Arenaeus cribrarius
speckled swimming crab

Speckled swimming crabs, Arenaeus cribrarius, are found on the Atlantic coast of North, Central and South America, ranging from the state of Massachusetts in the United States to Uruguay. (Tavares, 2009)

Speckled swimming crabs live along sandy beaches in shallow to deep water up to 68 m in depth. They have been found in waters 11 to 28.6 °C in temperature and 27.5 to 35 PSU in salinity. When on land, they prefer the foreshore area of beaches in fine mixed sands with low organic matter. (Edlin Guerra-Castro and Carmona-Suárez, 2007; Tavares, 2009)

The carapace of speckled swimming crabs is twice as wide as it is long and can be as wide as 154 mm. The carapace ranges in color from light reddish brown to olive brown and is covered with many small, rounded white spots. The chelipeds (claws) are short and narrow. They have 4 pairs of short, broad pereopods (walking legs) with yellow tips. The fifth pair of pereopods is flattened and paddle-shaped. The perepods and the lower surface of the carapace are densely covered with hair. Speckled swimming crabs can weigh as much as 45 g. (Tavares, 2009)

Speckled swimming crabs have 4 main stages of life; they begin as planktonic zoea, become megalops, benthic juveniles, and finally adults. Speckled swimming crabs pass through 8 stages as zoea, each lasting 4 to 6 days. After each stage, they molt and develop into the next stage of zoea. The body of zoea primarily consists of the head. They have a single dorsal spine in the middle of the head and a long rostrum extending downward beneath the eyes. Zoea also have a long abdomen. Megalops resemble a tiny lobster. During this stage, the head slightly elongates, the dorsal spine, located posterior to the head, shortens, they eyes become stalked, and small chelipeds develop. The abdomen remains long and has now developed prominent peropods. After 13 days, megalops metamorphose into a juvenile crab, with a prominent carapace with two lateral spines projecting from the outer edges. Juveniles have larger chelipeds and a flattened pair of 5th peropods. If juveniles successfully survive, they eventually become adult crabs. (Stuck and Truesdale, 1988)

Between molting periods, male speckled swimming crabs express a courtship display to attract premolted females. The display intensifies when a potential mate is visually recognized. After a female is chosen, the male grasps the female with his chelipeds and holds her under himself for 25 to 35 days until the female molts. Soon after the female molts, when her shell is still soft, the male inverts her so they are positioned abdomen to abdomen. He penetrates her with specially-modified pleopods, transferring spermatophore packages into her gonopores. After copulation, he continues to carry her for 24 to 36 days until her shell has hardened completely. Speckled swimming crabs are polygynandrous, meaning males and females have multiple mates. (Pinheiro and Fransozo, 1999)

Speckled swimming crabs breed year-round, although breeding is more common in the summer and winter, when water temperature oscillations are reduced. Females can produce between 135,000 and 682,000 eggs. Like other members of the family Portunidae, speckled swimming crabs communicate during the reproductive period, which can occur through visual, acoustic, chemical and tactile cues. Speckled swimming crabs reach sexual maturity when their carapace is between 60 and 64 mm in width, which generally occurs around 60 to 80 days of age. (Pinheiro and Franosozo, 1998; Pinheiro and Fransozo, 1999; Pinheiro and Fransozo, 2002; Pinheiro and Terceiro, 2000)

After copulation, female speckled swimming crabs extrude fertilized eggs and carry the egg mass beneath her abdomen with specially-modified pleopods. Females protect their egg mass and fan it with their pleopods to oxygenate the developing eggs and keep them clean. After larvae hatch and are released into the water column, there is no further parental care. (Pinheiro and Fransozo, 1999)

There is currently little information available regarding the lifespan of speckled swimming crabs.

Speckled swimming crabs are nocturnal and solitary, coming together with other members of their species only to breed. When threatened, they automatically assume a defensive position with their chelipeds raised up in the air. Speckled swimming crabs migrate between shallower and deeper waters as they forage and evade predators. (Edlin Guerra-Castro and Carmona-Suárez, 2007; Frick, 2003)

Speckled swimming crabs in Ensenada de La Vela in the Venezuelan Caribbean have a home range of 16,625 sq m. (Edlin Guerra-Castro and Carmona-Suárez, 2007)

As with other crustaceans, speckled swimming crabs communicate through visual, acoustic, chemical and tactile cues. The associated senses are also used in perceiving the environment. (Pinheiro and Fransozo, 1999)

Speckled swimming crabs primarily eat detritus from the ocean floor. They also eat crustaceans, fish, and molluscs. Like most crabs, speckled swimming crabs are opportunistic scavengers, and they have even been recorded chasing down, capturing, and preying on hatchling loggerhead sea turtles. Speckled swimming crabs bury themselves near the breaker zone and ambush prey that crawl or swim near them, seizing the prey with their chelipeds. Crabs then rebury themselves, which may help to subdue captured prey. (Carmona-Suárez and Conde, 2005; Frick, 2003)

The only known predators of speckled swimming crabs other than humans are two species of sea turtles: loggerhead sea turtles and Kemp's Ridley sea turtles. The camouflaged pattern on their carapace helps to conceal speckled swimming crabs in the sand from predators. Also useful against predators are two strong, sharp, slightly upcurved spines on the side of the body. Additionally, the front edge of their carapace is serrated. Speckled swimming crabs are least vulnerable to predation when fully grown, when their spines and camoflouging pattern are fully developed. (Frick, 2003; Tavares, 2009)

As a scavenger, speckled swimming crabs recycle nutrients bound within dead organisms back into the food web. As a mesopredator, they help maintain invertebrate biodiversity within their community. They also serves as prey for larger predators through all of their developmental stages. Speckled swimming crabs also act as host to parasitic barnacles, including Chelonibia patula, Octolasmis lowei, Octolasmis mulleri, as well as a nemertean worm Carcinonemertes carcinophila imminuta. (Mantelatto, et al., 2003)

Speckled swimming crabs are commercially gathered in Brazil as food and are considered to have an excellent flavor. (Carmona-Suárez and Conde, 2002)

There are no known adverse effects of speckled swimming crabs on humans.

Speckled swimming crabs have not been evaluated by the IUCN or the US Fish and Wildlife Service. They are, however, commercially gathered in Brazil which likely influences population sizes. (Carmona-Suárez and Conde, 2002)