Overview

Comprehensive Description

The Lined Shore Crab (Pachygrapsus crassipes) is common from southern Oregon (U.S.A.) to Baja California (Mexico), where it inhabits the upper portions of rocky shores. Its coloration is variable, ranging from greenish to blackish to reddish with transverse (often green or red) stripes running across the carapace. The large pincers are sometimes red or may have red or purple lines. The body width of a large specimen is about 3 to 5 cm. These crabs live under rocks and in crevices. They feed extensively on algae (e.g., green algae such as Ulva, see Sousa 1979), tearing them up with their pincers. Some animals are eaten as well, including limpets and small crabs. Typically, it feeds by bringing its left and right pincers alternately to its mouth. (Kozloff 1993; Sheldon 1999)

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Biology/Natural History: This crab can be very abundant in its range. It is the most semi-terrestrial of the shore crabs, living highest in the intertidal. Forages in and out of the water, active during the day. They spend at least half their time out of water but return periodically to pools to moisten their gills. They are osmoregulators, and can withstand hypo- and hyperosmotic conditions. Feeds on films of algae and diatoms, which it scrapes off the rocks with the tips of its chelae. May also eat small green algae Ulva and Enteromorpha, brown algae Fucus, and red Endocladia, Rhotoglossum, and Grateloupia. Occasionally eats dead animals or small intertidal invertebrates, and has especially been noted eating limpets. Predators include gulls, raccoons, anemones, and fish. Females ready to mate release crustecdysone, which attracts males. She then molts and becomes soft-shelled. The male and female have a courtship dance, then the male rolls onto his back and the female walks above him so that he can insert his sperm into her oviducts. Ovigerous females are found from March to September in central California; peak reproduction is in June and July.

In central Japan this species can be parasitized by any of three sympatric sacculinid barnacles, Sacculina confragosa, S. imberbis, or S. yatsui (Tsuchida et al., 2006).

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This grapsid crab is different from all other grapsids because of the transverse lines on its carapace and the two teeth (rather than 3) on the anterolateral margin of its carapace. Carapace to 4.8 cm wide in males, 4.1 cm in females.
  • Wicksten,Mary K., 2009. ; Decapod Crustacea of the Californian and OregonianZoogeographic Provinces. ; UC San Diego Scripps Institution of OceanographyLibrary, Scripps Institution of Oceanography. ; http://escholarship.org/uc/item/7sk92dz ;418 pages. ; Published online only. ; This excellent key coversdecapods (crustaceans such as crabs, shrimp, spiny lobsters, hermit crabs,and crayfish) from shallow and deep water from Puget Sound south to thePacific coast of Baja California. ; Includes many subkeys, drawings,and photos. ; No glossary, table of contents, or index. ; Thisis the place to go for the most up-to-date key for decapods. ; MaryWicksten plans to publish an updated version of this key soon.   http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Annotated_Bibliography.html#Wicksten+2009 External link.
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Distribution

Geographic Range

Pachygrapsus crassipes are native to the West Coast of North America between 24°20' and 45° latitude. In the 1890's sightings in Japan and Korea were reported between the 34° and the 37° latitudes. The theory for P. crassipes movement into Japan and Korea is that they were carried over by ships carrying zoea larvae (first stage of the crab development)in the water ballast (Morris,et al 1980;Hui 1992).

Biogeographic Regions: nearctic (Native ); palearctic (Native ); pacific ocean (Native )

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Pachygrapsus crassipes is widely distributed along rocky shores of the eastern Pacific Coast, from Charleston, Oregon, USA, to central Baja California, Mexico. It also inhabits the western Pacific Coasts of Japan and Korea, where it was first reported in 1890. Recent evidence suggests that P. crassipes is expanding its distribution northwards along the eastern Pacific Coast and has been found as far north as Bamfield, Vancouver Island, British Columbia, Canada, since 1997. (Cassone and Boulding 2006 and references therein)

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Geographical Range: Charlston, Oregon to Isla de Santa Margarita, Baja California, + Gulf of California, Japan, Korea (it may have been introduced to Asia)

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Physical Description

Morphology

Physical Description

Pachygrapsus crassipes can be red, purple, or green. The carapace (the back shell) is a boxy shape, it is broader than it is long. A distinctive feature P. crassipes is the series of horizontal lines across the carapace.

In this species, the males are larger than the females. The size difference is noticeable after the crab's carapace reaches the width of 22 mm. After they reach 22 mm sexual dimorphism is noticeable. The female's carapace becomes narrower and shorter than that of a male. The difference of the brachyuran on the abdomen is apparent. Other features that occur is the male chelipeds are 8 percent longer. And the propodite and dactylopodite in males are larger by 10%.

