SCORE

Oyster Biology & Ecology

Scientific Name: Crassostrea virginica

Common Names: Eastern oyster, American oyster

Classification:

Kingdom Animalia
Phylum Mollusca
Class Pelecypoda or Bivalvia
Order Lamellibranchia
Family Filibranchia
Genus Crassostrea
species virginica

Range and Habitat

The American or eastern oyster is found along the Atlantic and Gulf of Mexico coasts of North America. Oysters form reefs, which are a dominant feature of many coastal estuaries. Oysters are often considered a "keystone species," providing valuable shelter and habitat for many other estuarine organisms, improving water quality, and reducing bank erosion.

Oysters are typically found in estuaries, sounds, bays, and tidal creeks from brackish water (5 parts per thousand [ppt] salinity) to full strength seawater (35 ppt salinity). Oysters are tolerant organisms, able to withstand wide variations in temperature, salinity, and concentrations of suspended sediments and dissolved oxygen. Throughout much of its range, the oyster occurs mostly in subtidal areas. But in South Carolina, almost all oysters live in the intertidal zone. Intertidal oysters typically have elongated, irregularly shaped shells. When submerged by the tide, oysters feed by filtering phytoplankton (microscopic plants) from the water column.

Explore the image below to identify and learn about organisms commonly found in South Carolina estuaries, a typical environment for oysters.

acorn barnacle American oystercatcher Atlantic croaker Atlantic marsh fiddler Atlantic sharpnose shark black sea bass blue crab bottlenosed dolphin eastern brown pelican eastern oyster	Florida stone crab great blue heron hard clam knobbed whelk longwrist hermit crab marsh grass shrimp ribbed-mussel red drum red-winged blackbird	sheepshead short-billed marsh wren smooth cordgrass snowy egret southern flounder southern stingray spotted seatrout striped mullet tarpon

Life Cycle

Adult oysters begin reproduction when water temperatures become greater than 68�F (~20�C). In South Carolina this generally occurs from May through October. Oysters are broadcast spawners, meaning they release eggs and sperm into the water column. A fertilized egg develops into a planktonic (free-swimming) trochophore larva in about 6 hours. A fully shelled veliger larva is formed within 12 to 24 hours. The larva remains planktonic for about three weeks. Towards the end of this period it develops a foot (hence, pediveliger) and settles to the bottom of the water column where it seeks a hard substrate. When a suitable surface (ideally adult oyster shell) is located, the larva cements itself and metamorphoses to the adult form. This newly attached oyster is known as a "spat."

Reef Ecology

Oysters are the building blocks of one of the most important benthic communities in South Carolina estuaries, the oyster reef. Formed as a result of years of oyster production and settlement in concentrated areas, reefs have become home to a complex assemblage of animals and plants. Benefits of oyster reefs to the coastal environment include the following:

• Providing solid structure within the water column for sessile (permanently attached or fixed) organisms (for example, barnacles and sea anemones)

• Creating homes and hiding places for organisms seeking refuge from predation (for example, polychaete worms and soft-shell blue crabs)

• Providing spawning substrate for fishes (for example, gobies, blennies, and skilletfish)

• Stabilizing bottom sediments for benthic organisms (for example, hard clams) and aquatic plants

• Concentrating prey (food) species for larger predator fishes (for example, striped bass)

• Serving as breakwaters to protect adjacent shorelines from erosion

• Filtration and clarification of water

Some of the information in this section is modified from Oysters in the Environment found at www.mdsg.umd.edu.

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For more information on the SCORE program, email score@dnr.sc.gov or contact Nancy Hadley (843.953.9841) or Michael Hodges (843.953.9241) with the South Carolina Department of Natural Resources (SCDNR).