Is my Sally Lightfoot Crab dead or has it moulted?

Crabs moult by leaving behind a perfect, empty replica of their exoskeleton. If you find a 'dead' crab, examine it closely; if it is hollow inside and the carapace flips open like a lid, it is a moult. Your real crab will be hiding securely in the rocks while its new shell hardens.

Will a Sally Lightfoot Crab eat my corals?

They are generally considered reef-safe and usually ignore corals. However, if they are starving, they may pick at the polyps of soft corals or steal food intended for large-polyp stony (LPS) corals. Keeping them well-fed prevents this.

Are Sally Lightfoot Crabs aggressive towards fish?

When small, they are completely peaceful. As they reach maximum size, they become more opportunistic and might attempt to catch very small, slow-moving or sleeping fish if they are not receiving enough food.

How do I supplement their diet if my tank has no algae?

You can offer dried seaweed (nori) attached to a clip or rubber-banded to a small rock, along with sinking algae wafers and occasional meaty treats like mysis shrimp.

Why is my crab constantly hiding?

Hiding is natural, especially if the crab has recently moulted, is preparing to moult, or feels threatened by active tank mates. Ensure they have plenty of deep crevices to feel secure.

MarineMarineIntermediate

Sally Lightfoot Crab

Percnon gibbesi

The Sally Lightfoot Crab is a highly active, algae-eating marine invertebrate renowned for its agility and striking flat-bodied appearance.

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Ideal Conditions

Temperature: 23 – 26 °C
pH range: 8.1 – 8.4
Hardness: 14 – 22 dGH
Salinity: 1.023 – 1.025 SG
Adult size: 6 – 10 cm
Standard marine aquarium: 110 litres+
Lifespan: 2 – 3 years
Diet: Omnivore, primarily herbivorous but will opportunistically scavenge meaty foods.
Water flow: Moderate to strong
Preferred setup: Requires mature live rock with deep crevices to shelter in, especially during the moulting process.

About the Sally Lightfoot Crab

Named for its incredibly nimble, almost dancing movement across rocks, the Sally Lightfoot Crab (*Percnon gibbesi*) is a staple in the marine aquarium hobby. Although the common name is sometimes shared with the Galápagos crab (*Grapsus grapsus*), the aquarium trade exclusively offers *P. gibbesi*. Known for its exceptionally flat carapace and long, spidery legs, it is remarkably adept at squeezing into the tightest crevices to evade predators or scavenge for detritus. While celebrated as an industrious cleaner, keepers must respect its opportunistic nature as it matures.

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Is it right for your tank?

Check Sally Lightfoot Crab against a habitat you already keep. We compare water type, temperature, pH, adult size, group needs and everything living there.

Where Sally Lightfoot Crab comes from

Native range

Caribbean Sea, Eastern Atlantic Ocean, Western Atlantic Ocean

Countries / regions

United States, Bahamas, Brazil, Spain, Portugal

Habitat

Shallow coastal reefs, rocky tidal zones, and breakwaters, often hiding within urchin spines or narrow rock fissures.

Originally native to the Atlantic Ocean and Caribbean, it has recently become an established invasive species in the Mediterranean Sea.

Similar species

Emerald Crab
Mithraculus sculptus
Arrow Crab
Stenorhynchus seticornis
Porcelain Crab
Neopetrolisthes maculatus

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Yellow Tang
Zebrasoma flavescens
Large, active, and fully capable of ignoring or avoiding the crab whilst coexisting peacefully.
Great
Ocellaris Clownfish
Amphiprion ocellaris
Stays primarily in the water column or near an anemone, rarely crossing paths with the rock-dwelling crab.
Great
Turbo Snail
Turbo fluctuosus
Armoured adequately to withstand casual investigation and shares the algae-clearing workload.
Great
Clown Goby
Gobiodon okinawae
Very small bottom-dwelling or perching fish may occasionally be targeted by a large, hungry Sally Lightfoot Crab at night.
Compatible with caution
Emerald Crab
Mithraculus sculptus
May compete for food and territory; keeping multiple crab species requires a spacious tank with abundant rockwork.
Compatible with caution
Clown Triggerfish
Balistoides conspicillum
Aggressive predatory fish that will readily dismantle and consume crustaceans.
Not recommended
Dogface Puffer
Arothron nigropunctatus
Possesses a strong beak designed specifically for crushing the shells of crabs and snails.
Not recommended

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