Diadema Sea Urchin

(Diadema sp.)


Diadema Sea Urchin IUCN NOT EVALUATED (NE)


Facts about this animal

There are 7 species in the genus Diadema which are mainly separated geographically but less morphologically viz. D. antillarum, D. ascensionis, D. mexicanum, D. palmieri, D. paucispinum, D. savigny and D. setosum. D. savignyi and D. setosum are known to hybridize.

The test of the Diadema Sea Urchin is similar to other sea urchins but the black spines are exceptionally long and slender. They are usually 10-12 cm long but can reach 30 cm. The hollow spines are slightly poisonous. The up to 9 cm large test is black but may have white, blue and orange spots.

Diadema Sea Urchins hide by day in a sheltered crevice and leave it to graze by night about 1 m around their crevice on algae and seagrass. Hungry specimens may become carnivorous. They will also bite bits of the rocks and probably ill corals as well and as a result will produce coral sand which humans like on a tropical beach.

Diadema Sea Urchins need high densities to reproduce because males and females stimulate the opposite sex chemically to spawn what fails at low densities - in D. setosum spawning is thought to be induces by lunar phases. A female produces 10-20 million eggs at each spawning. The larvae will live 40-50 day in the plankton and are an important food source because of their great number. For settling and metamorphosis they need naked rock cleaned by adults. To live below the adults’ spines will protect them of enemies.

Diadema Sea Urchins are numerous, widespread, and of great ecological importance. This became obvious when in 1983 more than 97 % of the formerly common Caribbean species D. antillarum, also called Long-spined Sea Urchin, died of unknown reasons – maybe 2 species of bacteria were responsible (Clostridium perfringens and C. sordelli). Within short time macro-algae, which formerly were kept very short by D. antillarum, developed well and overgrew the reef corals. Subsequently the corals died by lack of sun light for their symbiotic micro-algae (70 % coral cover in the decades before compared to presently less than 10 %). The macro-algae also passively collected sediments and the reefs were complete changed. Many other inhabitants of the reefs did no longer find enough shelter or food and were consumed by larger predators – the complete ecosystem collapsed – the greatest marine catastrophe ever recorded in human history. D. antillarum has not yet recovered because of difficulties to reproduce and humans try to help the species with transfer programs to aggregate the scattered specimens, artificial reefs and breeding in captivity which is quite difficult. There are economical consequences, too, since tourists which formerly enjoyed the amazing reefs fail to come.

Where still abundant Diadema Sea Urchins may harm careless scuba or lobster divers.

Did you know?
that Diadema Sea Urchins are key factor species of tropical coral reefs without which the complete biocoenosis will collapse within months? that the spines of the sea urchins are covered with skin except at the extreme tip which can break off if touched to release a weak poison? That the spines of the sea urchins are not fix but have a basal articulation and can be moved or fixed with surrounding muscles?


Name (Scientific) Diadema sp.
Name (English) Diadema Sea Urchin
Name (French) Oursin diadème, Oursin à longs piquants
Name (German) Diademseeigel
Name (Spanish) Erizo negro
CITES Status Not listed
CMS Status Not listed



Photo Copyright by
Vladimír Motyčka



Range All in tropical seas, especially in the Indo-Pacific Ocean, e.g. D. antillarum in the Caribbean Sea, D. palmieri in the South-western Pacific Ocean, D. setosum in the Red Sea and the Indo-Pacific Ocean.
Habitat In tropical shallow waters down to 70 m (rarely 200 m) depth. Usually only 1-10 m deep.
Wild population Usually very abundant with 2-20 specimens per square meter, but D. antillarum became very rare in 1983 and has not yet recovered.
Zoo population 220 reported to ISIS (2008) (47 undetermined, 39 D. antillarum, 3 D. mexicanum, 131 D. setosum)

In the Zoo

Diadema Sea Urchin


How this animal should be transported

As a rule for any species of sea Urchins Diadema Sea Urchins should not come into contact with air since air bubbles may be kept between the spines what make them float.


Find this animal on ZooLex


Photo Copyright by
Vladimír Motyčka

Why do zoos keep this animal

Diadema Sea Urchins are kept for educational reasons to demonstrate the ecological importance of this herbivore on the vitality of a tropical coral reef.