Hemigrapsus nudus or "Purple Shore Crab"
These small decapods are found in the middle-high intertidal region along the rocky shores of the Pacific. They prefer small rocks or gravel substrate and wedge themselves between larger boulders for protection when the tide has receded. In addition, they have a distinctively dark purple and reddish carapace that helps them to conceal themselves in the dark shadows, a perfect camouflage against its predators (most frequently seabirds). They make a distinctive clicking noise that is audible as you stroll along the intertidal.
Purple shore crabs and their shore crab cousins (Hemigrapsus oregonensus and Pachygrapsus crassipes) are very common residents of the intertidal and are commonly mistaken for one another as they share the same habitat. As the Hermigrapus nudus grows to around 5 cm, it spends the majority of its time feeding on algae and dead animals. Primarily an herbivore, they feed mainly on diatoms and green algae. However, as any scavenger, these crabs are essential in maintaining a stable habitat, by feeding upon other dead intertidal residents.
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