Oyster Reef Habitats
     

Oyster reefs are built primarily by the eastern oyster, Crassostrea virginica, through successive reproduction and settlement of larvae onto existing reef structure. Oysters in Florida spawn from late spring through the fall. The planktonic larvae that develop require a hard substratum to settle upon in order to complete development to the juvenile stage, and prefer to settle on the shells of other oysters. Thus, over time, continued settlement and subsequent growth of generations of oysters may form massive reef structures consisting of staggering numbers of individuals. Luntz (1960), estimated that 5,895 oysters, the equivalent of 45 bushels, occurred within a single square yard of oyster reef.

As successive generations of oysters settle and grow, reefs become highly complex, with many structural irregularities and infoldings that provide a wealth of microhabitats for many different species of animals. Wells (1961) listed 303 different species utilizing oyster reef as habitat in North Carolina. Common Indian River Lagoon species associated with oyster reefs include bivalves such as the hard clam (Mercenaria mercenaria) and bay scallop (Argopecten irradians concentricus); space competitors such as the scorched mussel (Brachidontes exustus), ribbed mussel (Geukensia demissa), the jingle shell (Anomia simplex), and barnacles of the Balanus genus; gastropod mollusks such as the conchs (Melongena spp. and Strombas spp.) and rocksnails (Thais spp.); numerous sponge species; flatworms; polychaete worms; amphipods; isopods; shrimp; and fishes such as blennies, gobies, spadefish, snappers, drum, and seatrout, among others.

Beyond providing smaller organisms with habitat, oyster reefs also provide food to a wide variety of secondary consumers. Many species of fish prey upon oyster reef associates; while others such as the black drum (Pogonias cromis) and cow-nosed ray (Rhinoptera bonasus) prey upon oysters themselves. Other species that utilize oyster reefs for foraging and feeding include the xanthid crabs, also known as mud crabs; swimming crabs of the genus Callinectes; mollusks such as the thick lipped oyster drill (Eupleura caudata), the sharp-rib drill (E. sulcidentata), the Atlantic oyster drill (Urosalpinx cinerea), the Tampa drill (U. tampaensis), the knobbed whelk (Busycon carica), the lighthire whelk (B. contrarium), and the pear whelk (B. spiratum pyruloides); flatworms such as oyster leeches (Stylochus spp.); boring sponges (Cliona spp.); and annelid worms (Polydora spp.).

Oyster reefs also contribute to improved water quality in areas where they occur. Oysters are filter feeders which strain microalgae, suspended particulate organic matter, and possibly dissolved organic matter from the water column over their gills in order to feed. Under optimal temperature and salinity conditions, a single oyster may filter as much as 15 liters of water per hour, up to 1500 times its body volume. Spread over an entire reef, for an entire day, the potential for oysters to improve water clarity is immense. Additionally, since oysters are sessile, and bioaccumulate some potential toxins and pollutants found in the water column, they have been used to assess the environmental health of some areas.

Over-harvesting, as well as persistent diseases such as MSX and Dermo have taken a devastating toll on many oyster populations along the east and Gulf coasts. In recent years, oyster reef restoration has been a concern for resource managers all along the East Coast of the United States, but especially in areas where oyster harvesting has historically been commercially important. In the late 1800s, for example, annual oyster harvests in the southeastern United States routinely topped 10 million pounds per year, and peaked in 1908 when the harvest was nearly 20 million pounds. However, annual harvests since that time have declined steadily. Today, annual harvests for oysters in the southeast averages approximately 3 million pounds per year. In many areas, efforts are underway to revitalize depleted oyster reefs and encourage growth of new reefs. For example, the Florida Department of Agriculture has stockpiled calico scallop shells from processors and placed these on depleted oyster reefs from the spring through the fall spawning periods, when larvae are most abundant in the water column. Oyster larvae, having a preference for settling on shell material, then attach themselves onto the newly placed shells and metamorphose to the juvenile stage. These young oysters, under optimal conditions, will grow to marketable size in as little as 18 – 24 months.

Click a highlighted link to read more about individual species:

Further Reading:  

Bahr, L.M. and W.P. Lanier. 1981. The Ecology of Intertidal Oyster Reefs of the  
     South  Atlantic Coast: a Community Profile. U.S. Fish and Wildlife Service, Blot.
     Program, Washington D.C. FWS/OBS 81/15. 105 pp.

Burrell, V.G. 1986. Species Profiles: Life Histories and Environmental Requirements
     of Coastal Fishes and Invertebrates (South Atlantic): American Oyster. U.S. Fish
     and Wildlife Service.  Biological Report 82(11.57). U.S. Army Corps of
     Engineers. TR EL-82-4. 17 pp.

Kumari, Siva, and C. Solis. 1995. The State of the Bay: a Characterization of the
     Galveston Bay Ecosystem. Rice university, Houston, TX. Accessed on-line at:
     www.rice.edu/armadillo/Galveston/Chap3/oyster.html.

Livingston, Robert J. 1990. Inshore Marine Habitats. In: Ecosystems of Florida,  
     Ronald L. Myers and John J. Ewel, Eds. University of Central Florida Press,
     Orlando, FL. Pp. 549-573.

Lunz, G.R., Jr. 1960. Intertidal Oysters. Wards Natl. Sci. Bull. 34(1): 3-7

Wells, H.W. 1961. The Fauna of Oyster Beds with Special Reference to the Salinity
     Factor. Ecological Monographs 31(3): 239-266.

Report by:  K. Hill, Smithsonian Marine Station
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Page last updated: June 23,  2002