Indo-pacific Rock-boring Urchin

Overview

The Indo-Pacific Rock-boring Urchin is a highly abundant sea urchin widely distributed across tropical and subtropical reefs in the Indo-Pacific region. It is well-known for its specialized behavior of excavating and inhabiting cavities within hard, rocky substrates, which provides essential protection from wave action and predators.

Appearance

This species typically features an ovoid, dark-colored test that reaches approximately 5 cm in diameter. Its primary spines are relatively short, thick, and robust, often displaying variable colors such as green or purple with distinct purple tips. A key identifying feature is the presence of a characteristic pale or white ring at the base of each spine, which helps distinguish it from similar species.

Biology & behavior

As a dedicated rock-borer, this urchin uses its spines and specialized mouthparts, known as Aristotle's lantern, to actively grind into basaltic and calcareous rock. While it remains sheltered in these hollows during the day, it emerges at night to graze. Its burrowing activity contributes to the bioerosion of coral reefs, though it also enhances habitat rugosity. The species is gonochoristic, meaning individuals are either male or female, and it reproduces by releasing gametes into the water column for external fertilization.

Feeding

This urchin is primarily an herbivore that grazes on fleshy benthic algae. It may also consume other encrusting organisms, such as sponges, found on the reef surface.