Ostrea lurida Carpenter, 1864

Common name(s): Olympia Oyster, Native Pacific oyster, California oyster, Lurid oyster

Synonyms: Monociostrea vancouverensis, Ostreola conchaphila[Also see note below on Ostrea conchaphila] Ostrea lurida
Subclass Pteriomorphia 
Order Ostreida 
Superfamily Ostreoidea 
Subfamily Ostreinae 
Ostrea lurida, cultivated individuals from Taylor Shellfish Farms near Rosario.  These individuals are about 3 cm in length and 4 cm in height. The tissue is still present in the opened individual on the left.
(Photo by: Dave Cowles, August 2016 )

Description:  Bivalves in Subclass Pteriomorphia typically live attached to surfaces by cementing their shell or secreting byssal threads.  The foot is reduced or absent.  Oysters have two thick, irregular valves, but one of them (the left) is usually cemented to the substrate.  The height of the valves is usually greater than the length. The valves have no "wings" near the hinge, and have no regularly spaced radial ribs. There is only one adductor muscle scar inside the shell (photo). Genus Ostrea (flat oysters) are not as deeply cupped as are the cupped oysters (Genus Crassostrea), and they have small chomata near the ends of the hinge which Crassostrea does not have. Ostrea lurida is the only small, native oyster species normally found on our portion of the coast. It cements its left valve to a solid substrate, often a shell or rock. Its gray or white valves tend to be irregular or oval in outline and have few if any frills growing on them (although there may be irregular concentric lines). The shell is thin, and the ventral margin of the shell may be scalloped. Inside, the valves are whitish or grayish-green and slightly pearly. The height does not exceed about 8 cm, and is not usually greater than 5 or 6 cm.  Takes 4-6 years to grow to 4-5 cm height. The single adductor muscle scar inside the valves is not much darker than the rest of the inside of the valve (photo). 

How to Distinguish from Similar Species:  Both of the other oyster species on our coast can get much larger than 8 cm. Crassostrea virginica has few frills like O. lurida but may grow up to 15 cm high and has a deep blue-black adductor muscle scar. C. gigas can grow up to 25 cm in height and has substantial frills on the shell.  In a few limited areas the European flat oyster, O. edulis, is cultivated, but that species has a dark adductor muscle scar and can grow to slightly larger. O. lurida looks virtually identical to O. conchaphila which is found on the west coast of Mexico near Mazatlan and further south. In fact, there are no reliable morphological features which distinguish them and some recent papers treat our local species as O. conchaphila.  However, molecular evidence suggests it is indeed a separate species (Polson et al., 2009)

There is some discussion of whether the intertidal and subtidal populations of this species may in fact be separate but closely related species.

Geographical Range:  Pacific coast from Sitka Alaska to central Baja California, mainly in protected bays. Common locally in Willapa Bay and south Puget Sound in our area, and cultivated in some oyster farms. It is also common in San Francisco Bay and Tomales Bay in California.

Depth Range:  Intertidal to 50 m depth, mostly low intertidal or shallow subtidal.

Habitat:  Often in clumps on shells in mud, on rocks, concrete pilings, and on oyster shells.  If living on rocks it often is near the underside unless the rocks are embedded in mud; then they are on the upper side.

Biology/Natural History:  This species is a hermaphrodite, meaning that it is both male and female.  It tends towards being a protandrous hermaphrodite, which are males when they are young and females when they grow larger, but for most of its life it seems to alternate between the sexes and both gonads may be mature at the same time. It discharges large numbers of gametes at a time, sperm first followed by rapid development of eggs.  The sperm are released but the eggs are fertilized and brooded within the valves for several weeks. After the gametes are released the oyster's flesh is soft, flabby, and translucent rather than firmer and whitish in color for a period. Spawning is usually in spring and settlement of the larvae (spat) in late summer, but may occur more than once in the year if temperatures are warm. This small oyster was heavily exploited for food and commercial harvest along our coast in the 1800's, leading to commercial extinction of the species by 1930.  Noting its rapid disappearance, Washington State placed restrictions on harvest and established marine reserves starting in 1897.  However, the oyster has been very slow to recover and is still uncommon in most places. Continuing efforts are being made to help it recover. Some of the main barriers to its recovery include competition by other species, especially introduced ones, after settlement of the spat, its sensitivity to emersion, and the removal of the previously existing oyster beds which provided ideal larval settlement conditions (Trimble et al., 2009).  In the mud flats where this species often grows, burrowing shrimp such as Upogebia pugettensis and Neotrypaea californiensis may exclude them due to the sediment raised by their burrowing activity (an example of amensalism).  Parasites include several protists, including one similar to Mikrocytos (Friedman et al., 2005) and the ectoparasitic copepod Mytilicola orientalis may be present as well, especially in San Francisco Bay.



