Strongylocentrotus droebachiensis

Geographic Range

Strongylocentrotus droebachiensis inhabits colder temperatures of mostly northern oceans. Green sea urchins are found in coastal areas of Alaska to Washington, the western part of the Baltic Sea, on the coast of Korea, as well as in almost every other type of major marine habitats. (Hubbell, 1999; Smith, 2000)


Green sea urchins live primarily in areas with cold waters mainly in the northern hemisphere. Green sea urchins prefer living in rocky, or gravel areas, but they are mostly found in sandy, sea floor bottoms. Adults live in cold climates in water temperatures from 0 to 15 degrees Celsius. Green sea urchins are found between intertidal zones to about 1200 meters. The rate at which urchins take in or remove oxygen does not depend on water temperature.

The green sea urchin is one of the only urchins that has expanded into an environment of brackish water such as the Baltic Sea. (Banister and Campbell, 1985; Grzimek, 1972; Roessler, 1977; Smith, 2000)

  • Average depth
    1200 m
    3937.01 ft

Physical Description

Strongylocentrotus droebachiensis acquire their common name, "green sea urchin" from the green outer shell. All sea urchins have an exoskeleton made of calcitic plates rooted into their skin. The solid exoskeleton, or the test, is composed of several plates that are tightly bound together. The mouth is located in the center of the peristomial membrane. This membrane is composed of a flexible collogenous skin that is tough and serves as a type of lip-like structure. Teeth are found in the mouth to help tear off food to eat. Another structure that is commonly found with almost all sea urchins is the pedicellaria, tiny stalked valves used to keep the surface of the sea urchin clean by removing small particles it encounters. Sea urchins have spines and tubes that serve roles in acquiring food, protection and respiration. The tube-feet on the sea urchins are a type of suction discs that allow them to adhere onto other organisms or substances. They have also have an internal skeleton called the stereom.

Green sea urchins are very small, compact animals that usually do not exceed a length of 8 cm. The average size for a green sea urchin is about 7.8 cm. The larval forms are bilaterally symmetric. After metamorphosis they measure about 0.5 mm and are radially symmetric. The sexes are monomorphic. (Banister and Campbell, 1985; Grzimek, 1972; Smith, 2000; Thurman and Webber, 1984)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    0.5 to 80 mm
    0.02 to 3.15 in


Sexes of S. droebachiensis are separate, but monomorphic (similar in appearance). Green sea urchins, take several years to reach a point where they are sexually mature and capable of reproducing. For reproduction to occur there must be a large number of individuals. Reproduction occurs when both sperm and eggs are released simultaneously into the water column by both male and female urchins. There are about 100,000 to about 200,000 eggs released by female urchins. When these eggs are fertilized, they quickly form swimming larva known as echinopluteus, which feed off plankton. Then, slowly they mature into adult sea urchins. Urchins are about 0.5 mm after metamorphosis. (Hubbell, 1999; Smith, 2000)


Because they are such small animals, green sea urchins are vulnerable to predators. The spines that are located around its outer skeleton help protect them from predators such as lobsters, crabs, flatfish, wolffish, sea gulls, and others. The urchins also help protect other animals, such as small fish, from their predators by allowing these animals to seek shelter between their spines.

Strongylocentrotus droebachiensis usually come out at night to seek food. The green sea urchins hide until sunset and then search the area for food, mainly algae and kelp. If by chance light does hit these urchins, they begin to pulse sending out brilliant reds and blues until the light has been taken away from them.

Generally, the process of movement among sea urchins is by using their spines, which have muscles attached to it as well as a ball and socket joint. Sea urchins are not only able to move across sea grounds, but they can also climb rocks using their tube-feet. The tube-feet are also used for gas exchange. (Banister and Campbell, 1985; Grzimek, 1972; Roessler, 1977; Smith, 2000)

Food Habits

Green sea urchins feed on a wide variety of organisms, ranging from marine worms to sponges. However, this specific urchin particularly feed on a type of kelp known as Laminaria. Green sea urchins also eat bull kelp and green algae. Often, green sea urchins scrape the surface of rocks using their "Aristotle's lantern," or masticatory apparatus, in search of diatoms as well as algae. Whenever an urchin is injured, the other urchins immediately move away, but they return within a short time span to eat it. (Friedrich, 1969; Grzimek, 1972; Hubbell, 1999; Smith, 2000; Valiela, 1995)

Economic Importance for Humans: Positive

This species is harvested for its roe, which is considered a delicacy in Japan.

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of green sea urchins on humans.

Conservation Status

At this point, the green sea urchins and its habitat are not in any way threatened by the environment.

However, if green sea urchins were to be reduced in population, there would be mass amounts of kelp that would cause the water to be congested. This congestion does not allow boats to pass through the water. Therefore, it is important to preserve populations of this species. (Valiela, 1995)


Renee Sherman Mulcrone (editor).

Dubelza Buitron (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.


Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


A substance that provides both nutrients and energy to a living thing.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


seaweed. Algae that are large and photosynthetic.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


an animal that mainly eats all kinds of things, including plants and animals


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.


Alaska Fisheries Science Center, National Marine Fisheries Service, , National Oceanic and Atmospheric Association. "Green Urchin, Strongylocentrotus droebachiensis" (On-line). Accessed September 04, 2003 at

Banister, D., D. Campbell. 1985. The Encyclopedia of Aquatic Life. New York, N.Y.: Facts on File.

Friedrich, H. 1969. Marine Biology. United States: University of Washington Press.

Grzimek, B. 1972. Grzimek's Animal Life Encyclopedia: Volume 3- Mollusks and Echinoderms. New York: Van Nostand Reinhold Company.

Hubbell, S. 1999. Waiting for Aphrodite. New York: Houghton Mifflin Company.

Roessler, C. 1977. Underwater Wilderness. New York: Chanticleer Press.

Russel, D. "Strongylocentrotus droebachiensis. Northern sea urchin" (On-line). Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme, Plymouth: Marine Biological Association of the United Kingdom. Accessed July 15, 2004 at

Smith, A. 2000. "The Natural History Museum: The Echinoids" (On-line). Accessed May 20, 2003 at

Thurman, H., H. Webber. 1984. Marine Biology. Columbus, Ohio: Charles E. Merrill Publishing Company.

Tjärnö Marine Biological Laboratory, 2000. "Strongylocentrotus droebachiensis" (On-line). Aquascope. Accessed September 04, 2003 at

Valiela, I. 1995. Marine Ecological Processes. New York: Springer-Verlag New York, Inc..