| Grapsus grapsus | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| Infraorder: | Brachyura |
| Family: | Grapsidae |
| Genus: | Grapsus |
| Species: | G. grapsus |
| Binomial name | |
| Grapsus grapsus | |
| Synonyms [1] | |
| |
Grapsus grapsus is one of the most commoncrabs along the western coast of theAmericas. It is known as thered rock crab, or, along with other crabs such asPercnon gibbesi, as theSally Lightfoot crab.
Grapsus grapsus is found along the Pacific coast ofMexico,Central America, andSouth America (as far south as northernPeru), and on nearby islands, including theGalápagos Islands. It is also found along the Atlantic coast of South America, but is replaced in the eastern Atlantic Ocean (Ascension Island andWest Africa) by its congenerGrapsus adscensionis.[2]
Grapsus grapsus is a typically shaped crab, with five pairs of legs, the front two bearing small, blocky, symmetricalchelae (claws). The other legs are broad and flat, with only the tips touching the substrate. The crab's round, flatcarapace is slightly longer than 8 centimetres (3.1 in). YoungG. grapsus are black or dark brown in colour and are camouflaged well on the blacklava coasts of volcanic islands. Adults are quite variable in colour; some are muted brownish-red, some mottled or spotted brown, pink, or yellow.
Grapsus grapsus wasfirst described byCarl Linnaeus in the 175810th edition ofSystema Naturae as "Cancer grapsus".[1]
The speciesGrapsus grapsus andG. adscensionis were not separated until 1990. The latter is found in the easternAtlantic, while the former is not.[3] 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.[citation needed]
This crab lives among the rocks at the often turbulent, windy shore, just above the limit of the sea spray. It feeds onalgae primarily, sometimes sampling other plant matter and sponges (such asclams), crustaceans (including other crabs), fishes, young sea turtles, bird eggs and droppings, bat guano and dead animals (mainlyseals andbirds).[4] As larvae, they feed onphytoplankton.[5] They have been known to resort to cannibalism when populations densities are high or food is scarce.[4] It is an agile crab, capable of leaping,[6] and consequently hard to catch. Not considered very edible by humans, it is used asbait by fishermen. It is preyed upon by the chain moray eel,Echidna catenata, as well as by octopuses.[7][8]
G. grapsus has been observed in an apparentcleaning symbiosis takingticks frommarine iguanas on the Galápagos Islands.[9]
Grapsus grapsus was collected byCharles Darwin during his voyages onHMSBeagle,[10] and also by the first comprehensive study of the fauna of the Gulf of California, carried out byEd Ricketts, together withJohn Steinbeck and others. Steinbeck records:[11]
These little crabs, with brilliantcloisonné 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 [San Lucas], and to a less degree inside the Gulf [of 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.
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