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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.
II. HABITAT AND DISTRIBUTION
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.
III. LIFE HISTORY AND
POPULATION BIOLOGY
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).
Reproduction:
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).
Embryology:
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).
IV. PHYSICAL TOLERANCES
Temperature:
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).
Salinity:
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).
V. COMMUNITY ECOLOGY
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).
Predators:
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.
VI. SPECIAL STATUS
Special Status:
None
VII. REFERENCES
& FURTHER READING
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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