Pachygrapsus crassipes can reach the size of 47.8 mm for males and females the carapace can reach the size of 40.8 mm (Morris,et.al 1980; Mohler,et.al 1997; Hiatt 1984).

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Look Alikes

How to Distinguish from Similar Species: Both Hemigrapsus nudus and H. oregonensis have three teeth on the anterolateral margin of the carapace, plus do not have the transverse lines on the carapace.
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Ecology

Habitat

Pachygrapsus crassipes lives on the rocky coastal shores. They live in the region that extends from upper low tidal zone to the highest-high intertidal zone. They like areas of hard substrate where there are many crevices, loose stones, sand, or mud (the mud cannot be too fine or it will suffocate the crab). The most important requirement is that there needs to be enough food in the area (Hiatt, 1948; Shanks 1995).

Aquatic Biomes: coastal

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The Lined Shore Crab (Pachygrapsus crassipes) is found along rocky shores, in bays, in mussel beds, in estuaries and tidal creeks, and on pilings. Along tidal creeks, this crab may burrow into the soft, sandy banks. It appears at ease both on land and in the water. (Hui 1992; Sheldon 1999)

Pachygrapsus crassipes is found in the high intertidal zone of both bays and exposed coastal habitats of the North Pacific (Cassone and Boulding 2006 and references therein).

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Depth Range: High and mid intertidal

Habitat: Crevices, under rocks, in tidepools and mussel beds. Sometimes in clay burrows, especially in San Francisco Bay.

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Trophic Strategy

Food Habits

Pachygrapsus crassipes is omnivorous, which means it eats both plants and animals. The main diet consists of algae such as the green algae Ulva, and Enteromorpha, or it eats red algae such as Endocladia, Rhodoglossm, and Grateloupia. Brown seaweed such as Fucus. However, Pachygrapsus crassipes also eats diatoms, worms, muscles, Hemigrapsus oregonesis , small dead fish., limpets, snails as in Littorina and Tegula, hermit crabs, and isopods. Pachygrapsus crassipes can also become cannibalistic and eat each other (usually this occurs when they still have their soft-shell after molting).

The predators of Pachygrapsus crassipes are seagulls, rats, raccoons, and humans. Other predators that juvenile and larvae crabs need to watch out for are sea anemones and other fish (Barry & Ehret 1993; Quammen 1984).

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Associations

Nemertean worms of the genus Carcinonemertes are associated with various species of crabs. Although juvenile worms are found on males and immature females, the worms grow to maturity and reproduce only on female crabs brooding eggs. When the worms are abundant they can be important egg predators, consuming large numbers of host eggs. (Roe 1979 and references therein) Carcinonemertes epialti apparently has a wide range of hosts. Roe (1979) found it associated with both Hemigrapsus oregonensis and Pachygrapsus crassipes, but based on her study it appears that the life history of C. epialti is much more closely tied to the life history of H. oregonensis than to that of P. crassipes. Infection rates may be very high: in her study, Roe found worms on about half of P. crassipes individuals and about three quarters of H. oregonensis individuals examined (Roe 1979).

The Rhizocephala is an order of highly specialized parasitic barnacles whose hosts are mainly decapod crustacreans, such as crabs. Rhizocephalans have free-living nauplius and cypris larval stages in the life cycle, as commonly seen in cirripeds. However, the morphology of adult rhizocephalans, which lack segmentation and appendages typical of arthropods, has departed very far from that of most crustaceans. The adult consists of an external reproductive saclike body called the ‘externa’ and a ramifying (i.e., spreading with a branching pattern) nutrient-absorbing root-like body inside the host called the ‘interna’, which is connected by a narrow stalk to the externa. This morphological modification in rhizocephalans is extremely conspicuous. Among rhizocephalans, sacculinids are especially notable for severe biological effects on host crabs. Parasitization by sacculinids induces serious modifications in morphology, behavior, reproduction, and molt cycle of hosts. Although significant modifications in morphology and reproduction of a host are also induced by parasitization by parasitic bopyrid isopod crustaceans, the effects of sacculinids on the host are much more dramatic. Tsuchida et al. (2006) report on three different species of Sacculina parasitizing Pachygrapsus crassipes in Japan: S. confragosa, S. imberbis, and S. yatsui. In their study, the authors found that about a quarter of the 138 P. crassipes sampled were infected; examination of two other crab species (103 Hemigrapsus sanguineus and 113 Gaetice depressus) revealed no sacculinids. (Tsuchida et al. 2006)

