Long Spine Sea Urchin Care Guide
Diadema setosum is an Indo-Pacific urchin with very long, mildly venomous black spines. It is an effective algae grazer for large reef tanks.
Compiled by Aquairi from published sources · Published · Updated
Overview
Diadema setosum, the long-spine sea urchin, is an echinoid of the family Diadematidae from the Indo-Pacific. Its spines are extremely long and narrow in proportion to the body, hollow, and carry a mild venom; the test is black and marked by five white spots, with a bright orange ring around the periproctal cone. It is a prolific algae grazer and a useful, if hazardous, cleanup animal in large reef systems.
Taxonomy
- Class: Echinoidea
- Order: Diadematoida
- Family: Diadematidae
- Genus: Diadema
- Scientific name: Diadema setosum (Leske, 1778)
Habitat
The species ranges throughout the Indo-Pacific basin, from the Red Sea eastward to Australia, north to Japan and south to the east coast of Africa. It occupies coral reefs, sand flats and seagrass beds, where it can reach high local densities. Adults measure about 70 mm in test diameter and 40 mm in height.
Tank requirements
- Minimum tank volume: 200 L
- Temperature: 24–26 °C (75–79 °F)
- pH: 8.1–8.4
- Carbonate hardness (dKH): 8–11
- Specific gravity: 1.024–1.026
- Adult diameter including spines: large; allow ample open rockwork
- Lifespan: roughly 4–10 years
A large tank with abundant live rock and stable parameters suits this urchin; if grazeable algae runs low, offer dried algae sheets so it does not starve and turn to scraping coralline or coral.
Diet
Diadema setosum is a herbivore that grazes a wide variety of algae common on tropical reefs, including nuisance hair algae. It is largely nocturnal, hiding by day and emerging at night to forage.
Compatibility
It is generally considered reef compatible as an algae grazer, but its long, sharp spines can knock or abrade nearby corals, so it needs space. Avoid housing it with known urchin predators such as triggerfish and pufferfish.
Diadema setosum Breeding Guide: Long-Spine Urchin Spawning
Overview
Diadema setosum is a long-spined sea urchin in the family Diadematidae, class Echinoidea, and one of the oldest known living members of its genus. It ranges across the Indo-Pacific from the Red Sea eastward to Australia, north to Japan and south along East Africa, and has been recorded as invasive in the Mediterranean off Turkey. Its very long, hollow spines carry mild venom; it is an effective grazer of tropical reef algae.
Reproductive Mode
The species is a broadcast spawner with temperature-dependent timing. Temperatures above 25 °C have been cited as a possible spawning cue, equatorial populations spawn year-round, Persian Gulf populations spawn around April to May, and full-moon phases also influence spawning.
Sexual Reproduction
As a free-spawning echinoid, males and females release gametes into the water, where fertilisation occurs externally and the embryos develop into planktonic larvae that drift before settling and metamorphosing into juveniles. This dispersal-dependent larval phase is the only reproductive route in this species.
Common Challenges
The planktonic larval cycle cannot be completed in home aquaria, which lack the open-water dispersal and larval microfood it requires. Sea urchins do not reproduce asexually, so there is no fragmentation route either. The long, brittle spines are mildly venomous and demand caution during maintenance.