & Fox 1988). Unlike P. transversus, the body is nearly circular with a toothed front margin, and teeth are found on the front side of the largest segments of the walking legs.


    Regional Occurrence & Habitat Preference

    The mottled shore crab has a wide geographic range, including: the western Atlantic from North Carolina to Uruguay, and Bermuda; the eastern Atlantic to Angola, including the Canary Islands and Cape Verde; Mediterranean; and the eastern Pacific from California to Peru, including the Galapagos Islands (Rathbun 1918). This species had also been introduced to areas such as Copenhagen (Christiansen 1969). The preferred habitat of this crab is as varied as its range. Populations are common in rocky intertidal areas, on wharf pilings and sea walls, and in swamps of the red mangrove, Rhizophora mangle (eg. Abele 1976). However, individuals may be found in virtually any sheltered marine intertidal zone at tropical and subtropical latitudes (Crane 1947).

    IRL Distribution

    The mottled shore crab can be found throughout the IRL in all the habitats described above. However, individuals are probably most abundant among jetty rocks, on buoys and pilings near inlets.


    Age, Size, Lifespan

    The maximum age of P. transversus is unknown, and the lifespan can vary with food availability and environmental factors. The mottled shore crab is a small species, with the maximum reported carapace width of only 1.7 cm (Abele 1986).


    Sexual dimorphism is mostly restricted to abdomen morphology, which is larger in females and used to carry egg broods. However, claw size also differs depending on sex, with larger claws belonging to males (Flores et al. 1998). Both males and females reach sexual maturity at a carapace width of about 0.7 cm (Abele et al. 1986). As with most decapod crustaceans, fertilization occurs during copulation. The process usually takes place at the entrance of a burrow, lasts approximately 10 seconds, and is initiated with a leg touch (Abele et al. 1986). Sperm-filled cases, called spermatophores, are transferred from the male 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 Brazil, ovigerous females were reported throughout the year (Flores et al. 1998), but were most abundant in summer months; whereas, recruitment of young was highest in winter (Flores & Negreiros-Fransozo 1999b). Reproduction occurred continuously in Panama populations, and lasted from November through March in Costa Rica (Crane 1947).


    Larval release is mostly controlled by tidal rhythms, and can occur at high tides during the day or at night (Flores et al. 2007, Morgan & Christy 1994). Once hatched, larvae pass through seven zoeal stages and one megalopa before settling to the benthos and metamorphosing into juveniles (Williams 1984).



    Little is known about the thermal tolerances of P. transversus, but the warm temperate to tropical distribution of the species suggests that it can withstand a wide range of temperatures, reaching a thermal minimum around North Carolina. The hiding behavior of the mottled shore crab in holes and crevices is likely a response to thermal and desiccation stress. Individuals allowed to participate in this behavior on hot days were found to be about 3-4°C cooler than the surrounding air (Abele et al. 1986).


    Information about the salinity tolerances for P. transversus is scarce, but most populations of mottled shore crabs are found in highly saline, coastal waters (Ruppert & Fox 1988).


    Trophic Mode

    The mottled shore crab is omnivorous, feeding on algae and detritus at low tide, interspersed with animal prey, including: porcelain crabs, Petrolisthes armatus and P. tridentatus; fishes; and smaller crabs, including juvenile P. transversus (Abele et al. 1986).


    As a common intertidal organism, P. transversus is preyed upon by both aquatic and terrestrial organisms, including fishes, raccoons, birds and frogs (Abele et al. 1986, Sazima 1971).

    Associated Species

    No known obligate associations exist for P. transversus. However, mottled shore crabs are associated with several organisms common to rocky intertidal areas and mangroves. For extensive lists of other species found in the habitats in which P. transversus occurs, please refer to the 'Habitats of the IRL' link at the left of this page.


    No information is available at this time


    Abele, LG. 1976. Comparative species composition and relative abundance of decapod crustaceans in marine habitats of Panama. Mar. Biol. 38: 263-278.

    Abele, LG, Campanella, PG & M Salmon. 1986. Natural history and social organization of the semiterrestrial grapsid crab Pachygrapsus transversus (Gibbes). J. Exp. Mar. Biol. Ecol. 104: 153-170.

    Christiansen, ME. 1969. Crustacea Decapoda Brachyura. Mar. Invertebr. Scand. 2: 1-143.

    Crane, J. 1947. Intertidal brachygnathous crabs from the west coast of tropical America with special reference to ecology. Zoologica. 32: 69-95.

    Flores, AAV, Mazzuco, ACA & M Bueno. 2007. A field study to describe diel, tidal and semilunar rhythms of larval release in an assemblage of tropical rocky shore crabs. Mar. Biol. 151: 1989-2002.

    Flores, AAV & ML Negreiros-Fransozo. 1998. External factors determining seasonal breeding in a subtropical population of the shore crab Pachygrapsus transversus (Gibbes, 1850) Brachyura, Grapsidae). Invert. Reprod. Develop. 34: 149-155.

    Flores, AAV & ML Negreiros-Fransozo. 1999. Allometry of the secondary sexual characters of the shore crab Pachygrapsus transversus (Gibbes, 1850) (Brachyura, Grapsidae). Crustaceana. 72: 1051-1066.

    Flores, AAV & ML Negreiros-Fransozo. 1999. On the population of the mottled shore crab Pachygrapsus transversus (Gibbes, 1850) (Brachyura, Grapsidae) in a subtropical area. Bull. Mar. Sci. 65: 59-73.

    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.

    Moreira, FT, Harari, J & AAV Flores. 2007. Neustonic distribution of decapod planktonic stages and competence of brachyuran megalopae in coastal waters. Mar. Freshwater. Res. 58: 519-530.

    Morgan, SG & JH Christy. 1994. Plasticity, constraint and optimality in reproductive timing. Ecology. 75: 2185-2203.

    Rathbun, MJ. 1918. The grapsid crabs of America. Bull. US Natl. Mus. 97: 1-461.

    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.

    Voss, GL. Seashore life of Florida and the Caribbean. Dover Publications, Inc. Mineola, NY. USA. 199 pp.

Report by: LH Sweat, Smithsonian Marine Station at Fort Pierce
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Page last updated: 21 August 2009

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