|Description: Body up 12cm across, spines up to 8cm. They can be red , red brown or light to dark purple
Usually, they eat red or brown algae (see in the photograph they have eaten pieces of the kelp Nereocystis), periwinkles, and occasionally barnacles or mussels.
Distribution; rocky areas though at exposed and protected coastal waters.
Habitat: Rocky substrates, especially ledges and crevices located near bull kelp beds and other brown algae in area of moderate to swift currents. Larvae drift and feed in plankton, juveniles settle near kelp bed, often associate with aggregation of adults, remain under adult spines until they reach 40mm.
Behavior: The red sea urchin is found in deeper water than the purple sea urchin. It is seen from the low intertidal area to as deep as 90 meters. The urchins move their feet by a hydraulic system which creates suction in the end of the food by pulling water out the madroporite. These tube feet may also be used to sense of smell the chemicals in their surroundings like others urchins, the red sea urchin can regrow its spines if they are broken. On full size urchins, these spines sometimes shelter small juveniles.
Reproduction: The spawning of red sea urchin peaks between, June and September in southern BC. The fertilized eggs develop into planktonic larvae before settling on the bottom where they change into tiny juvenile sea urchins. This replenishment of the population, appears to occur annually in local waters. New recruits must hide from potential predators and many seek shelter under the spines of adult . Adulthood is at approx. 3cm diameter and legal size of 10cm is reached in five to ten years. Life span sometimes exceeds 30 years.
People eat the gonads (sexual organs, called "UNI") of this urchin. It is especially a delicacy in Japan and others parts of Asia. Sunflower stars, some fish, birds, and sea otters also prey on them.