''Portunus sayi'', the sargassum swimming crab, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

crab in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Portunidae. It is found in the western

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

and the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

where it makes its home among floating mats of ''

Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae (seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral re ...

'' seaweed. It was named in honour of the American naturalist

Thomas Say Thomas Say (June 27, 1787 – October 10, 1834) was an American entomologist, conchologist, and Herpetology, herpetologist. His studies of insects and shells, numerous contributions to scientific journals, and scientific expeditions to Florida, Ge ...

Description

''Portunus sayi'' grows to a length of about . Its smooth, shiny

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

is nearly twice as broad as it is long and has six frontal teeth on each side. The chelipeds (claws) are larger in males than in females and the spines they bear have orange margins. The carapace, claws and legs are usually pale brown with large white or flesh-coloured blotches but the brown colour may have a purplish or greenish tinge. This crab, like other members of its family, is specially adapted for swimming rather than walking as its fourth pair of legs are modified with flattened, paddle-like surfaces. It swims sideways rather than forwards and can move surprisingly swiftly.

Distribution

''Portunus sayi'' occurs in the western Atlantic Ocean and Caribbean Sea. Its range extends from

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

and the

Gulf of Maine The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America. It is bounded by Cape Cod at the eastern tip of Massachusetts in the southwest and by Cape Sable Island at the southern tip of Nova Scotia in the northeast ...

to southern

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

, Bermuda, the

Bahamas The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the Atlantic Ocean, North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to ...

and the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

. It is found at depths down to about .

Behaviour

''Portunus sayi'' is a swimming crab that lives among the tangled masses of ''

'', a type of brown seaweed that floats in the

Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...

. It is part of a community inhabiting these floating masses which includes

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

, nudibranchs,

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s, hydroids,

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

ns and polychaete worms. Its colouring provides

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...

among the fronds of seaweed through which it hunts or lies in wait to ambush small items of

prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

. It has been shown that the crab chooses ''Sargassum'' spp. over similar seaweeds such as ''

Thalassia testudinum ''Thalassia testudinum'', commonly known as turtlegrass, is a species of marine seagrass. It forms meadows in shallow sandy or muddy locations in the Caribbean Sea and the Gulf of Mexico. Turtle grass and other seagrasses form meadows A meado ...

'' by detecting chemical cues in the water. This crab has also been found as an epibiont of loggerhead turtles along with the goose barnacles ''

Lepas anatifera ''Lepas anatifera'', commonly known as the pelagic gooseneck barnacle or smooth gooseneck barnacle, is a species of barnacle in the family Lepadidae. These barnacles are found, often in large numbers, attached by their flexible stalks to floati ...

'' and ''

Conchoderma virgatum ''Conchoderma virgatum'' is a species of goose barnacle in the family Lepadidae. It is a pelagic species found in open water in most of the world's oceans attached to drifting objects or marine organisms. Description ''Conchoderma virgatum'' has ...

'', various other crabs, sea spiders, tunicates and hydroids. This is not surprising as young loggerhead turtles live among the floating mats of ''Sargassum'' algae feeding on the fauna found there.

References

{{Authority control Portunoidea Crustaceans of the Atlantic Ocean Crustaceans described in 1850