It lives in shallow waters from the low-tide line to greater than 280 m (920 ft) deep,[2] and is typically found on rocky shores sheltered from extreme wave action in areas where kelp is available.

This bilaterally symmetrical larva, called an echinopluteus, subsequently develops a type of pentaradiate symmetry that characterizes echinoderms.

Scattered among its spines are rows of tiny tube feet with suckers that help it to move and stick to the sea floor.

[11] Red sea urchins are notoriously ravenous kelp-eaters and are implicated in devastating kelp beds[4] by forming grazing fronts.

[12] In contrast to their negatively perceived impact on community structure in open coastal kelp beds, the sedentary behavior and capture of detrital seaweed in the San Juan Islands is hypothesized to create an important habitat and energy source below the photic zone.

Eggs are fertilized externally while they float in the ocean, and planktonic larvae remain in the water column for about a month before settling on the bottom of the sea floor, where they undergo metamorphosis into juvenile urchins.