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).
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).
Potentially Misidentified Species
Xanthid crabs are a large, often confusing group with subtle differences
between some species. The largest member of this family in the southeast
United States is the edible Florida stone crab, Menippe
mercenaria. Other smaller mud crabs possibly confused with
P. herbstii include: the strongtooth mud crab, Panopeus
bermudensis; Say mud crab, Dyspanopeus
sayi; Florida grassflat crab, Neopanope packardii;
and the flatback mud crab, Eurypanopeus
depressus. Like the Atlantic mud crab, dark color on the
lower finger of all these species extends onto the palm of the claw
(Kaplan 1988). However, the average size of P. herbstii
is significantly larger than any of the following mud crabs.
The carapace of the strongtooth mud
crab reaches a length of 1cm, has four sharp teeth on the
edge of each side, and is dull red in color (Kaplan 1988). The claws
are grayish, with dark lower fingers, white fingertips and a tan
spot at the base.
The carapace of the Say mud crab
reaches a length of 2.1 cm, and is bluish green, brown or buff,
with reddish brown spots on a yellow background (Kaplan 1988). The
first marginal tooth on each side is rounded, and the remaining
teeth are slanted but not sharp.
The Florida grassflat crab
attains a length of 1.3 cm, with claw coloration similar to the
previously mentioned species (Kaplan 1988). The marginal teeth on
the carapace are similar to those of D. sayi, but the last
three marginal carapace teeth are spiny.
The flatback mud crab reaches
a length of 1.8 cm, is mottled grayish or dark olive-brown with
the last three marginal teeth large and sharp (Kaplan 1988). The
fingertips are spoon-shaped, with small teeth at the base of the
HABITAT AND DISTRIBUTION
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
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.
LIFE HISTORY AND POPULATION BIOLOGY
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).
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).
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).
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).
The Atlantic mud crab is usually found throughout estuaries in brackish
waters above 10 ppt (Gosner 1978, Rodriguez & Epifanio 2000).
The diet of the Atlantic mud crab is primarily carnivorous. Individuals prey on
a variety of organisms, including: oysters and clams; crustaceans;
annelid worms; fishes; and the marsh periwinkle, Littorina
irrorata (Castagna & Kraeuter 1977, McDermott 1960,
Silliman & Bertness 2002, Silliman et al. 2004, Whetstone
& Eversole 1981). Larvae of P. herbstii prey upon other
zooplankton, and were successfully reared in the laboratory on a
diet of brine shrimp and rotifers (Harvey & Epifanio 1997).
The Atlantic mud crab is likely preyed
upon by a variety of birds, fishes and larger crustaceans. In North
Carolina, the dominant predator of P. herbstii populations
was the oyster toadfish, Opsanus tau (Grabowski 2004).
Megalopae are consumed by several organisms, including: juvenile
blue crabs, Callinectes sapidus;
common killifish, Fundulus heteroclitus; and grass shrimp,
(Dittel et al. 1996).
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).
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. For extensive
lists of other species found in the habitats in which P. herbstii
occurs, please refer to the 'Habitats of the IRL' link at the left
of this page.
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).
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