Green Sea Urchin Facts

Sea Urchins / Jennifer Kennedy
Green sea urchins, showing tube feet and "Aristotle's lantern" (mouth). Taken at the Seacoast Science Center in Rye, NH. © Jennifer Kennedy, Licensed to About.com

With its sharp-looking spines, the green sea urchin may look frightful, but to us it is mostly harmless. Sea urchins aren't poisonous, although you might get poked by a spine if you're not careful. In fact, green sea urchins can even be eaten. Here you can learn some facts about this common marine invertebrate.

Sea Urchin Identification

Green sea urchins can grow to about 3" across, and 1.5" high. They are covered in thin, short spines.

The sea urchin's mouth (called the Aristotle's lantern) is located on its underside, and its anus is on its top side, in a spot that is not covered with spines. Despite their immobile appearance, sea urchins can move relatively quickly, like a sea star, using their long, thin water-filled tube feet and suction.

Where to Find Sea Urchins:

If you're tide pooling, you might find sea urchins underneath rocks. Look closely - sea urchins may camouflage themselves by attaching algae, rocks and detritus to their spines.

Classification:

  • Kingdom: Animalia
  • Phylum: Echinodermata
  • Class: Echinoidea
  • Order: Camarodonta
  • Family: Strongylocentrotidae
  • Genus: Stronglyocentrotus
  • Species: droebachiensis

Feeding:

Sea urchins feed on algae, scraping it off of rocks with their mouth, which is made up of 5 teeth collectively called the Aristotle's lantern. In addition to his work and writings on philosophy, Aristotle wrote about science, and sea urchins - he described the sea urchin's teeth by saying they resembled a lantern made of horn that had 5 sides (more on this here).

Thus the urchin's teeth came to be known as Aristotle's lantern.

Habitat and Distribution:

Green sea urchins are found in tide pools, kelp beds, and on rocky ocean bottoms, to areas as deep as 3,800 feet.

Reproduction:

Green sea urchins have separate sexes, although it is difficult to tell males and females apart.

They reproduce by releasing gametes (sperm and eggs) into the water, where fertilization takes place. A larva forms and lives in the plankton for up to several months before it settles on the sea floor and eventually turns into an adult form.

Conservation and Human Uses:

Sea urchin roe (eggs), called uni in Japan, are considered a delicacy. Maine fishermen became huge suppliers of green sea urchins in the 1980's and 1990's, when the ability to fly urchins overnight to Japan opened an international market for urchins, creating a "Green Gold Rush", in which millions of pounds of urchins were harvested for their roe. Overharvesting amid a lack of regulation caused the urchin population to bust.

Regulations now prevent overharvesting of urchins, but populations have been slow to recover. The lack of grazing urchins has caused kelp and algae beds to flourish, which in turn has increased crab populations. Crabs love to eat baby urchins, which has contributed to the lack of recovery of urchin populations.

Sources:

  • Ganong, Rachel. 2009. Return of the Urchin?(Online). Times Record. Accessed June 14, 2011 - no longer online as of 5/1/12.
  • Kiley Mack, Sharon. 2009. Maine Sea Urchins Making a Slow Recovery (Online) Bangor Daily News. Accessed June 14, 2011.
  • Maine Department of Marine Resources. Green Sea Urchins (Strongylocentrotus drobachiensis) in Maine - Fishery, Monitoring, and Research Information. (Online) Maine DMR. Accessed June 14, 2011.
  • Martinez, Andrew J. 2003. Marine Life of the North Atlantic. Aqua Quest Publications, Inc.: New York.
  • Meinkoth, N.A. 1981. National Audubon Society Field Guide to North American Seashore Creatures. Alfred A. Knopf, New York.