How to Distinguish from Similar Species: Hemigrapsus oregonensis also has 3 anterolateral teeth but no purple spots on the chelipeds and the legs have abundant setae. Pachygrapsus crassipes (Oregon and south) has transverse lines and 2 anterolateral teeth on the carapace.
Larvae in the first zoeal stage can be distinguished from zoea of H. oregonensis because H. oregonensis has lateral projections on only abdominal segment 2 while H. nudus has lateral projections on abdominal segments 2 and 3 (Lee and Ko, 2008).
Geographical Range: Yakobi Island, Alaska to Bahia de Tortuga, Mexico. Uncommon below central CA.
Depth Range: Mostly intertidal
Habitat: Under rocks and in cracks. Also high in some estuaries.
Biology/Natural History: Does not live in burrows, as Hemigrapsus oregonensis often does. The chela of males, as of H. oregonensis and P. crassipes, have a prominent tuft of hairlike setae on the palm. This species is an osmoregulator and can tolerate both hypo- and hyperosmotic conditions. In Puget Sound feeds on diatoms, desmids, and small Ulva and Enteromorpha green algae scraped from rocks with the tips of the chelae. May also feed on a few animal products, such as amphipods and the eggs of Nucella emarginata and other whelks. In Puget Sound, females carrying eggs are found from January to mid-July; especially in April. Female may carry from 400 to 36,000 eggs. This species sometimes has the pasasitic isopod Portunion conformis in the perivisceral cavity, and the eggs may be attacked by the tiny Nemertean worm Carcinonemertes epialti. Predators include gulls white-winged scoters, Anthopleura anemones, and staghorn and tidepool sculpins. Nucella lamellosa seems to be attracted to the scent of this crab but is not known to be a predator.
A related member of this genus, Hemigrapsus sanguineus, that lives in Japan is host to the sacculinid barnacle Sacculina yatsui (Kobayashi et al., 2018. Journal of Crustacean Biology 38:3 pp 329-340. doi 10.1093/jcbiol/ruy020)
Flora and Fairbanks, 1996
Kozloff 1987, 1996
Smith and Carlton, 1975
General Notes and Observations: Locations, abundances, unusual behaviors:
This species seems to be less tolerant of hypoxia than is is H. oregonensis. In places where their range overlap it is usually found higher in the intertidal and on more sandy/less muddy substrate.
A related species, H. sanguineus (Asian shore crab) on the New England coast was shown to prefer animal prey such as small mussels and barnacles, even though it could also feed on algae. When starved or in crowded conditions it ate algae, but if given a free choice it chose invertebrates. The authors speculated that the species may have an important effect on competition and succession among intertidal attached species. Source: Brousseau, Diane J. and Jenna A. Baglivo, 2005. Laboratory investigations of food selection by the asian shore crab, Hemigrapsus sanguineus: algal versus animal preference. J. Crust. Biol. 25(1): 130-134 (abstract)
Authors and Editors of Page:
Dave Cowles (2005): Created original page