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Libinia dubia in a seagrass bed with various species of macroalgae. Photo L. Holly Sweat, Smithsonian Marine Station at Fort Pierce.





Libinia dubia camouflaged with macroalge on carapace and legs. Photo L. Holly Sweat, Smithsonian Marine Station at Fort Pierce.





Close-up of hooked setae on the carapace of L. dubia. Photo L. Holly Sweat, Smithsonian Marine Station at Fort Pierce.

Species Name: 
Libinia dubia H. Milne Edwards 1834

Common Name:
Longnose Spider Crab

Species Description:
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).

Regional Occurrence:
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 1964).

IRL Distribution:
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).

III. LIFE HISTORY & 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.

Abundance:
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.

Reproduction:
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.

Embryology:
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.

IV.  PHYSICAL TOLERANCES

Temperature:
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).

Salinity:
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).

V.  COMMUNITY ECOLOGY

Trophic Mode:
Corrington (1927) 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).

Predators:
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).

Parasites:
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).

Associated Species:
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).

VI. SPECIAL STATUS

Special Status:
None

VII.  REFERENCES

Abele, LG & W Kim. 1986. An illustrated guide to the marine decapod crustaceans of Florida, Part 2. Florida State Univ. Tallahassee, FL, USA. 760 pp.

Bland, CE & HV Amerson. 1974. Occurrence and distribution in North Carolina waters of Lagenidium callinectes Couch, a fungal parasite of blue crab ova. Chesapeake Sci. 15: 232-235.

Corrington, JD. 1927. Commensal association of a spider crab and a medusa. Biol. Bull. 53: 346-350.

Dragovich, AJ & JA Kelly, Jr. 1964. Ecological observations of macro-invertebrates in Tampa Bay, Florida. Bull. Mar. Sci. 14: 74-102.

Enzenross, R & L Enzenross. 2000. Non-Mediterranean crustaceans in Tunisian waters (Decapoda, Macrura and Brachyura). Crustaceana 73: 187-195.

Frick, MG, Williams, KL, Markesteyn, EJ, Pfaller, JB & RE Frick. 2004. New records and observations of epibionts from loggerhead sea turtles. Southeast. Nat. 3: 613-620.

Jachowski, R. 1963. Observations on the moon jelly, Aurelia aurita, and the spider crab, Libinia dubia. Chesapeake Sci. 4: 195.

O’Brien, SB, Landau, M & KW Able. 1995. Seasonal and spatial distribution of two species of spider crab in Great Bay, New Jersey. Am. Zool. 35: 67A.

O’Brien, SB, Landau, M & KW Able. 1999. Sex ratios of two species of spider crabs, Libinia dubia H. Milne Edwards, 1834 and L. emarginata Leach, 1815, in the area of Great Bay, New Jersey. Crustaceana 72: 187-192.

Phillips, PJ, Burke, WD & EJ Keener. 1969. Observations on the trophic significance of jellyfishes in Mississippi Sound with quantitative data on the associative behavior of small fishes and medusa. Am. Fish. Soc. 98: 703-712.

Ramasamy, P, Rajan, PR, Jayakumar, R, Rani, S & GP Brennan. 2006. Lagenidium callinectes (Couch, 1942) infection and its control in cultured larval Indian tiger prawn, Penaeus monodon Fabricius. J. Fish Diseases 19: 75-82.

Ruppert, EE & RS Fox. 1988. Seashore animals of the Southeast: A guide to common shallow-water invertebrates of the southeastern Atlantic coast. Univ. South Carolina Press. Columbia, SC, USA. 429 pp.

Ruppert, EE, Fox, RS & RD Barnes. 2004. Invertebrate zoology: A functional evolutionary approach. Brooks/Cole. Belmont, CA, USA. 963 pp.

Sandifer, PA & WA Van Engel. 1971. Larval development of the spider crab, Libinia dubia H. Milne Edwards (Brachyura, Majidae, Pisinae), reared in the laboratory. Chesapeake Sci. 12: 18-25.

Stachowicz, JJ & M Hay. 1999. Reduced mobility is associated with compensatory feeding and increased diet breadth of marine crabs. Mar. Ecol. Prog. Ser. 188: 169-178.

Stachowicz, JJ & M Hay. 1999. Reduced predation through chemically mediated camouflage: indirect effects of plant defenses on herbivores. Ecology 80: 495-509.

Stachowicz, JJ & M Hay. 2000. Geographic variation in camouflage specialization by a decorator crab. Am. Nat. 156: 59-71.

Tabb, DC & RB Manning. 1961. A checklist of the flora and fauna of northern Florida Bay and adjacent brackish waters of the Florida mainland collected during the period July, 1957 through September, 1960. Bull. Mar. Sci. 11: 552-649.

Tunberg, BG & SA Reed. 2004. Mass occurrence of the jellyfish Stomolophus meleagris and an associated spider crab Libinia dubia, eastern Florida. FL Scientist 67: 93-104.

Voss, GL. 1980. Seashore life of Florida and the Caribbean. Dover Publications. Mineola, NY, USA. 199 pp.

Williams, AB. 1984. Shrimps, lobsters, and crabs of the Atlantic coast of the eastern United States, Maine to Florida. Smithsonian Inst. Press. Washington, D.C., USA. 550 pp.

Report by: LH Sweat, Smithsonian Marine Station at Fort Pierce
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Page last updated: 23 May 2009

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