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Known predators

Pachygrapsus crassipes (Pachygrapsus crassipes (juv.)) is prey of:
Arenaria melanocephala

Based on studies in:
USA: California, Monterey Bay (Littoral, Rocky shore)

This list may not be complete but is based on published studies.
  • P. W. Glynn, Community composition, structure, and interrelationships in the marine intertidal Endocladia Muricata - Balanus glandula association in Monterey Bay, California, Beaufortia 12(148):1-198, from p. 133 (1965).
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Known prey organisms

Pachygrapsus crassipes (Pachygrapsus crassipes (juv.)) preys on:
Syllis vittata
Syllis spenceri

Based on studies in:
USA: California, Monterey Bay (Littoral, Rocky shore)

This list may not be complete but is based on published studies.
  • P. W. Glynn, Community composition, structure, and interrelationships in the marine intertidal Endocladia Muricata - Balanus glandula association in Monterey Bay, California, Beaufortia 12(148):1-198, from p. 133 (1965).
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Life History and Behavior

Behavior

Behaviour

Both field and laboratory observatins indicate a high level of intraspecific aggression in the Lined Shore Crab, with strong spacing tendencies in tide pool populations. However, when these crabs are out of the water, aggression is much reduced and individuals tend to aggregate (e.g., in rock crevices). (Bovbjerg 1960)

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Movement and Dispersal

Crassipes is a highly aggressive and solitary crab, although not very territorial. When out of water, Crassipes’ aggression is subdued, and multiple Crassipes will coalesce in moist crevices of rock, sand, et cetera. When aggregated in niches of rock, Crassipes is mostly inactive. However, in tide pools, Crassipes displays very different behavior, and will not share space with other Crassipes. Crassipes moves sideways, like other crabs, but is also capable of moving forward at quick speeds.

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Life Cycle

Like many crustaceans, the life cycle of the Lined Shore Crab is complex and includes several phases. Larval development of this species is described in detail by Schlotterbeck (1976). Rice and Tsukimura (2007) provide an illustrated identification key to the zoae larvae of the brachyuran crabs found in the San Francisco Bay (U.S.A.) estuary, including recently inroduced species.

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Reproduction

Pachygrapsus crassipes reproduces sexually. The males and females come to sexual maturity at different stages. The males reaches sexual maturity when the breadth of the carapace is 12 mm, this is about seven months after hatching. The female reaches sexual maturity when the carapace is 15 mm, this occurs between 11 and 12 months after hatching.

The females become ovigerous between the months of April to September. Usually the mating only occurs once a year. However, they have been known to reproduce twice a year. It is unknown why a second reproductive period would occur.

When the eggs are fertilized, they are held under the belly of the female. There can be as much as 50,000 eggs. The crab eggs hatch into zoea larva, which turns into megalopae larva (the size is less than a centimeter), and then into crabs. When P. crassipes are in the crab stage there is a correlation between the size of the carapace and the age. Crabs with the carapace around 13 mm in width can be consider one year old, and crabs between 13 mm and 30 mm are considered to be in the second year. P. crassipes that are larger than this can be considered in the third or fourth year. (Hiatt, 1984; Shanks 1995).

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Conservation

Conservation Status

US Federal List: no special status

CITES: no special status

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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

unknown

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Economic Importance for Humans: Positive

unknown

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Wikipedia

Pachygrapsus crassipes

Pachygrapsus crassipes, known as the striped shore crab or lined shore crab, is a small crab found on rocky and hard-mud shores of the west coast of North to Central America and in the western Pacific in Korea and Japan. In North America, its range spans from Vancouver Island to Baja California, Mexico.[1] The Asiatic population appears to not be invasive but endemic, resulting from a divergence estimated between 0.8 to 1.2 Mya.[1] Typically, this crab will have a brown/purple or black carapace with green stripes. Its carapace is square and can reach 4 to 5 cm in size. The claws are red/purple with a mottled pattern on the upper surface, and white on the lower surface, while its legs are purple and green with a similar mottled appearance.[2]

References[edit]

  1. ^ a b Brian J. Cassone & Elizabeth G. Boulding (2006). "Genetic structure and phylogeography of the lined shore crab, Pachygrapsus crassipes, along the northeastern and western Pacific coasts" (PDF). Marine Biology 149: 213–226. doi:10.1007/s00227-005-0197-9. 
  2. ^ "eNature: FieldGuides: Species Detail". Retrieved August 9, 2008. 
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