TankBud

Caribbean long-spined urchin

Diadema antillarum

Also known as Long-spined black urchin, Lime urchin

SaltwaterInvertebrate

Caribbean long-spined urchin (Diadema antillarum)
NOAA · Public domain

Care at a glance

Temperature
72–81°F
22–27°C
pH
8.1–8.4
Adult size
3.9 in
10 cm
Minimum tank
79 gal
300 L
Temperament
Peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Difficulty
Easy
Breeding
Hard
Rarity
Rare
Reef safe
Reef safe with caution
Family
Diadematidae
Origin
Tropical western Atlantic reefs, Florida and the Caribbean to Brazil

Overview

The Caribbean long-spined urchin is a peaceful, nocturnal urchin and one of the best algae grazers there is. It is easy to keep in a large tank.

Did you know

Before 1983, the Caribbean long-spined urchin was the main lawnmower of Caribbean reefs. A waterborne disease killed more than 95 percent of them in about a year, and algae smothered coral across the whole region. Hatcheries in Florida, Puerto Rico and Jamaica now rear larvae and plant juveniles back on reefs to try to reverse it.

Caring for the Caribbean long-spined urchin

Give the Caribbean long-spined urchin solid, well-spaced rock with caves that fit a spine span of 60 cm. Leave out sharp overhangs that could snap its spines. It needs a tank of at least 79 gal (300 L).

Keep the water at 72 to 81°F (22 to 27°C) with a pH of 8.1 to 8.4. Hold calcium and alkalinity steady so the spines regrow, and never use copper. Spine loss means poor water. Drip acclimate it slowly.

It grazes turf, hair algae and coralline alike. Feed it dried seaweed when the rock is clean.

A hungry one grazes zoanthids and young coral, so treat it as a reef caution. Its long, brittle spines are also a hazard to you and to slow fish. Triggers, puffers and large wrasses will eat it.

Good to know

Diadema antillarum is a diadematid urchin. The test is black, with the iridescent blue lines the genus shares. It lacks the orange ring around the anal cone that marks the Indo-Pacific D. setosum. The hollow, needle-sharp spines run 10 to 12 cm in most animals and up to 30 cm in big ones. They are mildly venomous and break off in skin like a bee sting that lingers. Juveniles have black and white banded spines, and the odd adult is white. Its numbers had barely begun to recover from the die-off of 1983 and 1984 when a second one started in 2022. That one was traced to a ciliate, Philaster apodigitiformis. Most trade listings for black long-spine urchins are the Indo-Pacific Diadema setosum, not this species. Florida prohibits any harvest or sale of D. antillarum, so true Caribbean stock is scarce.

In the wild

The Caribbean long-spined urchin lives on coral reefs, hard bottom, seagrass beds and mangrove roots throughout the tropical western Atlantic. It ranges from Florida and Bermuda through the Caribbean to Brazil, mostly at 1 to 10 m. It spends the day wedged in a crevice and grazes within about a meter of home at night.

Common questions

What size tank does a Caribbean long-spined urchin need?

A Caribbean long-spined urchin needs at least 79 gal (300 L). It spends most of its time in the bottom.

What temperature and pH does a Caribbean long-spined urchin need?

A Caribbean long-spined urchin is comfortable at 72–81°F (22–27°C) with a pH of 8.1–8.4.

What does a Caribbean long-spined urchin eat?

A Caribbean long-spined urchin grazes turf, hair algae and coralline alike, and it takes dried seaweed when the rock is clean. A hungry one also grazes zoanthids and young coral.

How big does a Caribbean long-spined urchin get?

An adult Caribbean long-spined urchin reaches about 3.9 in (10 cm).

Related species