The stone crab, Menippe mercenaria, can be found just below the low tide line from the Atlanic coast of North Carolina to the Gulf coast of Florida. (Beck, April 95)
Adult Menippe mercenaria generally inhabit sub-tidal regions; they burrow under emergent hard substrate or in seagrass beds. Juvenile stone crabs are found nearshore in marine waters on seagrass beds, or around emergent live rocks in highly dense populations. Some juveniles have been caught in deep channels near the Florida coast. The stone crab larvae travel with the zooplankton, upon which they feed, in nearshore marine environments. (Beck, April 95; Bert and Stevely, 1999; Gulf Shores Marine Fisheries Commission, 2001)
Stone crabs have exoskeletons and have a brown and black speckled carapace that is oval, smooth, and convex. The carapace averages 130 mm across in adult females and 145 mm across in adult males. Adult Florida stone crabs have a trunk composed of 14 segments, and 5 pairs of stout walking legs, which have reddish and yellow bands and distal hairs. The first eight segments compose the thorax, and the remaining six segments compose the abdomen. The first set of walking legs develop into an asymmetrical pair of heavy chelipeds that typically make-up 60% of the animal's entire body weight and possess a crushing pressure of 14,000 pounds per square inch.
Juveniles are a dark purplish blue. Younger juveniles have a white spot on the carpus, which is the middle segment of the endopod, or limb. (Raichlen, 2000; Rupport and Barnes, 1994; Williams, 1984; Wu, 1997)
Upon hatching, Menippe mercenaria develops through five zoeal stages, which collectively make up the larval stage. These stages lasts between 14-27 days and are strongly dependent upon water temperature. The stone crab then develops into a post-larval stage that lasts between 1 and 2 weeks. During the larval and post-larval stages the stone crabs live among the zooplankton in nearshore waters. From the post-juvenile stage to when the carapace of the young crab develops to a width of 10 mm, the stone crab is considered to be a post-settlement juvenile. At this time they move away from the zooplankton into areas densely populated with other juvenile stone crabs. These places are usually seagrass beds or areas around emergent live rocks. It will then take the stone crab around 12 months to become a late juvenile, which is described as having a carapace width greater than 10 mm but less than 35 mm across. With a carapace width of 35 mm, the stone crab enters into adulthood. (Gulf Shores Marine Fisheries Commission, 2001)
Most female Menippe mercenaria sexually mature around two years old, and are most likely to breed between the spring and fall. The female carries her eggs in a sac-like mass containing 160,000 to 1,000,000 eggs. Optimum water temperature for ovarian development is around 28 deg C. Menippe mercenaria breeds year-round, although the peak mating season is from August to September in southern Florida. Males may mate with recently molted females. (Gulf Shores Marine Fisheries Commission, 2001; Williams, 1984)
The female carries her eggs in a sac-like mass containing 160,000 to 1,000,000 eggs until they hatch.
From egg to death, male Menippe mercenaria live for approximately 6 years, while the females live to be approximately 7 years old. (Gulf Shores Marine Fisheries Commission, 2001)
Menippe mercenaria is a nocturnal creature that is predominantly found among seagrass beds or burrowed under emergent rock substrates along the North American coast from North Carolina to western Florida. It has been observed that stone crabs migrate seasonally within the Florida Keys, showing higher population densities on the Gulf side during the fall, and the Atlantic side during the spring. Stone crabs have been known to travel up to 30 km in a year. During confrontations with other stone crabs, the males will conduct a ritual display of their claws. Most confrontations are over breeding habitat and food. Male dominance has been correlated with size. If a stone crab's carapace is punctured during fighting, the carapace will regenerate; a bio-chemical phenomena that has intrigued many in the science community. (Beck, April 95; Bert and Stevely, 1999; Raichlen, 2000; Williams, 1984; Wu, 1997)
The stone crab's primary method of communication is visual signaling. Before engaging in an intraspecies confrontation, a stone crab will openly display its massive claws. The larger the claws, the more likely that stone crab will be able to claim the local ideal breeding habitat. (Bert and Stevely, 1999)
