Overview

Brief Summary

Overview

The Sally Lightfoot crab, sometimes called the red rock crab,(1) is a common sight on rocky beaches on the Atlantic and Pacific coastlines of the Americas, from Florida down to Brazil and Mexico down to Chile,(1,2,3,4) as well as on nearby islands such as the Galápagos (1,2,3,4,5) and along the Atlantic coast of Africa.(2,6) Adults, which have carapace widths of around 5-8 centimeters, are generally bright red, brown, or orange with various patterns, while young Sally Lightfoot crabs are darker-colored.(2,4) Sally Lightfoot crabs spend most of their time hiding away in rock crevices,(4,7) but when they come out to feed—primarily during low tide(4,5,7) and during less sunny parts of the day (3)—they move with the remarkable agility and speed that give them their common name.(2,4) While they feed, powerful waves often crash over them, but they are able to withstand these by flattening themselves against rocks and holding on tightly.(2,4) Although these crabs mainly eat red and green algae,(2,4,5) they will eat practically anything they can get,(4) including mussels, barnacles, other crabs, young sea turtles, dead fish, and the young of seabirds such as boobies.(3,4) They also clean the beach of other material such as broken eggs and bird and bat droppings.(3,4) Through their role as predators, grazers, and cleaners, and also through their role as prey for many animals including large birds, octopuses, Kemp’s Ridley sea turtles, and chain moray eels,(4) Sally Lightfoot crabs can play an important part in coastal ecosystems.(3,5)

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Introduction

Sally Lightfoot is the name of a type of crab that lives on the Atlantic and Pacific coastlines of the Americas, from Florida down to Brazil and Mexico down to Chile,(1,2,3,4) as well as on nearby islands such as the Galápagos (1,2,3,4,5) and along the Atlantic coast of Africa.(2,6) Their backs can measures about 5-8 centimeters across, and their body is bright red with various patterns (though their bodies are darker-colored when they are young), and have ten legs.(2,4) Sally Lightfoot crabs, also known as red rock crabs(1) (although the adults can really be many colors from red to orange to brown(4)), spend most of their time hiding away in rock crevices.(4,7) But when they come out to feed—mainly during low tide (4,5,7) and less sunny parts of the day (3)—they move with the remarkable agility and speed that give them their name, “Sally Lightfoot.”(2,4) While they eat, powerful waves often crash over them, but they survive this by flattening themselves against rocks and holding on tightly.(2,4) These crabs mainly eat red and green algae,(2,4,5) but will gobble down practically anything they can get,(4) including mussels, barnacles, other crabs, young sea turtles, dead fish, and the young of seabirds such as boobies.(3,4) Their big appetite means that they also help clean the beach of material such as broken eggs and dried bird and bat droppings.(3,4) Through their role as predators, grazers, and cleaners, and also through their role as prey for many animals including large birds, octopuses, Kemp’s Ridley sea turtles, and chain moray eels,(4) Sally Lightfoot crabs can be an important part of their environment.(3,5)

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Distribution

Red rock crabs can be found along coasts of subtropical and tropical North America, South America, and the islands occuring within this range in both the Pacific and Atlantic Oceans. They are most commonly found in coastal areas of Baja, California, from Mexico to Peru, Ecuador, the Caribbean, Brazil, Florida, and the Galapagos Islands.

Biogeographic Regions: nearctic (Native ); neotropical (Native ); oceanic islands (Native ); atlantic ocean (Native ); pacific ocean (Native )

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Florida to Brazil and Mexico to Peru; Galapagos Islands (Henderson 2002).

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Physical Description

Morphology

Red rock crabs are vividly multi-colored. Adults are typically bright yellow and red with black stripes around the edges of their carapaces and black or green dots near their eyes. Leg joints are often black or a dark green color, each leg ending with a bright orange or yellow tip, and claws are typically bright red. Their underbellies are usually pale white. These crabs are typically darker in color as young adults, growing brighter with age. Carapaces range in size from 5-8 cm in width. They have four large segmented walking legs with spine-like projections near the tip of each leg, and two arms with pinchers. They have two eyes on short stalks at the fronts of their bodies. Males tend to be slightly smaller than females, and their right claws are slightly larger than their left claws.

