Pachygrapsus crassipes Randall, 1839

Common name(s): Lined shore crab, striped shore crab

Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
    Subclass Eumalacostraca
     Superorder Eucarida
      Order Decapoda
       Suborder Pleocyemata
        Infraorder Brachyura (true crabs)
         Section Brachyrhyncha
          Family Grapsidae
Pachygrapsus crassipes from Laguna Beach, CA.  Carapace width about 3 cm.
(Photo by: Dave Cowles May 1998)
Description:  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 carapaceCarapace to 4.8 cm wide in males, 4.1 cm in females.

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.

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

Depth Range: High and mid intertidal

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

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.  It 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.  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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Dichotomous Keys:
  Kozloff 1987, 1996
  Smith and Carlton, 1975
  Wicksten, 2009

General References:
  Brandon and Rokop, 1985
  Kozloff, 1993
  Morris et al., 1980
  Niesen, 1994
  Sept, 1999

Scientific Articles:

López-Duarte, Paola C., Henry S. Carson, Geoffrey S. Cook, F. Joel Fodrie, Bonnie J. Becker, Claudio DiBacco, and Lisa A. Levin, 2012.  What controls connectivity?  An empirical, multi-species approach.  Integrative and Comparative Biology 52:4 pp. 511-524

Sjoboen, A. D., Dunbar, S.G., and Boskovic, D. 2010. Temporal fluctuations of fatty acids in Pachygrapsus crassipes from Southern California. Journal of Crustacean Biology. 30(2): 257 – 265

Tsuchida, Kohei, Jorgen Lutzen, and Mutsumi Nishida, 2006.  Sympatric three-species infection by Sacculina parasites (Cirripedia: Rhizocephala: Sacculinidae) of an intertidal grapsoid crab.  J. Crustacean Biology 26:4 474-479

General Notes and Observations:  Locations, abundances, unusual behaviors:

Note:  This grapsid crab likes to pinch, and can readily draw blood!  It is more likely to do so than are the Hemigrapsus species.

Another individual, at Little Corona del Mar, CA.  Photo by Dave Cowles March 2005

The underside of this male shows the lack of spots on the chela, the two anterolateral teeth on the carapace behind the eye, and the setae on the legs.
Photo by Dave Cowles, Little Corona del Mar, March 2005
In July 2007 we found the individual below intertidally on Cape Flattery.  It is clearly recognizable as a female Pachygrapsus crassipes though it is hundreds of miles north of its reported range.  Photos were taken by Tyler Shelton
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The two views above clearly show the transverse lines on the carapace and the purplish red and greenish barred color characteristic of Pachygrapsus crassipes.
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There are no purple spots on the propodus of the chelae and there are abundant setae on the legs.  Both of these characteristics distinguish this individual from Hemigrapsus nudus. The carapace has only 2 anterolateral teeth (characteristic of Pachygrapsus) instead of the 3 characteristic of Hemigrapsus.

Cape Alava crab dorsal Cape flattery crab ventral
Although this crab species is seldom found north of central Oregon, in July 2020 I found this individual at Cape Alava, WA. Photos by Dave Cowles

This species seems to be colonizing the Cape Alava region. In 2001 my students and I walked the coast from Cape Alava south to Sand Point and encountered around half a dozen Pachygrapsus crassipes individuals along the way, including this one. The crab was so feisty that I couldn't even get a photo of it without holding it firmly in place. We found the crabs all along the rocky beach to nearly as far south as Sand Point. Photo by Dave Cowles

Authors and Editors of Page:
Dave Cowles (2005):  Created original page