Pacific Purple Sea Urchin

Overview

The Pacific Purple Sea Urchin is a prominent marine echinoderm recognized by its vibrant purple coloration and spherical, spine-covered body. Native to the northeastern Pacific, this species plays a critical ecological role as a primary grazer in rocky intertidal and shallow subtidal communities. It is also widely utilized as a model organism in scientific research due to its well-studied genome and life history.

Distribution & habitat

This species is found along the eastern Pacific coastline, ranging from Alaska to Cedros Island, Mexico. It thrives in areas with moderate to strong wave action and well-aerated water, typically inhabiting the low intertidal and shallow subtidal zones. These urchins are often found in rocky crevices or within pits they erode into the bedrock using their spines and teeth.

Appearance

Adults are characterized by a radially symmetrical test (shell) covered in long, deep purple spines. Juveniles are generally smaller and often display a pale green hue. The body also features tube feet for locomotion and pincer-like organs called pedicellariae used for defense and cleaning.

Biology & behavior

Pacific Purple Sea Urchins are mobile but often remain sedentary in protective pits or crevices. To defend against predators like sea stars, they may lower their spines and deploy their pedicellariae. They are known to hold debris, such as rocks or algae, over their bodies using their tube feet for camouflage or protection.

Feeding

As primary grazers, they feed mainly on macroalgae, with giant kelp being a preferred food source. When kelp is scarce, they may shift to consuming other algae, chitons, or organic detritus. They use a specialized mouthpart known as Aristotle's lantern to scrape food from the substrate.

Reproduction

Reproduction is sexual and seasonal, with spawning typically peaking between January and March. Males and females release gametes into the water column, where external fertilization occurs. The resulting larvae are planktonic before settling to the substrate to metamorphose into juveniles, reaching sexual maturity at approximately two years of age.