''Grapsus grapsus'' is one of the most common

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

s along the western coast of the

Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...

. It is known as the red rock crab, or, along with other crabs such as '' Percnon gibbesi'', as the Sally Lightfoot crab.

Distribution

''Grapsus grapsus'' is found along the Pacific coast of

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

, and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

(as far south as northern

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

), and on nearby islands, including the

Galápagos Islands The Galápagos Islands () are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of sli ...

. It is also found along the Atlantic coast of South America, but is replaced in the eastern Atlantic Ocean (

Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the Atlantic Ocean, South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overs ...

and

West Africa West Africa, also known as Western Africa, is the westernmost region of Africa. The United Nations geoscheme for Africa#Western Africa, United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Gha ...

) by its congener '' Grapsus adscensionis''.

Description

''Grapsus grapsus'' is a typically shaped crab, with five pairs of legs, the front two bearing small, blocky, symmetrical

chelae A chela ()also called a claw, nipper, or pinceris a pincer-shaped organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through Neo-Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds ...

(claws). The other legs are broad and flat, with only the tips touching the substrate. The crab's round, flat

carapace A carapace is a 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 tortoises, the unde ...

is slightly longer than . Young ''G. grapsus'' are black or dark brown in colour and are camouflaged well on the black

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

coasts of volcanic islands. Adults are quite variable in colour; some are muted brownish-red, some mottled or spotted brown, pink, or yellow.

Taxonomy

''Grapsus grapsus'' was first described by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in the 1758 10th edition of ''

Systema Naturae ' (originally in Latin written ' with the Orthographic ligature, ligature æ) is one of the major works of the Sweden, Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the syste ...

'' as "''Cancer grapsus''". The species ''Grapsus grapsus'' and '' G. adscensionis'' were not separated until 1990. The latter is found in the eastern

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

, while the former is not. While the validity of the separation into two species has been questioned, there are constant morphological differences in the colouration of the pereiopods and the form of the first zoea larva, and no evidence for any genetic connection between the two populations, and they are generally treated as separate species.

Ecology and behavior

This crab lives among the rocks at the often turbulent, windy shore, just above the limit of the sea spray. It feeds on

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

e primarily, sometimes sampling other plant matter and sponges (such as

clam Clam is a common name for several kinds of bivalve mollusc. The word is often applied only to those that are deemed edible and live as infauna, spending most of their lives halfway buried in the sand of the sea floor or riverbeds. Clams h ...

s), crustaceans (including other crabs), fishes, young sea turtles, bird eggs and droppings, bat guano and dead animals (mainly seals and

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s). As larvae, they feed on

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

. They have been known to resort to cannibalism when populations densities are high or food is scarce. It is an agile crab, capable of leaping, and consequently hard to catch. Not considered very edible by humans, it is used as bait by fishermen. It is preyed upon by the chain moray eel, '' Echidna catenata,'' as well as by octopuses. ''G. grapsus'' has been observed in an apparent

cleaning symbiosis Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning is often performed for beauty, aesthetic, hygiene, hygienic, Function (engineering), function ...

taking

tick Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, and species, but can become larger when engorged. Ticks a ...

s from

marine iguana The marine iguana (''Amblyrhynchus cristatus''), also known as the sea iguana, saltwater iguana, or Galápagos marine iguana, is a species of Iguanidae, iguana found only on the Galápagos Islands (Ecuador). Unique among modern lizards, it is a m ...

s on the Galápagos Islands. ''Grapsus grapsus'' was collected by

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...

during his voyages on HMS ''Beagle'', and also by the first comprehensive study of the fauna of the Gulf of California, carried out by Ed Ricketts, together with

John Steinbeck John Ernst Steinbeck ( ; February 27, 1902 – December 20, 1968) was an American writer. He won the 1962 Nobel Prize in Literature "for his realistic and imaginative writings, combining as they do sympathetic humor and keen social percep ...

and others. Steinbeck records:

These little crabs, with brilliant
cloisonné Cloisonné () is an ancient technology, ancient technique for decorating metalwork objects with colored material held in place or separated by metal strips or wire, normally of gold. In recent centuries, vitreous enamel has been used, but inla ...
carapaces, walk on their tiptoes, They have remarkable eyes and an extremely fast reaction time. In spite of the fact that they swarm on the rocks at the Cape an Lucas and to a less degree inside the Gulf f California they are exceedingly hard to catch. They seem to be able to run in any of four directions; but more than this, perhaps because of their rapid reaction time, they appear to read the mind of their hunter.

Gallery

Zayapa (Grapsus grapsus), Las Bachas, isla Baltra, islas Galápagos, Ecuador, 2015-07-23, DD 30.JPG, Baltra, Galapagos Islands Zayapa (Grapsus grapsus), Las Bachas, isla Santa Cruz, islas Galápagos, Ecuador, 2015-07-23, DD 25.jpg, Baltra, Galapagos Islands. Zayapa (Grapsus grapsus), Cerro Brujo, isla de San Cristóbal, islas Galápagos, Ecuador, 2015-07-24, DD 152.JPG, Juvenile in San Cristobal, Galápagos. Zayapa (Grapsus grapsus), Cerro Brujo, isla de San Cristóbal, islas Galápagos, Ecuador, 2015-07-24, DD 151.JPG, Adult in San Cristobal, Galápagos. Zayapa (Grapsus grapsus), Punta Pitt, isla de San Cristóbal, islas Galápagos, Ecuador, 2015-07-24, DD 84.JPG, Adult in Punta Pitt (San Cristobal), Galápagos. Zayapa (Grapsus grapsus), Punta Pitt, isla de San Cristóbal, islas Galápagos, Ecuador, 2015-07-24, DD 79.JPG, Group in San Cristobal, Galápagos. Zayapa (Grapsus grapsus), Las Bachas, isla Santa Cruz, islas Galápagos, Ecuador, 2015-07-23, DD 21.jpg, Adult in Baltra, Galápagos. Zayapa (Grapsus grapsus), Punta Pitt, isla de San Cristóbal, islas Galápagos, Ecuador, 2015-07-24, DD 83.JPG, View of the lower part Galápagos Sally Lightfoot crab (Grapsus grapsus).jpg, Adult from the front

References

External links

* * {{Taxonbar, from=Q181075 Grapsidae Crustaceans of the eastern Pacific Ocean Crabs of the Pacific Ocean Crustaceans described in 1758 Taxa named by Carl Linnaeus Marine fauna of the Gulf of California Western Central American coastal fauna Galápagos Islands coastal fauna Western South American coastal fauna Crustaceans of Brazil