Purple Shore Crab, Hemigrapsus nudus

Purple Shore Crab, Hemigrapsus nudus. Crab collected out of greater San Diego, California area tidal-pool, November 2008. Size: 7.6 cm (3.0 inches) x 6.3 cm (2.5 inches).

General information: The Purple Shore Crab, Hemigrapsus nudus, is one of the most common crabs along the Pacific Coast the Purple Shore Crab is a member of the Grapsidae Family (a family which includes the infamous Sally Lightfoot). In Mexico they are known as morado congrejo de tierra.

Identification: The Purple Shore Crab are decapod crustaceans with 10 limbs, short eye stalks, powerful claws, and short antennae, with a large shell or carapace covering their bodies. They are characterized by a large squarish carapace that has three teeth following the widely separated fairly large eyes, and walking legs that are not hairy. They have a series of white rectangular spots on their backs. Out of water they are faster and more agile than most crabs. The Purple Shore Crab are dimorphic with the males being larger than the females achieving a maximum length of 5.5 cm (2.2 inches) versus about one half the size, 3.3 cm (1.3 inches). They vary in color from dark purple, to olive-green, to reddish-brown. The claws have distinguishing red spots and white tips. They are most often confused with the Yellow Shore Crab, Hemigrapsus oregonensis (which lack the spotting on the shell).

Habitat and Range:  Purple Shore Crabs are found under rocks high in the intertidal zone of exposed beaches and also in some estuaries and have an extensive range being found from Yakobi Island, Alaska to as far south as Guerrero Negro, Baja California.

Diet: The Purple Shore Crab is an opportunistic purveyor of smaller animals and is also a scavenger of diatoms and algae off the surfaces of rocks during nighttime low tides; they will also venture out onto nearby sandy beaches.

Conservation Status: From a conservation perspective the Purple Shore Crab has not been formally evaluated. However, they are common and of limited interest to most and should be considered to be of Least Concern.

Synonyms:  Grapsus marmoratus, Heterograpsus marmoratus, Heterograpsus nudus, and Pseudograpsus nudus.