Strongylocentrotus franciscanus (A. Agassiz, 1863)

Common name(s): Red urchin, Giant red sea urchin

Phylum Echinodermata
 Class Echinoidea
  Subclass Euechinoidea
   Order Echinoida
    Family Strongylocentrotidae
Strongylocentrotus franciscanus collected from Sares Head, 15 m depth.  Total width approximately 20 cm.  Note the different colors of the two individuals.  The two smaller urchins below are S. droebachiensis and S. purpuratus.
(Photo by: Dave Cowles, August 1997)
Description:  This is the largest urchin found in the Pacific Northwest.  Color of spines varies--may be red, brick red, pink, purple, or even maroon.  Spines up to 7 cm long.  Up to 20 cm diameter (or more).  Test diameter up to 17 cm.  Tube feet are dark, often wine red.

How to Distinguish from Similar Species: Strongylocentrotus purpuratus is smaller and a strong purple color.  Small S. franciscanus can look very much like S. purpuratus but S. franciscanus has longer spines--nearly as long as the test is wide.  This species is common both on the open coast and protected waters, while S. purpuratus is found mostly on the open coast.

Geographical Range: Gulf of Alaska to Isla Cedros, Baja California; northern Japan

Depth Range: Low intertidal to 284 m; mostly subtidal.

Habitat: Rocky reefs, especially around kelp.

Biology/Natural History: Feed primarily on kelp (especially Nereocystis or Macrocystis) but can eat sessile invertebrates.  Often forms large subtidal aggregations in or near kelp beds.  A prime food for sea otters.  Other predators include the sunflower star Pycnopodia helianthoides, leather star Dermasterias imbricata, red rock crab Cancer productus, spiny lobster Panulirus interruptus and sheephead fish (in S California), and humans.  Commensals include the rhabdocoele flatworm Syndesmis (or Syndisyrinx) franciscanus, less than 1 cm long and lives inside the test, the isopod Colidotea restrata, which clings to the spines, and the amphipod Dulichia rhabdoplastis which builds rods of its fecal pellets that extend out from the urchin's spines (photo).  The amphipod feeds on diatoms, which it seems to "farm" on the spines.  Plots from which urchins were excluded became overgrown by large algae.  Small urchins (less than 5 cm test diameter) often hide under the adults.  In Puget Sound they spawn spring and summer.  Pelagic echinopluteus larvae metamorphose into benthic juveniles after about 6-10 weeks.  Young urchins often are found under larger individuals.  Nishizaki and Ackerman (see ref below) found that adult urchins release a chemical cue that causes the young to aggregate underneath them when the adults detect the presence of Pycnopodia helianthoides.  Ebert (1998) and Ebert and Southon (2003) determined that these urchins live over 100 years, and found some near Vancouver Island that may be 200 years old.  They seem to reproduce best when in dense aggregations (Ebert 1998).  Aggregations from which smaller individuals have been harvested recover much faster than those from which larger individuals have been removed (Rogers-Bennet et al., 1998).  At depths over 70 m in the Salish Sea area they aggregate on shallow-slope bottoms near deposits of drift kelp, on which they feed (Britton-Simmons et al., 2012)

In September 2018, a team operating an OceanGate submersible commissioned by SeaDoc Society observed a red urchin and drift kelp at 284 m depth near the San Juan Islands, which more than doubles the known depth range for this species.

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Dichotomous Keys:
  Flora and Fairbanks, 1966
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
  Gotshall and Laurent, 1979
  Kozloff, 1993
  Lambert and Austin, 2007
  O'Clair and O'Clair, 1998

Scientific Articles:

Breen, P.A., W. Carolsfield, and K.L. Yamanaka, 1985.  Social behaviour of juvenile red sea urchins, Strongylocentrotus franciscanus (Agassiz).  Journal of Experimental Marine Biology and Ecology 92: 45-61

Britton-Simmons, Kevin H., Alison L. Rhoades, Robert E. Pacunski, Aaron W.E. Galloway, Alexander T. Lowe, Elizabeth A. Sosik, Megan N. Dethier, and David O. Duggins, 2012.  Habitat and bathymetry influence the landscape-scale distribution and abundance of drift macrophytes and associated invertebrates.  Limnology and Oceanography 57:1 pp. 176-184

Ebert, Thomas A., 1998.  An analysis of the importance of Allee effects in management of the red sea urchin Strongylocentrotus franciscanus.  pp. 619-627 in Rich Mooi and Malcolm Telford (eds), Echinoderms: San Francisco.  Proceedings of the Ninth International Echinoderm Conference, San Francisco, California USA 5-9 August 1996.

