Blue-spotted Urchin

Overview

The Blue-spotted Urchin (Astropyga radiata) is a striking, large sea urchin widely distributed across the tropical Indo-Pacific region. It is easily recognized by its vibrant coloration and distinct patterns, often found inhabiting coral reefs, lagoons, and sandy or rubble-strewn sea floors.

Appearance

This species features a globular, slightly flattened test that can reach up to 20 cm in diameter. Its body is typically a deep red, purple, or brownish-red, marked by five prominent, V-shaped bare zones that radiate from the center, resembling a five-pointed star or Maltese cross. These areas are lined with rows of luminous, iridescent blue spots. The urchin possesses long, slender spines, which may be banded in juveniles, and a visible, often light-colored anal papilla on its upper surface.

Biology & Behavior

Primarily nocturnal, the Blue-spotted Urchin remains hidden in crevices, rubble, or seagrass beds during the day to avoid predators. It emerges at night to forage across the substrate. While generally peaceful, it possesses sharp, venomous spines that can deliver a painful sting if handled, serving as an effective defense mechanism. It is often found living solitarily or in loose groups and may occasionally act as a host for small fish or crustaceans seeking shelter among its spines.

Feeding

As an omnivore, this urchin plays an active role in its ecosystem by grazing on algae, biofilm, and organic detritus. It may also consume small invertebrates, sponges, and other organic matter found on the reef surface.