Organisms Associated with Oyster Habitats

Oysters are the building blocks of the hard substrate benthic (bottom) community. Over time, you should begin to see many organisms that are common to natural oyster bars, such as barnacles, mussels, bryozans, and worms. While some are predators of oyster spat, most of these organisms are not a threat to oyster survival. Mussels, for example, may compete with oysters for food while barnacles do not generally cause any serious problems unless the barnacles are extremely abundant. (This is because barnacles feed on a different component of plankton.) Other organisms such as filamentous algae and sea squirts can cause problems when they grow too heavily on oysters.

You will also find several kinds of fish and crabs that concentrate around oysters. Some are simply feeding on associated organisms, some are there for protection themselves, and some are there to lay eggs and use oyster shell as a nursery for producing their young. The diversity of plants and animals found on oyster bars illustrates the important habitat role oysters play in the Bay system.

1. Oyster spat 2. Skilletfish 3. Hooked mussels

4. Whip mud worms 5. Sea Squirts 6. Sea anemone

7. Barnacles 8. Fan worms 9. Mud crab

Oyster Disease and Their Impact on Oyster

Oysters in the Chesapeake Bay and other waters in the mid-Atlantic have been severely impacted by parasitic disease, in particular Dermo ( Perkinsus marinus) and MSX ( Haplosporidium nelsoni). Even with good natural sets of oysters in the Bay, many oysters do not survive the three years it generally takes to reach harvest size.

Oysters infected with the parasite that causes Dermo eventually become weakened and die - this may not occur until the second or third year of growth. When the oyster dies, its tissue rots and the infective stages of the parasite are released into the water. Nearby oysters can ingest these spores through their filtering activity and become infected; this usually happens during the late summer or early fall in our region. The mode of transmission for MSX is still not fully understood, though its virulence is controlled to some extent by lower salinity (usually below 15 parts pet thousand).

While spat produced in hatcheries for the oyster gardening program will be initially free of disease, these oysters can eventually contract Dermo and, in high salinity regions, MSX. However, even if there are large losses in your garden, the survivors may be valuable for planting as future brood stock. These survivors potentially have a natural tolerance for disease, which could be passed on to their progeny. So please return your oysters to the Chesapeake Bay Foundation for planting on sanctuary reefs, even if many of them are dead. CBF will make sure your oysters are placed on an appropriate reef so as not to spread disease.

Ongoing research efforts are attempting to breed oysters that are resistant to disease. As these superior strains become available, every effort will be made to distribute them to oyster gardeners in a way that will most benefit the overall restoration effort.

To learn more about oyster diseases, visit these sites:

• Restoring Oysters to U.S. Coastal Waters
• More about MSX
• More about Dermo

This page was last modified October 17, 2012

The Oyster Gardening Program is a cooperative effort of the Oyster Alliance
Chesapeake Bay Foundation ~ Maryland Sea Grant Extension Program
University of Maryland Center for Environmental Science ~ Oyster Recovery Partnership

This page is part of Maryland Sea Grant's Oyster web site.

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