||Libinia dubia H. Milne Edwards 1834
||Longnose Spider Crab
Libinia dubia belongs to a group of brachyuran crabs commonly
referred to as decorator crabs. Using hooked, Velcro-like setae
on the surface of the carapace, the crabs attach bits of algae and
invertebrates for camouflage. This behavior is most common in juveniles,
and the shells of adult crabs are usually found clean. Under the
decorative covering, the carapace of L. dubia is rounded,
bearing approximately six spines down either side and along the
median line on the dorsal surface (eg. Corrington 1927).
A forked rostrum extends between the eyes, and the overall color
of the body is yellowish to brown (Voss 1980). Long, thin walking
legs originating from the rounded body give the crab the spidery
appearance for which it is named. These legs culminate in curved
points, allowing the crab to cling to various surfaces like rocks
and jellyfishes (Ruppert & Fox 1988).
Potentially Misidentified Species
Three species of Libinia inhabit
the coastal and estuarine waters of the Western Atlantic and Caribbean
Oceans: L. dubia; the portly spider crab, L. emarginata;
and the seagrass spider crab, L. erinacea. The color and
shape of all species are similar, and discrimination between juvenile
specimens can be difficult. However, Libinia dubia and
L. emarginata are distinguished by the number of dorsal
median spines, bearing six and nine, respectively (Abele & Kim
1986). The maximum size of the portly spider crab is also slightly
larger than that of L. dubia (Ruppert & Fox 1988).
The rostrum of young seagrass spider crabs forks more deeply than
L. dubia, and the horns curve toward one another (Abele
& Kim 1986).
HABITAT AND DISTRIBUTION
The longnose spider crab is found in a variety of coastal and estuarine
habitats to approximately 50 m depth (Williams 1984). The native
range of L. dubia extends from Cape Cod to southern Texas,
Bahamas and Cuba. However, in the past decade the species has been
reported in the Mediterranean Sea off the Tunisian coast (Enzenross
& Enzenross 2000), although the exact date and vector of introduction
is unknown. In Florida, L. dubia has been documented as
a common inhabitant of Florida Bay (Tabb & Manning 1961), and
the most prevalent spider crab in Tampa Bay (Dragovich & Kelly
Both adult and juvenile L. dubia are found throughout the
Indian River Lagoon. Juveniles are common in seagrass beds, and
adults may inhabit more open sandy-bottom areas. Juvenile crabs
can also be found attached to the cannonball jelly, Stomolophus
meleagris, which occurs seasonally along the coast and throughout
the IRL (Tunberg & Reed 2004).
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Information on the lifespan and adult growth patterns of L.
dubia is lacking. However, the average carapace diameter for
mature crabs is 6 to 10 cm (Corrington 1927, Ruppert & Fox 1988),
with the length of walking legs adding considerably to the total
body size. As with most species, growth rates are likely dependent
on food availability, environmental conditions and other factors.
The longnose spider crab is a common inhabitant in seagrass beds
and sandy areas, although the abundance of individuals is often
quite low. Some seasonality occurs with the abundance of L.
dubia in more temperate waters. In the northeast United States,
both L. dubia and L. emarginata are found in greater
numbers in fall and spring, becoming scarce in summer and rare in
winter (O'Brien et al. 1999). Although little information
has been collected on the spawning seasons of L. dubia,
it is likely that food availability and/or water temperature plays
a role in abundance of larvae and successful recruitment.
Like other brachyuran crabs, sex can be
determined in Libinia dubia by examining the abdomen. In
females, it is broader and can be tightly flexed to hold the egg
mass, or sponge (eg. Ruppert et al. 2004). On
average, females are also slightly smaller than males (O'Brien et
al. 1999, Tunberg & Reed 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.
Once hatched, the larvae pass through three planktonic
stages, two zoeae and one megalopa, lasting approximately nine days
(Sandifer & Van Engel 1971). The zoeal stages are characterized
by a long dorsal spine and a short rostral spine between the large
eyes. These stages measure 2 to 3 mm in total length. Megalopae
have lost the dorsal spine, the rostral spine is shortened and the
legs are more prominent, creating a total body length of about 2
mm. When a suitable habitat is selected, megalopae swim to the benthos
and metamorphose into juvenile crabs.