As Menippe mercenaria grows and develops, its food habits change. The larvae and pre-juvenile stone crabs are opportunistic carnivores that feed on smaller zooplankton. The juvenile and adult stone crabs are still opportunistic carnivores, but feed on animals that are larger than the zooplankton. Utilizing their massive and powerful claws, adult stone crabs feed on acorn barnacles, hard shelled clams, scallops, and conch. (Gulf Shores Marine Fisheries Commission, 2001; Williams, 1984; Wu, 1997)
The most obvious anti-predator adaptation is the development of massive chelipeds that are capable of exerting 14,000 pounds per square inch of pressure. These claws keep the number of adult stone crab predators to a minimum. The general consensus among experts in the study of Menippe mercenaria believe the low number of natural predators is probably due to the hard exoskeleton of the stone crab, which allows it to survive long enough to pinch and gash the predator's gastrointestinal lining. One species that seems completely unconcerned with the massive chelipeds of the stone crab is the octopus, which is the primary natural predator of the stone crab. Juvenile stone crabs are also depredated by large fish. (Wu, 1997)
The larvae of the stone crab contribute to the nearshore zooplankton population that is critical to feeding larger fish. Federal law protects the stone crab from over-harvesting by man, and there has not been a reported disturbance in the nearshore marine ecosystem since this law was enacted. (Gulf Shores Marine Fisheries Commission, 2001)
Between 3 and 3.5 million pounds of Menippe mercenaria claws are harvested annually in Florida alone. This occupation employs around 4,000 crabbers in Florida, as well as many restaurant employees along the eastern sea-board. Federal law mandates that only one claw per crab be removed (it will grow back in 1-2 years), and that the claw must be at least 6.99 cm (2 and 3/4") from the first joint to the tip of the lower immovable finger. Overall, the stone crab industry generates 12-15 million dollars from Florida to North Carolina. (Raichlen, 2000; Wu, 1997)
Adult M. mercenaria feed primarily on hard shelled molluscs, some of which are also fished for human consumption. The stone crab does not play a significant role in reducing these populations, but they are capable of adversly affecting the industry. (Wu, 1997)
Menippe mercenaria is not endangered, but it is protected by United States Code Title 16, ch. 38, and the Magnuson-Stevens Fishery Conservation and Management Act. These laws recognize the need to regulate trapping of the stone crab, and establish that only one claw may be removed per stone crab (none if it is an ovigerous female) if it is at least 6.99 cm (2 and 3/4") from the first joint to the tip of the lower immovable finger. (Raichlen, 2000)
Menippe mercenaria and its closely related and co-occurring species, Menippe adina, have recently been the subject of much research on hybrid zones and evolutionary speciation. M. mercenaria is sympatic with M. mercenaria along the Gulf Coast of Florida and forms allopatic populations along to the Gulf Coast, all the way to Mexico. These recent studies have provided conflicting evidence as to when the two species were isolated, and what effects recent contact has had on the development of each species. (Beck, April 95)
Renee Sherman Mulcrone (editor).
Michael Brinkman (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
the nearshore aquatic habitats near a coast, or shoreline.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
fertilization takes place within the female's body
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats plankton
mainly lives in oceans, seas, or other bodies of salt water.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
uses sight to communicate
breeding takes place throughout the year
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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Bert, T., J. Stevely. 1999. Population Characteristics of the stone crab, *Menippe mercenaria*, in Florida Bay and the Florida Keys. Marine Science, 44(1): 515.
Gulf Shores Marine Fisheries Commission, 2001. "Summary table of the Stone Crab, *Menippe mercenaria*,: Life History for the Gulf of Mexico" (On-line). Accessed 11/04/04 at http://www.gsmfc.org/pubs/habitat/tables/stonecrab.pdf.
Meinkoth, N. 1981. The Audobon Society Field Guide to North American Seashore Creatures. New York City: Knopf.
Raichlen, S. 2000. The Perfect Crab: It's all claw. NY Times, 51258: F1, F8.
Rupport, E., R. Barnes. 1994. Invertebrate Zoology 6th edition. USA: Sanders College Publishing.
Williams, A. 1984. Shrimps, lobsters, and crabs of the Atlantic coast of the Eastern United States, Maine to Florida. Washington, D. C.: Smithsonian Institution.
Wu, C. 1997. Crab Crackers. Science News, 151(8): 122.