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Hemigrapsus nudus
Common name(s): Purple shore crab, purple shore crab, naked shore crab
Size:
Up to 4 - 5.6cm when fully grown.
Range:
Rocky and gravely beaches of western North America, from Alaska to Baja California.
Habitat:
Hemigrapsus nudus is most commonly found in the intertidal and subtidal areas of beaches. Since these crabs main predators are birds, it usually stays under rocks and other forms of shelter. In Washington, H. nudus is most commonly found on the shores of the Pacific coast and the Straight of Juan de Fuca.
Misidentification:
H. nudus shares the same habitat with a number of other small crabs like H. oregonensis, and the Pachygrapsus crassipes. These two crabs can be misidentified with H. nudus, especially P. crassipes who has a similarly round shape carapace. Though the H. nudus does stand out because of its purple to reddish spot on each cheliped.
H. nudus is most likely to be present in exposed rocky areas, whereas H. oregonensis is typical of quiet water and rocky habitats of estuaries. Both species of Hemigrapsus have a nearly rectangle carapace (Kozloff, 2000).
Life History:
Hemigrapsus nudus can range in color from purple to red-brown and spends the majority of its time feeding on algae and dead animals. The males of this species, and other shore crabs, are often seen with a sponge like tissue on the inside of each cheliped. It is unknown as to what this tissue is for. As any scavenger, these crabs are essential in maintaining a stable habitat.
Predators:
Gulls and other seabirds.
References:
Batie, Robert E. (1974). Population structure of the intertidal shore crab Hemigrapsus oregonensis (Brachyura, Grapsidae) in Yaquina Bay, a central Oregon coast estuary. Oregon State University, Ph.D., 1974, Marine Sciences. Ann Arbor, MI.
Kozloff, Eugene. Seashore Life of the Northern Pacific Coast. University of Washington Press: Seattle and London.
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Last updated Thursday, August 24, 2006, by Lisa Ferrier
