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Oyster Reefs in Galveston Bay

Clusters of oyster shell, live oysters and other commensal organisms (organisms that live in close association with one another) form a distinct oyster reef habitat. Oyster reefs tend to form on hard substrate where sufficient current exists to transport planktonic food to the filter‑feeding oysters. Eastern oysters (Crassostrea virginica) are the dominant oyster species and have a valuable ecological role as filter‑feeders in the estuary. A large, healthy oyster population is able to filter large volumes of bay water, and can influence con­ditions such as water clarity and phytoplankton abundance. At the same time, oysters' propensity to bioaccumulate some pollutants, com­bined with their lack of mobility, make them an important indicator organism for determining the health of the estuary.

The reefs in Galveston Bay form in the open bay, along the periphery of marshes, and near passes and cuts, and can be either subtidal or intertidal. The reef itself is three‑dimensional because oyster larvae settle on the top of old shells growing upwards through the water column above the established oysters. The shells, cemented together, create an irregular surface that supports a myriad of micro­habitats for smaller species.

The Importance of Oyster Reef Communities

The oyster reef community is very diverse. While Eastern oysters are dominant, other bivalve mollusks, gas­tropods, barnacles, crabs, amphipods, isopods, and polychaete worms are normal­ly abundant. Although shallow reefs often have some primary production from algae growing on the shells, they are dependent on the importation of food resources from open-bay water and peripheral marshes. Plankton is filtered from the water moving over the reef. Predators in this habitat include fish capable of crushing mollusks (such as black drum); blue crabs and stone crabs, which prey on small oysters with thin shells; and oyster drills, snails that prey on oysters by drilling a hole through their shell. At low tide, birds  forage on the exposed oyster reef habitat.

Oyster reefs are a significant ecological feature of Galveston Bay that has commercial importance as well.  A large amount of oyster biomass is transferred from Galveston Bay to human-dominated systems every year by the oyster fishery. The Texas Parks and Wildlife Department (TPWD) estimates that prior to Hurricane Ike, commercial landings of Eastern oysters from Galveston Bay represented 80 percent of the oysters harvested in Texas. The annual Galveston Bay oyster harvest totaled approximately 3 million pounds worth nearly $10 million. Because of their ecological and economic importance, oyster reefs are targeted for restoration and creation.

Loss and Restoration of Oyster Reefs

When Houston was first settled, an ancient oyster reef (Redfish Bar) separated Upper and Lower Galveston Bay. This reef stretched from Smith Point on the east to Eagle Point on the west and had only one small gap through which shallow draft boats could pass. There were extensive oyster reefs throughout Trinity, East and West Bays as well. In the latter half of the 19th century, oyster shell became a construction material and was commercially harvested. In the first half of the 20th century, oyster shell became an industrial commodity and shell dredging intensified. Millions of cubic yards of oyster shell were removed from the bay, some of it from living reefs. This practice greatly reduced the area covered by oyster reef habitat, but was prohibited in 1969. Since 1969, oyster reef area has been increasing and some oyster reef has been created. Restoration projects have focused on the creation of oyster reef by shell placement. Both intertidal and subtidal oyster reef creation has been implemented. It is too early to assess the long-term success of current approaches to oyster reef creation.

Hurrican Ike had a tremendous impact on oyster reef habitat in Galveston Bay. TPWD estimates that approximately 60 percent of the oyster reef habitat in Galveston Bay was covered by sediments as the storm surge moved through the bay in September 2008. Scientists do not know how long it will take for the reefs to recover. Until then, the commercial oyster harvest in Galveston Bay will be greatly reduced.

Public Health and Oyster Reefs 

Raw or partially cooked oysters can be a source of illness for people if the oysters are contaminated by pathogens. To protect public health, the Texas Department of State Health Services (DSHS) conducts monitoring of oyster waters for the National Shellfish Sanitation Program on a routine basis. Based on their monitoring data, the DSHS classifies areas of the bay for oyster harvesting. As of 2008, approximately 383 square miles (64 percent) of Galveston Bay waters are classified in one of three categories: conditionally approved, restricted and prohibited. The remainder (36 percent or 220 square miles) is approved for direct harvest. The prohibited category is the smallest in extent (22 square miles), but is deemed by the DSHS to pose a significant risk of illness to shellfish consumers.

The risk of illness is not determined directly, but is addressed by measuring concentrations of fecal coliform bac­teria as an indicator organism. These bacteria indicate the contami­nation of waters by wastes from birds or mammals (including humans) that could also contain much more dangerous pathogens, for example those causing Hepatitis A. Wet weather runoff is the most significant source of bacteria. Based on measurements of fecal coliform bacteria in water and oysters, and by establishing relationships between rainfall runoff and elevated fecal coliform levels, shellfish harvest area maps are pro­duced by the DSHS and utilized by commer­cial fishermen and the public to determine where oyster harvest can safely and legally occur.

Additional Information 

 

Literature Cited:

Powell, E. N., J. Song, and M. Ellis. 1994. The status of oyster reefs in Galveston Bay, Texas. Webster, Texas, Galveston Bay National Estuary Program Publication GBNEP-37.

Turney, J. G. 1958. Shell surveys of Galveston Bay. Houston, Texas, Horton and Horton.


 

 

 

Related Pages:

Habitat
Seafood Safety

 Oyster Reef DistributionMap depicting the distribution of oyster reefs in Galveston Bay. Data source: Powell et al. 1994; Turney 1958.

 

 

 

Clusters of live oysters and other commensal organisms can be seen here. Photo courtesy Galveston Bay Foundation.

 

 

 

 

Oyster reef restoration projects are ongoing in Galveston Bay. Photo courtesy Galveston Bay Foundation.

 

 

 

 

 

Seafood Harvest Areasshellfish harvest restrictions map, data sources Texas Department of State Health ServicesMap depicting the 2009 shellfish harvest area classifications in Galveston Bay. Data source: Texas Department of State Health Services.

 
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