Shellfish Restoration and Aquaculture

Justification

   The eastern oyster, Crassostrea virginica, ranges naturally from the Gulf of Saint Lawrence in Canada to the Gulf of Mexico, the Caribbean, and the coasts of Brazil and Argentina.  The eastern oyster is one of the few oyster species that can construct extensive reefs that, like corals, are primarily dead shell with a veneer of live animals.  The eastern oyster may be found on subtidal or intertidal reefs and provides important ecological functions in estuaries throughout its geographic range. These functions are related to both the reef structure formed by oysters and the filtering activity by individual oysters. Oyster reefs  support over 300 species of marine organisms that are part of the food web leading to economically important species. Oysters are capable of filtering four gallons of water per hour of water and are effective in reducing phytoplankton densities and improving water quality. As a result, oyster reefs are critical to maintaining species diversity and the natural production of estuaries where oyster reefs have had a dominant historical presence.

   With the decline of historically important areas such as Chesapeake Bay, the Gulf of Mexico supplies about 72% of the national production and the state of Louisiana is the biggest producer of oysters.  Gulf oysters are harvested manually (by hand and with tongs, also know as oyster rakes) and mechanically (with towed scrape dredges) from public waters or private leases in areas that are approved for harvesting by state health authorities.

   In 2003 the Auburn University Shellfish Laboratory (AUSL) was dedicated.  AUSL is located on Dauphin Island, Alabama and is a branch of the Department of Fisheries and Allied Aquacultures of Auburn University. 

Auburn University Shellfish Laboratory, Dauphin Island, AL

Objectives

1. Determine reasons for the decline in oyster reef productivity along the eastern shore of Mobile Bay.
2. Develop management procedures that help restore unproductive reefs in Mobile Bay.
3. Implement oyster restoration programs to increase the number of acres of oyster reefs
4. Develop sustainable shellfish aquaculture techniques as alternatives for oyster harvesters.

Research

Shellfish Restoration

Researchers are conducting assessments on the bottom of Mobile Bay to determine physical conditions on unproductive reefs. They are also monitoring water quality and sedimentation in the general area of the reefs and adding oyster shell substrate to old reef sites to see if viable populations can be reestablished.

Hypoxia

Hypoxia tolerance in oysters and the potential for developing oysters more tolerant to low dissolved oxygen is being studied.  Oysters with low oxygen tolerance would aid restoration efforts in areas where low dissolved oxygen is a limiting factor. 

Cultch Size

In an effort to improve our efficiency in getting research oysters through the hatchery phase, AUSL undertakes projects to investigate the optimal size cultch material to use when setting larvae for the production of single oysters.  In the past, ground oyster shell sieved to a size range of 250-300 microns was used with good success producing single oysters. In this project, larger cultch sizes, 600-1000 microns and 1500-2000 microns, were compared with the smaller cultch.  The 600–1000 micron cultch provided the best combination of single oysters and fast growth.

Shellfish Aquaculture

The AUSL also conducts research on shellfish aquaculture.  Past research has focused on site selection, stocking rates and grow-out for on-bottom and off-bottom oyster culture.  Future research efforts will concentrate on refining initial findings from previous experiments and expanding the project to include hard clam culture.

   An Oyster Gardening Project consists of volunteers around Mobile Bay raising oysters on waterfront property for restoration of oyster reefs. Oyster spat grown by AUSL is provided to the volunteers.

 Spreading oyster shell on the bottom of

 Mobile Bay to restore oyster reefs                                    Natural oyster reef, Mobile Bay

 

 

 

 

 

Anticipated Benefits 

   Restored reefs not only increase oyster populations for commercial production, but also improve fishing and contribute to the health of Mobile Bay. Mobile bay is a nationally significant estuary that provides a host of important economic benefits to the state and the nation.

Investigators