Alaska Species Explorer

Green Sea Urchin

Common Name: Green Sea Urchin
Scientific Name: Strongylocentrotus droebachiensis
Size: Up to 9cm (3.6in) across, average around 5cm (2in)

Northern hemisphere, including some Arctic waters; in the Pacific south to northern Washington. 


Rocky intertidal up to 1,150m (3,770 ft), most common from intertidal to 9m (30 ft)

Life History:

Sea urchins have separate male and female individuals.  They may use an environmental cue such as temperature or daylight hours to synchronize the release of their gametes into open water during spawning.  Larval sea urchins pass through different planktonic stages before settling out of the water column to feed on the ocean floor.  They grow larger by expanding the number and size of the hard calcite plates of their test.

Diet in the Wild:

Kelp and other algae, occasionally scavenge on fish and invertebrates.  Sea urchins use their 5 radially arranged teeth to scrape and tear. 

Natural Predators: Seastars, crabs, wolf eels and other large fish, sea otters
Population Status:

Green and red sea urchins are the only commercially harvested urchins in Alaska. They are harvested for their eggs which are considered a delicacy in many cultures.  Green sea urchins are currently harvested by divers in a small area around Kodiak Island.  A smaller commercial fishery that once existed in southeast Alaska was not sustainable.  Ocean acidification is expected to have a detrimental effect on the growth of echinoderm skeletons, including the tests of sea urchin.

Additional Information:

A sea urchin has 3 distinctive structures extending from its hard body wall or test: spines, tube feet and pedicellaria.  Green sea urchin spines provide protection although they are not venomous.  Tube feet are controlled by a water vascular system and are used for locomotion, food collection and holding onto small rocks and shells used for camouflage.  Pedicellaria are thin, flexible stalks topped by a small claw-like structure that assist in food capture, protection and keeping the surface of the urchin clean of parasistes and debris. 

Fun Facts:
  • Aristotle’s lantern is the name given to the unique mouth structure of sea urchins.  Their teeth are so strong and sharp that they can scratch and damage their aquarium habitats as they graze on the algae growing on the acrylic windows.
  • Dry sea urchin tests are covered with hundreds of bead-like bumps.  These are the pivot points on which the spines move.