Common Sea Urchin

The common sea urchin is a robust, dome-shaped echinoid found across rocky reefs and kelp forests from shallow subtidal zones down to about 100 metres. Its purple or reddish test is covered in blunt spines and typically reaches 8–10 cm in diameter. A grazer on algae and kelp, it congregates in crevices and under rock overhangs, emerging at night to feed. Divers often spot them in dense aggregations on suitable substrate, where they slowly consume the seaweed that carpets the reef.