Purple Shore Crab
ExploreAnimal
Purple Shore Crab
hemigrapsus nudus
The Purple Shore Crab (Hemigrapsus nudus) is a common and charismatic inhabitant of the rocky intertidal zones along the Pacific coast of North America. Renowned for its striking coloration, which ranges from deep purple to olive green, this small crustacean is a master of survival in one of the ocean's most volatile environments. During low tide, it can often be found scurrying beneath rocks or sheltering in damp crevices, waiting for the high tide to return. It plays a vital role in coastal ecosystems, acting as both an energetic herbivore scraping algae from rocks and a critical food source for larger marine and terrestrial predators. Its hardy nature and ease of observation make it a favorite for tide pool explorers of all ages.
Habitat: Found in rocky intertidal zones, estuaries, and tide pools along wave-swept shores, typically hiding under rocks or among seaweed.
Appearance
This small crab is easily identified by its smooth, squarish carapace that typically measures 3 to 5 centimeters in width. True to its name, it is most often a rich purple or reddish-brown color, though olive-green variations exist. Its most distinctive features are its large, powerful claws (chelipeds) which are covered in small, dark purple spots and have bright white tips. Unlike other shore crabs in its genus, its legs are entirely hairless, giving it a clean, smooth appearance that lacks the hair-like setae characterizing its close relative, the yellow shore crab.
KingdomAnimaliaPhylumArthropodaClassMalacostracaOrderDecapodaFamilyVarunidaeGenusHemigrapsus
Category
AnimalRarity
Common
Danger
1/5 · Very low
Snaps
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Interesting facts
Female crabs carry their fertilised eggs under their abdominal flap for several months, protecting them until they hatch into swimming larvae.
The bright purple spots on its claws look remarkably like freckles, which helps distinguish it from other local crab species.
The species name 'nudus' refers to the crab's completely smooth legs, which lack the fine hairs found on other shore crab species.
Special abilities
Ability
Aerial Respiration
Can survive out of water for extended periods by breathing air through modified gills, provided they remain damp.
Ability
Autotomy and Regeneration
Can voluntarily shed a limb to escape predators or entrapment, later regenerating the lost limb during subsequent molts.
Ability
Substrate Camouflage
Displays color polymorphism that allows it to blend seamlessly with surrounding rocks, barnacles, and diverse seaweeds.
Diet & Feeding
Primarily feeds on green algae and microalgae scraped from rocks, but will opportunistically consume small invertebrates and carrion.
Primary Foods
- Sea lettuce
- Microalgae
- Small snails
- Marine worms
- Carrion
Foraging Method
- Foraging
Ecological connections
hunts
Sitka Periwinkle
Littorina sitkana
Predates on this snail species in rocky intertidal zones.
eaten by
Ochre Sea Star
Pisaster ochraceus
Preys heavily on purple shore crabs during high tide.
eaten by
Glaucous-winged Gull
Larus glaucescens
Preys on exposed shore crabs during low tide foraging.
Traits
No trait badges are assigned for this object yet.
Also known as
No aliases listed yet.
Collections
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Safety
Danger
1/5 · Very low
No special safety notes yet.
Frequently Asked Questions
How to identify Purple Shore Crab?
The easiest way to identify Purple Shore Crab is to use the Snappit nature identifier app.
What does Purple Shore Crab eat?
Primarily feeds on green algae and microalgae scraped from rocks, but will opportunistically consume small invertebrates and carrion.
Where is Purple Shore Crab usually found?
Found in rocky intertidal zones, estuaries, and tide pools along wave-swept shores, typically hiding under rocks or among seaweed.
How does Purple Shore Crab hunt?
Foraging
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Where to spot
Park28 sightings12 species
Washington, US
Peter Roose Homestead
You might spot Purple Shore Crab, Western Bunchberry, and Mule Deer.
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Park30 sightings12 species
Washington, US
Pioneer Square
You might spot Rock Pigeon, American Crow, and Olympic Gull.
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Park23 sightings7 species
Washington, US
Myrtle Edwards Park
You might spot Ochre Sea Star, Purple Shore Crab, and Strawberry Tree.
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Park25 sightings5 species
British Columbia, CA
Gabriola Sands Provincial Park
You might spot Red Rock Crab, Dungeness Crab, and Salal.
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Park16 sightings5 species
British Columbia, CA
Pacific Rim National Park Reserve of Canada
You might spot Ochre Sea Star and Pacific Banana Slug.
View guide →
Park21 sightings4 species
Washington, US
Saltwater State Park
You might spot Bigleaf Maple, Western Redcedar, and Aggregating Anemone.
View guide →