TankBud

Blue spot urchin

Astropyga radiata

Also known as Blue spot star urchin, Blue spot longspine urchin, Radiant sea urchin, Red urchin, Red radiating hatpin urchin, Blue-spotted urchin

SaltwaterInvertebrate

Blue spot urchin (Astropyga radiata)
(c) Dan Schofield, some rights reserved (CC BY) · cc-by

Care at a glance

Temperature
72–82°F
22–28°C
pH
8.1–8.4
Adult size
7.9 in
20 cm
Minimum tank
100 gal
380 L
Temperament
Peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Omnivore
Difficulty
Medium
Breeding
No record
Rarity
Rare
Reef safe
Reef safe with caution
Family
Diadematidae
Origin
Indo-Pacific lagoons and sandy bays, East Africa to Hawaii

Overview

The blue spot urchin is a big, peaceful algae grazer for a large, mature tank. It suits a keeper with a little experience.

Did you know

In the Indo-Pacific, the urchin crab Dorippe frascone picks up a live blue spot urchin and carries it on its back like a shield. The crab walks around under a venomous umbrella that predators leave alone. The urchin gets carried to fresh feeding grounds, so both animals get something out of the deal.

Caring for the blue spot urchin

Give the blue spot urchin a wide sand floor with rock it can shelter under, in a tank of at least 100 gal (380 L). It needs that room because an adult is the size of a dinner plate. Lock the rockwork together, since it will shove loose pieces aside. Keep it in a mature system with plenty of film algae.

Hold the water at 72 to 82°F (22 to 28°C) with a pH of 8.1 to 8.4, and keep nitrate low. Never use copper. Drip acclimate it slowly, and move it with tongs or a container, never bare hands.

It grazes mainly on algae, but it also eats sponges, bivalves, small snails and dead animals. Feed it dried seaweed or algae pellets several times a week.

The blue spot urchin is peaceful and safe with fish, but that wider diet makes it a caution in a reef. Its bulk also topples frags. Triggers, puffers and large wrasses will eat it.

Good to know

Astropyga radiata is a diadematid urchin, in the same family as the long-spine urchins. The test is broad and flattened, with spines only about 4 cm long arranged in five V-shaped bands. The bare zones between the bands carry rows of iridescent blue dots. It is light sensitive and points its spines at anything that casts a shadow. The spines are venomous and give a painful sting, though not a dangerous one. Wild animals host commensal shrimp such as Periclimenes hirsutus, zebra crabs and juvenile cardinalfish among the spines.

In the wild

The blue spot urchin lives on sand, shingle and coral rubble in lagoons and sheltered bays across the Indo-Pacific. It ranges from East Africa to Hawaii and Australia, usually at 10 to 30 m. It hides by day and wanders open bottom at night, and in some places it gathers in dense herds.

Common questions

What size tank does a blue spot urchin need?

A blue spot urchin needs at least 100 gal (380 L). It spends most of its time in the bottom.

What temperature and pH does a blue spot urchin need?

A blue spot urchin is comfortable at 72–82°F (22–28°C) with a pH of 8.1–8.4.

What does a blue spot urchin eat?

A blue spot urchin grazes mainly on algae, but it also eats sponges, bivalves, small snails and dead animals. Feed it dried seaweed or algae pellets several times a week.

How big does a blue spot urchin get?

An adult blue spot urchin reaches about 7.9 in (20 cm).

Related species