Distribution[edit]
Grapsus grapsus is found along the Pacific coast of Mexico, Central America, South America (as far south as northern Peru), and on nearby islands, including the Galápagos Islands. It is also found along the Atlantic coast of South America, but is replaced in the eastern Atlantic Ocean (Ascension Island and West Africa) by its congener Grapsus adscensionis.[2]
Description[edit]
Grapsus grapsus is a typically shaped crab, with five pairs of legs, the front two bearing small, blocky, symmetrical chelae. The other legs are broad and flat, with only the tips touching the substrate. The crab's round, flat carapace is slightly longer than 8 centimetres (3.1 in). Young G. grapsus are black or dark brown in colour and are camouflaged well on the black lava coasts of volcanic islands. Adults are quite variable in colour; some are muted brownish-red, some mottled or spotted brown, pink, or yellow.
Taxonomy[edit]
Grapsus grapsus was first described by Carl Linnaeus in the 1758 10th edition of Systema Naturae as "Cancer grapsus".[1]
The species Grapsus grapsus and G. adscensionis were not separated until 1990. The latter is found in the eastern Atlantic, 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.[4]
Ecology and behaviour[edit]
This crab lives amongst the rocks at the often turbulent, windy shore, just above the limit of the sea spray. It feeds on algae primarily, sometimes sampling other plant matter and dead animals. It is a quick-moving and agile crab, and hard to catch. Not considered very edible by humans, it is used as bait by fishermen.