TankBud

Purple urchin

Arbacia punctulata

Also known as Atlantic Purple Sea Urchin, Purple-spined Sea Urchin

SaltwaterInvertebrate

Purple urchin (Arbacia punctulata)
NOAA · Public domain

Care at a glance

Temperature
68–81°F
20–27°C
pH
8.1–8.4
Adult size
3.1 in
8 cm
Minimum tank
20 gal
75 L
Temperament
Peaceful
Social behavior
Solitary
Swim level
Bottom
Diet
Omnivore
Difficulty
Easy
Breeding
Hard
Rarity
Common
Reef safe
Reef safe with caution
Family
Arbaciidae
Origin
Western Atlantic, from New England to the Caribbean and Gulf of Mexico

Overview

The purple urchin is a hardy, bottom-dwelling algae grazer for a saltwater tank. It is easy to keep, though it is reef safe only with caution.

Did you know

The purple urchin has been a workhorse of biology labs for over a century. Classic discoveries about fertilization and cell division were made using its eggs.

Caring for the purple urchin

Keep a purple urchin in at least 20 gal (75 L), with sturdy, well-stacked rockwork. It shoulders straight through anything loosely placed.

Hold the water at 68 to 81°F (20 to 27°C) and a pH of 8.1 to 8.4. The purple urchin is a tireless grazer that strips nuisance algae. Feed nori once the natural algae is gone.

Unlike most cleanup crew urchins, it is a true omnivore and does not stop at algae. It rasps away coralline, bulldozes or carries off loose frags, and will also eat sponges, bryozoans and other sessile animals. That makes it best for fish-only systems and rough-and-ready reef tanks, where its appetite is an asset rather than a risk. Breeding it is hard.

Good to know

The purple urchin, Arbacia punctulata, is a dark, purple-spined urchin in the family Arbaciidae. It is also sold as the Atlantic purple sea urchin or the purple-spined sea urchin.

In the wild

The purple urchin is native to the western Atlantic, from New England down to the Caribbean and the Gulf of Mexico. It lives on shallow rocky, sandy and shelly bottoms.

Common questions

What size tank does a purple urchin need?

A purple urchin needs at least 20 gal (75 L). It spends most of its time in the bottom.

What temperature and pH does a purple urchin need?

A purple urchin is comfortable at 68–81°F (20–27°C) with a pH of 8.1–8.4.

What does a purple urchin eat?

A purple urchin grazes algae, including nuisance algae and coralline. It also eats sponges, bryozoans and other sessile animals, and it needs nori once the natural algae is gone.

How big does a purple urchin get?

An adult purple urchin reaches about 3.1 in (8 cm).

Related species