Animal Diversity Web

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)

• Biogeographic Regions
• arctic ocean
  • native
• atlantic ocean
  • native
• pacific ocean
  • native

Habitat

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)

• Habitat Regions
• saltwater or marine

• Aquatic Biomes
• benthic
• coastal

• Other Habitat Features
• intertidal or littoral

• 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)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry
• radial symmetry

• Sexual Dimorphism
• sexes alike

• Range length

  0.5 to 80 mm

  0.02 to 3.15 in

Reproduction

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)

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• fertilization
  • external
• oviparous

Behavior

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)

• Key Behaviors
• nocturnal
• motile

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)

• Primary Diet
• omnivore

• Plant Foods
• algae
• macroalgae

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)

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Contributors

Renee Sherman Mulcrone (editor).

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

References

Alaska Fisheries Science Center, National Marine Fisheries Service, , National Oceanic and Atmospheric Association. "Green Urchin, Strongylocentrotus droebachiensis" (On-line). Accessed September 04, 2003 at http://www.afsc.noaa.gov/kodiak/photo/misgrurch.htm.

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 http://www.marlin.ac.uk/species/Strdro.htm.

Smith, A. 2000. "The Natural History Museum: The Echinoids" (On-line). Accessed May 20, 2003 at http://www.nhm.ac.uk/palaeontology/echinoids/index.html.

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 http://www.vattenkikaren.gu.se/fakta/arter/echinode/echinoid/strodroe/strodre.html.

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