Pacific Purple Sea Urchin

Strongylocentrotus purpuratus

Range: Pacific Ocean - Alaska to Baja California

Named for their iconic bright purple color, Pacific purple sea urchins can be found all over the mid to low rocky intertidal zones and kelp forests of the Eastern Pacific. Due to local declines in the populations of their primary predators - including the sunflower star (Pycnopodia helianthoides) and, historically, the sea otter (Enhydra lutris) - this species has become concerningly overpopulated along eastern Pacific coasts (especially in California). These incredibly populous, voracious herbivores have become infamous for decimating once-thriving and extensive California kelp forest ecosystems, leaving behind vast, desolate stretches of urchin barrens in their wake.

Kasitsna Bay Laboratory, Seldovia, AK (June 2025)

Spot the Difference: Juvenile Green and Purple Urchins!

Even though only green urchins (Strongylocentrotus droebachiensis) are green in adulthood, both green urchins and purple urchins (S. purpuratus) are green as juveniles! So how can you tell them apart when they're young? In the image on the left, the upper left urchin is a true juvenile green urchin, and the lower right urchin is a juvenile purple urchin. You can tell them apart by the length of their spines relative to the test, with the purple urchin having relatively longer (and often thinner) spines than the green urchin.