Elbert, T.A., S.C. Schroeter, J.D.Dixon, and P. Kalvass, 1994.  Settlement patterns of red and purple sea urchins (Strongylocentrotus franciscanus and S. purpuratus) in California, USA.  Marine Ecology Progress Series 111: 41-52

Ebert, Thomas A., and John R. Southon, 2003.  Red sea urchins (Strongylocentrotus franciscanus) can live over 100 years: confirmation with A-bomb 14carbon.  U.S. Fishery Bulletin 101(4): 915-922

Levitan, D.R., M.A. Sewell, and F-S. Chia, 1992.  How distribution and abundance influence fertilization success in the sea urchin Strongylocentrotus franciscanus.  Ecology 73: 248-254

McCloskey, L.R., 1970.  A new species of Dulichia (Amphipoda, Podoceridae) commensal with a sea urchin.  Pacific Science 24: pp 90-98

McEdward, Larry R. and Benjamin G. Miner, 2006.  Estimation and interpretation of egg provisioning in marine invertebrates.  Integrative and Comparative Biology 46:3 pp 224-232

Miller, B.A. and R.B. Emlet, 1997.  Influence of nearshore hydrodynamics on larval abundance and settlement of Strongylocentrotus franciscanus and S. purpuratus in the Oregon upwelling zone.  Marine Ecology Progress Series 148: 83-94

Moberg, P.E. and R.S. Burton, 2000.  Genetic heterogeneity among adult and recruit red sea urchins, Strongylocentrotus franciscanus.  Marine Biology 136:5 pp 773-784

Nishizaki, Michael T. and Josef Daniel Ackerman, 2005.  A secondary chemical cue facilitates juvenile-adult postsettlement associations in red sea urchins.  Limnology and Oceanography 50(1): 354-362

Quinn, James F., Stephen R. Wing, and Louis W. Botsford, 1993. Harvest refugia in marine invertebrate fisheries: models and applications to the red sea urchin, Strongylocentrotus franciscanus. American Zoologist 33: pp. 537-550

Rogers-Bennett, Laura, Donald W. Rogers, William A. Bennett, and Thomas A. Ebert, 2003.  Modeling red sea urchin (Strongylocentrotus franciscanus) growth using six growth functions.  U.S. Fishery Bulletin 101(3): 614-626

Rogers-Bennet, L., H.C. Fastenau, and C.M. Dewees, 1998.  Recovery of red sea urchin beds following experimental harvest.  pp. 805-809 in Rich Mooi and Malcolm Telford (eds), Echinoderms: San Francisco.  Proceedings of the Ninth International Echinoderm Conference, San Francisco, California USA 5-9 August 1996.

Schroeter, S.C., J.D. Dixon, T.A. Ebert, and J.V. Rankin, 1996.  Effects of kelp forests Macrocystis pyrifera on the larval distribution and settlement of red and purple sea urchins Strongylocentrotus franciscanus and S. purpuratus.  Marine Ecology Progress Series 133: 125-134

General Notes and Observations:  Locations, abundances, unusual behaviors:

Another individual, collected off Sares Head July 1997.  Photo by Dave Cowles

As with all true urchins, the mouth (Aristotle's lantern, with 5 movable jaws, each of which has a movable tooth) is in the center of the underside (oral side)
Photo by Dave Cowles, July 1997

This urchin was accidentally broken open.  Inside one can see the aristotle's lantern apparatus at bottom center around the mouth, the orange eggs clustered in the gonads on the upper side, the pinkish gut spiraling around inside the test, and lines of diaphanous gray ampullae (bases of the tube feet) lining the inside of the ambulacral region on the test

Aristotle's lantern pieces

This photo shows the disassembled parts of an Aristotle's lantern from this species. A few of the pieces are missing. Photo by Dave Cowles, July 2020


As with all urchins, the internal ossicles are sutured together into a united shell-like structure called a test. Photo by Dave Cowles, July 2020

S. franciscanus spines are long, taper gradually, and are much larger than those of other local species.  Contrast these with spines of S. purpuratus, which are only about 2 cm or less long.

In this night photo, the fecal strands of the symbiotic amphipod Dulichia rhabdoplastis can be seen streaming from the spine tips.
Underwater, night photo by Jim Nestler, July 2005

With Dulichia
Another individual with Dulichia rhabdoplastis, from 13 m depth at Coffin Rocks.  2014 photo by Dave Cowles 
baby baby
This tiny individual was found under a rock by Bethany Reiswig, July 2007.  Photos by Bethany Reiswig.

An underwater photo by Kirt Onthank, July 2007

This baby S. franciscanus is  only 1.4 cm test diameter. Photo by Dave Cowles, July 2019


Authors and Editors of Page:
Dave Cowles (2005):  Created original page