Larvae (zoea) are about 0.5 mm long and have smooth bodies with long spines and a slender, curved abdomen ending in a forked telson. Their abdomens have five somites, eight legs, two arms with minimal claws and sessile eyes. They have four antennae on their heads.

Range length: 5 to 8 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger; sexes shaped differently

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Grapsus grapsus has a carapace up to ~8 cm. It is highly variable in color and pattern, but often bright red, orange, and brown; young individuals are dark brown or black.

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Ecology

Habitat

St. Peter and St. Paul Archipelago Habitat

Among other ecoregions, this taxon occurs in St. Peter and St. Paul Rocks, a set of small rocky islands far out in the Atlantic Ocean between Brazil and the coast of West Africa. In particular, there are five islets, five very large rocks and a series of smaller skerries that comprise this formation.The rock type of this formation is ultramafic and not volcanic.

This is one of the few places on Earth where an underwater oceanic ridge breaks through the surface of the sea. This formation, also known as St. Peter and St. Paul Archipelago, is the second tallest deep sea mountain or megamullion. These isolated rocks function as a biogeographic oasis in the deep ocean, providing a prime niche for marine life to prosper nearer the ocean’s surface. While the islands are virtually devoid of terrestrial vegetation, the rich marine flora and fauna provides a food source to seabirds that reside and breed here.

Isolation from the mainland provides a habitat of significant ecological and biogeographical interest. More than 800 kilometers from South America, St. Peter and St. Paul Rocks (0°56’N, 29°21’W) land area is estimated to be only 15,000 square metres. Composed of mylonitic peridotite, the submarine mountain of which these rocks are the pinnacles extends 4000 metres into the ocean depths. St. Peter and St. Paul Rocks were  visited by Charles Darwin in 1832 on the first Beagle expedition.

The structure of the islets is a rugged serpentine surface, consisting of numerous fissures, pinnacles and ridgelines. The meager terrestrial vegetation that does occur includes simplistic marine grasses, mosses, fungus and algae. A filamentous blue-green algae, Lyngbya spp, and a minute green algae as Stichococcus bacillaris are example flora.The ocean floor structure in the vicinity of the formation is very irregular as well as steep and rocky; silt bottoms do not occur to the north and south until attaining a depth of approximately three km.

While terrestrial flora is scarce, the isolated islands provide habitat for a rich benthic and littoral marine biota. This food source supports many seabirds, which are the only vertebrate wildlife found on the islands. Breeding seabirds found on the Rocks during the 1971 survey included Brown booby (Sula leucogaster), Brown noddy (Anous stolidus), and Black noddy (Anous minutus). All life-cycle stages of the booby were found during this survey, suggesting that their breeding was aseasonal. The bird eggs often fall prey to Sally Lightfoot Crabs (Grapsus grapsus), a marine invertebrate that is present in large numbers on the islets. The invertebrate element of the Rocks’ food chain primarily consists of microbial feeders. These include protozoa, nematodes (Acrobeloides, Diploscapter and Panagrolaimus genera), bdellodes rotifers, and certain mites (Scheloribates spp.).

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Adult red rock crabs live along rocky shorelines, usually at or above the spray line in tropical and subtropical North America, South America, and islands occuring around this latitude in both the Pacific and Atlantic oceans. When it comes time for eggs, carried by females, to hatch, females go to a calm shallow area so larvae can drop straight into the water. Red rock crab larvae are free swimming in shallow waters just off-shore. After they metamorphose, juveniles makes their way back to rocks on the shore, their primary habitat.

Range elevation: 0 to 5 m.

Average elevation: 1 m.

Habitat Regions: tropical ; terrestrial ; saltwater or marine

Aquatic Biomes: coastal

Other Habitat Features: intertidal or littoral

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Depth range based on 5 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 1 - 1
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Rocky shorelines and beaches at and above the sprayline (Henderson 2002).

