Invertebrate
Thin-shelled Rock Crab
Grapsus tenuicrustatusAlso known as Natal Lightfoot Crab, Lightfoot Crab
Thin-shelled rock crabs are lightning-fast scavengers that scuttle across spray-drenched boulders along tropical Indo-Pacific coastlines. Their flattened bodies and splayed, spine-tipped legs allow them to cling tenaciously to sheer stone surfaces even when hit by powerful crashing waves. Active primarily at night and during low tides, they graze on slippery coats of turf algae while remaining constantly alert to incoming surges and predatory sea birds.
IntertidalNocturnalAgile
—observations
—countries
—peak records
Not EvaluatedConservation statusIUCN Red List categoriesLCNTVUENCREWEXNot Evaluated — not placed on the risk ladderRed List categories, explained →
Diet & preyFilamentous Algae, Encrusting Lichen, Dead Fish
Predators
- Moray Eel
- Pacific Reef Heron
- Day Octopus
ThreatsCoastal development, marine pollution, and trampling by human foot traffic
HabitatsWave-swept rocky shores, cliffs, and tropical coral reef flats
Life span3–5 years
Classification
- OrderDecapoda
- FamilyGrapsidae
- GenusGrapsus
- SpeciesGrapsus tenuicrustatus
Range data is not available yet.
Interaction riskLow
- Low
- Moderate
- High
- Very high
- Why interaction risk is low
- Pincers can deliver a sharp, painful pinch if handled; watch footing on slippery rocks.
Responsible observation
- Observation Timing: Scan wave-splashed rocks around twilight or low tide when foraging activity peaks.
- Footwear Caution: Wear sturdy, slip-resistant reef shoes when exploring rocky splash zones.
Image unavailableNeighbor Predator 
Predator (c) JJ Harrison, some rights reserved (CC BY-SA) · cc-by-sa
Close Relative Nosferattus / CC0 · cc0
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