Although few studies have been conducted on the physical tolerances
of L. dubia, the prevalence of the species in tropical
waters along with its seasonality in temperate regions, suggests
that the crab has a preference toward warmer temperatures. Locally,
crabs have been found in abundance in association with cannonball
jellies in March (Tunberg & Reed 2004). In the laboratory, larvae
have been successfully cultured between 25.5 and 28.5°C (Sandifer
& Van Engel 1971).
The longnose spider crab can be found in both coastal and estuarine
waters, suggesting a large salinity tolerance for the species. In
the Indian River Lagoon, salinities can fluctuate widely over 20
ppt or greater. In laboratory studies, no salinity preference was
found for L. dubia (O'Brien et al. 1995), although
it is not reported in freshwater. Culture of the crab has been successful
at 22 ppt (Sandifer & Van Engel 1971).
defined L. dubia as a scavenger, feeding on easily procured
plant and animal tissue and detritus. In seagrass beds, the spider
crab consumes macroalgae as a portion of its diet, including Gracilaria
tikvahiae and other algae of the genera Ulva, Hypnea,
Chondria and Padina (Stachowicz & Hay 1999).
When in association with various species of medusae, L. dubia
has been found to feed on the mesoglea, the transparent body tissue
of the jelly (Jachowski 1963, Phillips et al. 1969, Tunberg
& Reed 2004).
As juveniles, spider crabs are commonly
preyed upon by larger fishes including: adult pinfish, Lagodon
rhomboides; juvenile gag grouper, Mycteroperca
microlepis; and oyster toadfish, Opsanus tau (Stachowicz
& Hay 1999). To avoid predation, L. dubia decorates
its shell with unpalatable algal and invertebrate species, including
the brown alga, Dictyota menstrualis (Stachowicz &
Hay 1999), and the sun sponge, Hymeniacidon heliophila
(Stachowicz & Hay 2000). As the crab grows larger than the mouth
gape of its fish predators, its predation risk lowers and it ceases
this decorative behavior (Stachowicz & Hay 1999).
Several marine species can become infected with parasites in the
form of worms, copepods, barnacles and other organisms. One such
relationship has been documented between L. dubia and the
marine fungus, Lagenidium callinectes (Bland & Amerson
1974). The fungus infects eggs of L. dubia; the Atlantic
mud crab, Panopeus herbstii; and the blue crab, Callinectes
sapidus (Bland & Amerson 1974), as well as other commonly
aquacultured species (eg. Ramasamy et al. 2006).
Libinia dubia is a common seagrass inhabitant, and is found
in association with other organisms occurring in this habitat. Although
the longnose spider crab is primarily a benthic species, it has
been associated with several pelagic organisms, including: the loggerhead
sea turtle, Caretta caretta
(Frick et al. 2004); the cannonball jelly, Stomolophus
meleagris (Corrington 1927, Phillips et al. 1969,
Tunberg & Reed 2004); the sea nettle, Chrysaora quinquecirrha,
the sea wasp, Chiropsalmus quadrumanus (Phillips et
al. 1969); and the moon jelly, Aurelia aurita (Jachowski
1963). Locally, the most prevalent association is between L.
dubia and S. meleagris. In 2004, a bloom of cannonball
jellies was studied at and around the Fort Pierce Inlet in the southern
half of the Indian River Lagoon (Tunberg & Reed 2004). Approximately
17% of the jellies sampled contained at least one L. dubia
located under the bell. Most scientists believe that the crabs gain
access to their hosts by attaching when the organisms drift toward
the bottom, or by metamorphosing from larvae to juvenile directly
on the host (eg. Corrington 1927). It is often difficult
to determine the type of symbiotic relationship between species,
but it is believed that the crab gains shelter and protection, transportation,
and food from its hosts. In some instances, L. dubia has
even been found to consume tissue from host jellies (Jachowski 1963,
Phillips et al. 1969, Tunberg & Reed 2004).
No information is available at this time
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Report by: LH
Sweat, Smithsonian Marine Station at Fort Pierce
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Page last updated: 23 May 2009