The Striking Stripes of the Zebra Crab

The zebra of the Oceans, the zebra crab. 

The zebra crab is covered in black and white stripes like the zebra, but the similarities end there. 

They may look menacing with their spiky-looking exoskeleton and give off the expression they are well armoured. They are delicate and need a particular home to survive. 

Symbiotic Relationship With the Fire Urchin

The zebra crab spends most of its life on a fire urchin for food and safety. Fire urchins are slow-moving but well-armoured animals covered in 4 cm (1.5 in) long spines. The spines will deliver a painful sting to any animal brave or foolish enough to tackle them. 

The spines can easily come off and embed themselves into an attacking animal, causing severe burning pain for hours. With their mouth located underneath, they slowly eat away at the algae on the coral reef while being well protected. 

The fire urchin is not totally immune from attack. Some predators, like the triggerfish and wolf eel, have adapted to kill them without injuring themselves. But don’t feel bad for the fire urchin; if no animal could keep them in check, the reef would be overrun with them. They can not swim, instead slowly walking around on tubed feet that are around their mouth. 

Zebra crabs are small, usually about 2 cm (0.8 in) in width, with the females slightly larger. The fire urchin can grow to around 25 cm (9.8 in) in diameter, so the zebra crab has plenty of room to run around. The zebra crab has adapted to have a unique joint in its legs so it can cling on to the urchin. 

Females will live their entire life on a single fire urchin, only leaving if the host is attacked and killed. Males travel from urchin to urchin, looking for a mate. 

With the fire urchin protecting the zebra crab, it repays the urchin by eating any parasites on the urchin. The zebra crab also feeds on the host, nibbling on the tubed feet and the tissue at the base of the spines. This does not harm the fire urchin as it can constantly regenerate the lost tubing and tissue. This is the cost the fire urchin has to pay to have a parasite-free body. 

They have been found living on nine different species of sea urchins.

Three Know Species

There are currently three known species of zebra crab that belong to the genus Zebrida. 

• Zebrida adamsii is widespread across the Indian Ocean, the western Pacific Ocean, Australia and Japan. 
• Zebrida brevicarinata is only found in western Australia. 
• Zebrida longispina is only found in western Australia.

All species live at a depth of 5 – 15 m (16.5 – 49 ft). 

Zebra Crab Releasing Her Eggs

The video below shows a female zebra crab releasing her eggs that are attached to her underside which is called her apron. The apron is the folded-under abdomen of a crab.

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