Pacific purple urchin
Strongylocentrotus purpuratus
Also known as Purple sea urchin, California purple sea urchin, West Coast purple urchin
SaltwaterInvertebrate
Care at a glance
- Temperature
- 46–64°F
- 8–18°C
- pH
- 8.1–8.4
- Adult size
- 3.9 in
- 10 cm
- Minimum tank
- 53 gal
- 200 L
- Temperament
- Peaceful
- Social behavior
- Solitary
- Tankmates
- With caution
- Swim level
- Bottom
- Diet
- Herbivore
- Difficulty
- Difficult
- Breeding
- Hard
- Rarity
- Rare
- Reef safe
- Not reef safe
- Family
- Strongylocentrotidae
- Origin
- Eastern Pacific rocky shores, Alaska to Baja California
Overview
The Pacific purple urchin is a peaceful, very hungry grazer for a coldwater tank. It is hardy at the right temperature, but it is still an animal for experienced keepers.
Did you know
The Pacific purple urchin's genome, sequenced in 2006, was the first for any echinoderm. It carries about 23,500 genes and shares roughly 7,700 of them with people, including a surprisingly large set of immune genes. It is one of the oldest lab animals in biology, used to watch fertilization and cell division since the 1800s.
Caring for the Pacific purple urchin
Keep the Pacific purple urchin in a coldwater tank of at least 53 gal (200 L), with strong flow and rock to bore into. It needs a chiller in almost every home. Drip acclimate it, and never use copper.
Hold the water at 46 to 64°F (8 to 18°C) and a pH of 8.1 to 8.4, with lots of oxygen. Water warmer than about 23°C kills it, which rules out any tropical tank and is why it is not reef safe. Spine loss means the water is too warm or too dirty.
Feed it kelp, dried seaweed and algae pellets. In a coldwater tank it will strip every kelp blade or macroalga you put in.
It is peaceful and fine in groups of its own kind. Keep it with other cold Pacific tide pool animals, and add any tank mate with caution. Breeding it is hard.
Good to know
Strongylocentrotus purpuratus is a regular urchin in the family Strongylocentrotidae. Its test is usually 5 to 8 cm across, with short, deep purple spines, and juveniles start out greenish. It matures at about two years and may live 70 years or more. Do not confuse it with the catalog's purple urchin, Arbacia punctulata, which is a warm-water Atlantic species.
In the wild
The Pacific purple urchin lives on wave-washed rock in the low intertidal and shallow subtidal of the eastern Pacific. Its range runs from Alaska to Cedros Island in Baja California, in and around kelp forests. It grinds shallow pits into rock with its teeth and spines and often sits in one for life. In the wild it eats kelp, giant kelp above all. Where sea otters and sunflower stars are gone, purple urchin herds have mown whole kelp forests into urchin barrens.
Common questions
What size tank does a Pacific purple urchin need?
A Pacific purple urchin needs at least 53 gal (200 L). It spends most of its time in the bottom.
What temperature and pH does a Pacific purple urchin need?
A Pacific purple urchin is comfortable at 46–64°F (8–18°C) with a pH of 8.1–8.4.
What does a Pacific purple urchin eat?
A Pacific purple urchin eats kelp, dried seaweed and algae pellets. Any kelp or macroalgae you add to its tank will be stripped bare.
How big does a Pacific purple urchin get?
An adult Pacific purple urchin reaches about 3.9 in (10 cm).
Related species
- 3.5 in (9 cm)40 gal (150 L)36–59°F (2–15°C)
Green sea urchin
Strongylocentrotus droebachiensis
3.5 in (9 cm) · 40 gal (150 L)
2.8 in (7 cm)40 gal (150 L)54–75°F (12–24°C)Mediterranean purple urchin
Paracentrotus lividus
2.8 in (7 cm) · 40 gal (150 L)
3.9 in (10 cm)79 gal (300 L)72–81°F (22–27°C)Caribbean long-spined urchin
Diadema antillarum
3.9 in (10 cm) · 79 gal (300 L)
3.9 in (10 cm)11 gal (40 L)75–81°F (24–27°C)Social feather duster
Bispira brunnea
3.9 in (10 cm) · 11 gal (40 L)
3.9 in (10 cm)20 gal (75 L)72–81°F (22–27°C)White urchin
Lytechinus variegatus
3.9 in (10 cm) · 20 gal (75 L)
3.9 in (10 cm)11 gal (40 L)75–81°F (24–27°C)Yellow sea cucumber
Colochirus robustus
3.9 in (10 cm) · 11 gal (40 L)