Dichotomous Keys:
  Carlton, 2007 (As O. conchaphila)
  Flora and Fairbanks, 1966
  Kozloff, 1987, 1996

General References:
  Carefoot, 1977
  Fitch, 1953
  Harbo, 1999 (As O. conchaphila)
  Harbo, 2011
  Johnson and Snook, 1955
  Kozloff, 1993
  Lamb and Hanby, 2005 (as O. conchaphila)
  Morris, 1966
  Morris et al., 1980
  Niesen 1994, 1997
  Ricketts et al., 1985
  Sept, 1999 (as O. conchaphila)

Scientific Articles:

Baker, P., 1995.  Review of ecology and fishery of the Olympia oyster, Ostrea lurida with annotated bibliography.  Journal of Shellfish Research 14: pp 501-518

Blake, Brady, and Philine S.E. Zu ermgassen, 2015. The history and decline of Ostrea lurida in Willapa Bay, WA. Journal of Shellfish Research 34:2

Cook, A.E., J.A. Shaffer, B.R. Dumbauld, and B.E. Kauffman, 2000.  A plan for rebuilding stocks of Olympia oysters (Ostrea conchaphila, Carpenter, 1857) in Washington State.  Journal of Shellfish Research 19: pp 409-412

Hopkins, A.E., 1935.  Attachment of larvae of the Olympia oyster, Ostrea lurida, to plane surfaces.  Ecology 16: pp 82-87

Hopkins, A.E., 1936. Ecological observations on spawning and early larval development in the Olympia oyster (Ostrea lurida). Ecology 17: pp 551-556

Hopkins, A.E., 1937.  Experimental observations on spawning, larval development, and setting in the Olympia oyster Ostrea lurida. Bulletin of the U.S. Bureau of Fisheries 48: pp 438-503

Friedman, Carolyn S., Heather M. Brown, Timothy W. Ewing, Frederick J. Griffin, and Gary N. Cherr, 2005.  Diseases of Aquatic Organisms 65: pp 1-8

Kirby, Michael Xavier, 2004.  Fishing down the coast: Historical expansion and collapse of oyster fisheries along continental margins.  Proceedings of the National Academy of Science 101:35 pp 13096-13099. doi 10.1073/pnas.0405150101 (as O. conchaphila)

McKernak, D.L., V. Tarter, and R. Tollefson, 1949.  An investigation of the decline of the native oyster industry of the State of Washington, with special reference to the effects of sulfite pulp mill waste on the Olympia oyster (Ostrea lurida).  State of Washington Department of Fisheries Biological Report 49A: pp 115-165

Polson, Maria P., William E. Hewson, Douglas J. Eernisse, Patrick K. Baker, and Danielle C. Zacherl, 2009.  You say Conchaphila, I say Lurida:  Molecular evidence for restricting the Olympic oyster (Ostrea lurida Carpenter) to temperate western North America.  Journal of Shellfish Research 28:1 pp 11-21. doi http://dx.doi.org/10.2983/035.028.0102

Pritchard, Catherine, Alan Shanks, Rose Rimler, Mark Oates, and Steven Rumrill, 2015. The Olympia oyster Ostrea lurida: recent advances in natural history, ecology, and restoration. Journal of Shellfish Research 34:2.

Ruesink, Jennifer L., B.E. Feist, C.J. Harvey, J.S. Hong, A.C. Trimble, and L.M. Wisehart, 2006.  Changes in productivity associated with four introduced species: ecosystem transformation of a 'pristine' estuary.  Marine Ecology Progress Series 311: pp 203-215. doi 10.3354/meps311203

Trimble, Alan C., Jennifer L. Ruesink, and Brett R. Dumbauld, 2009.  Factors preventing the recovery of a historically overexploited shellfish species, Ostrea lurida Carpenter 1864.  Journal of Shellfish Research 28:1 pp 97-106. http://dx.doi.org/10.2983/035.028.0116

White, J.M., E.R. Buhle, J.L. Ruesink, and A.C. Trimble, 2009.  Evaluation of native oyster (Ostrea lurida) status and restoration techniques in Puget Sound, Washington, USA.  Journal of Shellfish Research 28: pp107-112.  doi 10.2983/035.028.0101

Web sites:

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

Ventral view
In this ventral view the slight scalloping of the valves on the ventral margin can be seen.

In these two opened individuals it can be seen that the adductor muscle scar is visible but not much darker than the rest of the internal shell. 

Under intertidal rock
This individual was found under an intertidal rock. Photo by Dave Cowles, July 2020

Authors and Editors of Page:
Dave Cowles (2017):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University