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Trophic Strategy

Red rock crabs feed on sponges, mollusks, crustaceans, fishes, carrion (mainly seals and birds), young sea turtles, bird eggs and droppings, algae, and bat guano. As larvae, they feed on phytoplankton. Most food is obtained by scavenging along rocks and the shoreline. Live fish may be caught in shallow waters with their claws and mollusks, such as clams, may be found during low tides. These crabs are known to feed on ticks that they remove from live marine iguanas. They have been known to resort to cannibalism when populations densities are high or food is scarce. Red rock crabs use their claws to scrape food off rocks or capture live animals as well as to move the food into their mouths, and can break open tough material like mollusk and crab shells or corals that may wash ashore.

Animal Foods: birds; reptiles; fish; eggs; carrion ; terrestrial non-insect arthropods; mollusks; aquatic crustaceans; other marine invertebrates

Plant Foods: algae; phytoplankton

Other Foods: detritus ; dung

Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Eats non-insect arthropods, Molluscivore , Eats other marine invertebrates, Scavenger ); herbivore (Algivore); omnivore ; planktivore ; detritivore ; coprophage

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Associations

Red rock crabs feed on dead animals and algae, cleaning up beaches and rocks along coastlines. They help control some bird populations by eating their eggs. They also provide a source of food for many animals that live along coastlines.

These crabs have been known to pick ticks from marine iguanas, suggesting a mutually beneficial relationship between these species.

Red rock crabs are hosts to a number of parasites, including isopods.

Ecosystem Impact: biodegradation

Mutualist Species:

  • Marine iguana (Amblyrhynchus cristatus)

Commensal/Parasitic Species:

  • Lobocepon sp. (Family Bopyridae, Order Isopoda)

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These crabs have many predators including a variety of birds, octopuses, eels, fishes, and cats. They try to avoid predation by moving quickly and hiding in rock crevices during daytime hours. When cornered, they will shoot a stream of water to scare a predator away, pinch with their claws, or drop a leg in order to escape. They rely on their thick carapaces for defense.

Known Predators:

  • Brown Booby (Sula leucogaster)
  • Galapagos lava heron (Butorides striata sundevalli)
  • House cat (Felis catus)
  • Octopus (Class Cephalopoda, Phylum Mollusca)
  • Wahoo (Acanthocybium solandri)
  • Yellowfin Tuna (Thunnus albacares)
  • Little banded eel (Echidna catenata)
  • Moray Eel (Gymnothorax pictus)
  • Kemp's ridley sea turtle (Lepidochelys kempii)

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Grapsus grapsus has been reported as prey of a variety of animals including the Galapagos Lava Heron (Butorides striata sundevalli) (Kushlan 2009) and other large birds, the chain moray (Echidna catenata) (Sazima and Sazima 2004), octopus (Octopus sp.) (Sazima and de Almeida 2009), and Kemp's Ridley sea turtle (Lepidochelys kempii) (Ernst and Lovich 2009).

Food consists largely of grazed algae (see, e.g., Vinueza et al. 2006), but G. grapsus is an omnivorous and opportunistic feeder, consuming items as diverse as bat guano and probably dead bats (Lopez-Foment 1981, cited in Arroyo-Cabrales and Jones 1988), green sea turtle hatchlings (Chelonia mydas) (Ernst and Lovich 2009), masked booby chicks (Sula dactylatra) (Anderson 1989), and food remains, broken eggs, and dead birds in Brown Booby (Sula leucogaster) colonies (Gianuca and Vooren 2007).

Beebe (1924) reported G. grapsus removing (and presumably consuming) ticks (Amblyomma darwini) from a Marine Iguana (Amblyrhynchus cristatus). This may indicate a symbiotic relationship benefiting both crab and lizard.

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Known predators

Grapsus grapsus is prey of:
Actinopterygii

Based on studies in:
Barbados (Littoral, Rocky shore)

This list may not be complete but is based on published studies.
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Known prey organisms

Grapsus grapsus preys on:
detritus
Porifera
Spirobranchus giganteus
Ectoprocta

Based on studies in:
Barbados (Littoral, Rocky shore)

This list may not be complete but is based on published studies.
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Life History and Behavior

Behavior

These crabs communicate using touch, chemical signals, and visual cues. Antennae are used by larvae as tactile receptors. Adults have fine spine-like projections near the tip of each leg, which are used for chemoreception (pheromones) as well as sensing vibration and other tactile input. This species has compound eyes and use their acute vision to find prey.

