TankBud

Green sea urchin

Strongylocentrotus droebachiensis

Also known as Northern green sea urchin, Green urchin

SaltwaterInvertebrate

Care at a glance

Temperature
36–59°F
2–15°C
pH
8.1–8.4
Adult size
3.5 in
9 cm
Minimum tank
40 gal
150 L
Temperament
Peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Omnivore
Difficulty
Difficult
Breeding
Hard
Rarity
Very rare
Reef safe
Not reef safe
Family
Strongylocentrotidae
Origin
Cold northern seas around the globe, Arctic to Maine, Britain and Puget Sound

Overview

The green sea urchin is a peaceful cold-water urchin for a chilled tank, and it is not a reef tank animal at all. It is a difficult animal for experienced keepers.

Did you know

The green sea urchin can be aged with a ruler. It grows about 10 mm of test a year, so a 5 cm animal is roughly five years old. The 8.7 cm record holder was nearly nine years old.

Caring for the green sea urchin

Give the green sea urchin at least 40 gal (150 L), with rock, strong oxygenated flow and dim light. In a chilled tank, it can clear every macroalga and kelp frond within reach.

It is the coldest-water urchin in this catalog and needs 36 to 59°F (2 to 15°C), so a chiller is not optional. A summer spike above about 20°C will kill it. Keep the water cold and high in oxygen, at a pH of 8.1 to 8.4.

It tolerates lower salinity than most urchins. Drip acclimate it, and never use copper. Feed it kelp, dried seaweed and algae wafers. It will also take small animals.

Keep it with other cold North Atlantic or North Pacific animals. Sea stars, crabs, lobsters and wolffish eat it in the wild, so choose tank mates with that in mind. Breeding it is hard.

Good to know

Strongylocentrotus droebachiensis is a regular urchin in the family Strongylocentrotidae. It is named for the town of Drobak on the Oslo Fjord, where Muller described it in 1776. It has a pale green test with short green spines. It supports a roe fishery in Maine, Canada, Norway and Russia, and it is farmed experimentally. The trade sometimes calls the tropical Lytechinus variegatus a green sea urchin, but that is a different animal that takes warm water.

In the wild

The green sea urchin lives on rocky bottom in cold northern water right around the globe. It ranges from the Arctic at 81 degrees north down to Maine and Cape Cod. Its range also takes in the British Isles, Norway, Puget Sound, Sakhalin and the Kuril Islands. It is found from the tide line to over 1,000 m. It grazes kelp beds and in places has eaten them down to bare rock.

Common questions

What size tank does a green sea urchin need?

A green sea urchin needs at least 40 gal (150 L). It spends most of its time in the bottom.

What temperature and pH does a green sea urchin need?

A green sea urchin is comfortable at 36–59°F (2–15°C) with a pH of 8.1–8.4.

What does a green sea urchin eat?

A green sea urchin eats kelp, dried seaweed and algae wafers in the tank. It will also take small animals.

How big does a green sea urchin get?

An adult green sea urchin reaches about 3.5 in (9 cm).

Related species