Diadema setosum

Habitat & Distribution :  Coral reef, sandy flats and seagrass beds, Indo-Pacific Ocean

Diet : Algae

Size: 8 - 10 cm

Lifespan: 3 tahun

Description

The longspined black sea urchin has a round, ball-like body with a hard, calcareous test, black in coloration with five distinctive white spots. Its mouth is located at the bottom, ready to graze on any algae it passes, while the anus is situated on top. Yes. that's right, the colorful cone-like structure you see there is not its eye, but its anal cone!  It has long, thin, brittle, needle-like, black spines.

Behavior

The sea urchin is known to associate with coral reefs, but can also be found on sandy flats and seagrass beds. It has an important role as a grazer, able to consume a wide variety of algae in coral reefs, helping to limit its population and consequently, maintain ecological balance. 

When threatened, it can use its tube feet and long spines to make its quick escape. The long, sharp spines are also venomous and can be aimed toward the threat as a form of defensive warning and deterrent.

Reproduction

They are broadcast spawners. Gametes are released into the water by both sexes, and fertilization occurs externally. In subtropical and temperate regions, spawning has been observed to occur when temperature exceeds 25°C, while in tropical regions it occurs any other time. They have also been observed spawning on full moons.

Communication & Perception

When a sea urchin is injured or dies, it releases a chemical signal to warn other urchins of the presence of a predator or other dangers. The other urchins can "smell" this chemical through their tube feet and quickly make their escape. They can also sense light (i.e. "see") that is absorbed in their spines.

The sea urchin has also been observed using physical contact with each other to communicate, especially in the presence of food, helping to keep their population stable in places with abundance of algae.

Predator(s)

Sharks, sea otters, sea stars, wolf eels (Anarrhichthys ocellatus), triggerfish, and humans

Conservation Status : Least Concern (IUCN Red List; 2021)