Communication Channels: visual ; tactile ; chemical

Other Communication Modes: pheromones

Perception Channels: visual ; tactile ; vibrations ; chemical

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Behaviour

Johnson (1965) studied Grapsus grapsus on Oahu, Hawaii, and found that crabs in the study area spent nearly two thirds of their time inactive and hiding in crevices and nearly 20% of their time feeding. They were most active during low tide.

Graspus graspus often feed among rocks swept by surf, flattening themselves against the rock just before each wave hits. These crabs have complex intraspecific visual displays and displaying individuals are the last to prepare for each wave and the first to rise up again after each wave (Wright et al. 1968). When moving about, G. grapsus is strikingly fast and agile.

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Life Cycle

Females carry their eggs under their bodies until they hatch, when they help to release larvae from eggs by using their chelae to disturb their egg mass and wave their bodies in shallow water. After hatching, larvae swim out to deeper waters where they consume phytoplankton and undergo a series of quick molts. More body segments are added after each molt, and two appendages, used for swimming, are added to each new segment. Eventually (an exact number of molts is not known) larvae undergo metamorphosis, becoming juveniles. Juveniles are similar in appearance to adults but are smaller and darker, usually dark green or black with dark red limbs. Juveniles make their way back to rocky shorelines, where they feed as adults and continue to grow by molting, achieving greater size and brighter coloration with each molt. After this puberty molt, the chelae of males grow quickly and females' abdomens become larger in preparation to hold eggs. Adults grow throughout their lives, with longer periods of time between each molt as they age. This species can regenerate lost limbs.

Development - Life Cycle: metamorphosis ; indeterminate growth

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Life Expectancy

Red rock crabs are known to live for up to 10 years in captivity. Average lifespan in the wild is unknown and limited mainly by predation.

Range lifespan

Status: captivity:
10 (high) years.

Typical lifespan

Status: captivity:
5 to 10 years.

Average lifespan

Status: captivity:
7 years.

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Reproduction

During courtship, males will battle for females by first facing each other then side stepping right and left in tandem while touching claws. If neither crab retreats, one crab will lunge at the other and try to grab his rival's claws and break them off; if this occurs, the retreating crab is chased away by the victor, who now has access to a nearby female. This male deposits his sperm into the spermathecae of athe female; the release of sperm is aided by secretions from gonopod tegumental glands, which lubricate the narrow ejaculatory canal and thin out the ejaculate. After receiving sperm, females release their fertilized eggs, storing remaining sperm in their spermathecae. Eggs remain suspended on a female's belly for protection until hatching. Females will only mate again when all stored sperm has been used, which is dependent on how many eggs are produced at a time. While females will only mate with one male at a time, males and females may have multiple partners over a breeding season.

Mating System: polygynandrous (promiscuous)

Breeding occurs year round, particularly in more tropical ranges, but egg hatching seems to coincide with full moons. Males mate often but must wait 10-20 days to regenerate sperm. Females mate less often than males, only when stored sperm has been depleted; depletion time depends on how many eggs are produced, anywhere from 20-100 per clutch, which is dependent on resource abundance and female size. Females molt shortly following hatching a clutch of eggs and will lay eggs again soon after, typically every 24 days. Females carry eggs on their underbellies. Eggs may take up to three weeks to hatch, at which time embryos are aided in hatching by females. Exact age at sexual maturity is unknown, although a puberty molt has been noted at a carapace length of 51.4 mm for males and 33.8 mm for females. After mating, males and females return to their solitary lifestyles.

Breeding interval: Sally Lightfoot crabs may breed multiple times throughout the year.

Breeding season: Breeding season for this species is year-round.

Range number of offspring: 20 to 100.

Average gestation period: 3 weeks.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization

Male red rock crabs exhibit no parental involvement following fertilization. Females carry fertilized eggs underneath their bodies to protect them from predators and keep them out of direct sunlight. Ocean spray and water from females' bodies keep her eggs moist. When it is time for eggs to hatch, females aid this process by rubbing them between their bodies and a rough surface, over shallow water. Larvae drop into the water and are completely independent.

Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female)

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Growth

Development

Guerao et al. (2001) describe the first zoeal larval stage of G. graspus and discuss implications regarding relationships with close relatives.

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Physiology and Cell Biology

Physiology

Grapsus grapsus is an excellent osmoregulator: it can maintain the water balance of its haemolymph (internal body fluid) within narrow limits in the face of external salinity ranging from 50% to 125% (Evans 2009) or 150% (Little 1990) seawater. This allows it to function well in a wide range of microhabitats along the shoreline.

Beninger and Larocque (1998) describe an accessory sex gland that in Grapsus grapsus produces a neutral mucopolysaccharide which they suggest may function (1) as a lubricant to reduce mechanical wear of the ejaculatory canal by the second gonopod during copulation, and (2) to reduce the viscosity of the ejaculate from the vas deferens as it enters the narrow ejaculatory canal.

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Grapsus grapsus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 5
Species With Barcodes: 1
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Conservation

Conservation Status

This species has not been evaluated by IUCN and is not currently considered endangered or threatened.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

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Relevance to Humans and Ecosystems

Benefits

If bothered, these crabs may give a painful pinch or squirt water on their antagonizers. Other than these very minor, avoidable problems, this species presents no adverse effects to humans.

Negative Impacts: injures humans

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Red rock crabs are used, alive or dead, as bait for shoreline fishing. They also help maintain clean shorelines, which is particularly important in areas that rely on tourism. They are sometimes available in the pet trade.

Positive Impacts: pet trade ; ecotourism

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Wikipedia

Grapsus grapsus

For other uses of "red rock crab", see Red rock crab (disambiguation).

Grapsus grapsus is one of the most common crabs along the western coast of the Americas. It is known variously as, "red rock crab", "abuete negro", and along with crabs such as Percnon gibbesi as, "Sally Lightfoot".

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]

Santa Cruz Island, Galapagos Islands

Ecology and behaviour[edit]

Two juveniles in the Galápagos Islands


Adult in the Galápagos Islands

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.

G. grapsus has been observed in an apparent cleaning symbiosis taking ticks from marine iguanas on the Galápagos Islands.[5]

Grapsus grapsus was collected by Charles Darwin during his voyages on HMS Beagle,[6] and also by the first comprehensive study of the fauna of the Gulf of California, carried out by Ed Ricketts, together with John Steinbeck and others. Steinbeck records:[7]

Many people have spoken at length of the Sally Lightfoots. In fact, everyone who has seen them has been delighted with them. The very name they are called by reflects the delight of the name. These little crabs, with brilliant cloisonné 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. They escape the long-handled net, anticipating from what direction it is coming. If you walk slowly, they move slowly ahead of you in droves. If you hurry, they hurry. When you plunge at them, they seem to disappear in a puff of blue smoke—at any rate, they disappear. It is impossible to creep up on them. They are very beautiful, with clear brilliant colors, red and blues and warm browns.



Man reacts peculiarly but consistently in his relationship with Sally Lightfoot. His tendency eventually is to scream curses, to hurl himself at them, and to come up foaming with rage and bruised all over his chest. Thus, Tiny, leaping forward, slipped and fell and hurt his arm. He never forgot nor forgave his enemy. From then on he attacked Lightfoots by every foul means he could contrive and a training in Monterey street fighting has equipped him well for this kind of battle). He hurled rocks at them; he smashed at them with boards; and he even considered poisoning them. Eventually we did catch a few Sallys, but we think they were the halt and the blind, the simpletons of their species. With reasonably well-balanced and non-neurotic Lightfoots we stood no chance.

References[edit]

  1. ^ a b c Peter Davie (2012). "Grapsus grapsus (Linnaeus, 1758)". World Register of Marine Species. Retrieved October 21, 2012. 
  2. ^ G. Guerao, C. D. Schubart & J. D. Cuesta (2001). "The first zoeal stages of Grapsus grapsus (Linnaeus) and Geograpsus lividus (H. Milne Edwards) (Decapoda, Brachyura, Grapsidae) from the western Atlantic" (PDF). Nauplius 9 (2): 111–121. 
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