Oysters may seem to be passive creatures, but when it comes to the economy and ecology of Alabama's Gulf Coast, they're dynamic, vital players. Research under way through Auburn University's Peaks of Excellence Program is helping insure that oysters can continue to do their important work.
According to Rick Wallace, professor of fisheries and allied aquacultures at Auburn, oysters have always been important to Alabamans. The Southeast's Paleo Indians used oysters for food, tools, jewelry and currency thousands of years before the first Europeans arrived. Early European settlers in America also used oysters for food and tools and even as construction material for buildings and roads.
Oysters developed into a cash crop and today Alabama's oyster fishery contributes an estimated $3.4 million to the coastal economy annually. Wallace, who works on a variety of shellfish projects at the AU Marine Extension and Research Center in Mobile, said that oysters impact much more than the seafood market.
"Oyster reefs provide food and shelter to a host of organisms that, in turn, nourish some 300 species of fish and shellfish, many of which are economically important," said Wallace, who also is a marine specialist with the Alabama Cooperative Extension System. "And oysters improve water quality in the Mobile Bay estuary by filtering tremendous quantities of algae and some suspended organic matter."
In short, oysters are mighty important for lots of reasons. However, despite the fact that they have sustained life and cleaned our waters for centuries, oysters are facing some challenges in the modern world.
Oyster bed productivity has been declining through the years and oyster yields are erratic. Wallace said that Alabama has harvested an average of one million pounds per year since the 1880s. However, large fluctuations occur on a year-to-year basis. For example, 1.5 million pounds of oysters were harvested in 1982 while only 336,000 pounds were harvested in 1983.
Wallace explained that oysters' immobile lifestyles may partially explain the declines. Because oysters remain in one location once their larvae settle on a substrate, they are at the mercy of the water brought to them by currents and tides. If the water is too fresh or too salty, they can die. They also can be smothered by sand and silt from dredging operations or extremely heavy storms. Thus, any environmental changes — be they caused by Mother Nature or human activity — can severely affect oysters.
Low oxygen events (such as the Mobile Bay "jubilee" phenomenon), high sedimentation, a limited supply of newly hatched oysters (larvae) and limited oyster shell substrate for larvae to attach to are also suspected contributors to the decline of these once productive oyster reefs.
To answer questions about the declines and fluctuations in oyster populations and to increase oyster yield and quality for the food market, AU has been studying a wide range of oyster management programs for many years. David Rouse, now chair of the AU Department of Fisheries and Allied Aquacultures, and Wallace have spent more than 20 years exploring oyster issues. Today, several Peaks projects are under way. In one, AU researchers assessed Fish River Reef, which once covered about 70 acres along the Eastern Shore of Mobile Bay.
This area contains several historically productive oyster reefs that are not producing commercial quantities of oysters despite the fact that these beds have not been fished commercially in many years. The Marine Resources Division (MRD) of the Alabama Department of Conservation and Natural Resources conserves oysters by requiring licenses, enforcing a harvest size limit of three inches and allowing only hand or oyster tong harvest on public reefs. The MRD also has worked to rejuvenate declining oyster reefs by augmenting them with additional oyster shells and planting hatchery-grown oysters on the sites.
According to Wallace, initial reef assessment studies in 1998 revealed low oyster density (less than 0.1 oyster per square yard) and a lack of shell substrate for larval oysters to settle on. Hatchery-produced oysters planted on the oyster shell plots at the reef grew well for more than a year and young oysters were found in the area, indicating adequate recruitment of juvenile oysters.
In the second year of the study, low oxygen events (levels near zero) occurred in bottom water at the study site. Low oxygen concentrations from August 1998 through September 1999 were often associated with increases in salinity and sometimes associated with neap tides (minimal tidal movement). Sediment accumulated on the shell pads at rates greater than at productive reefs and killed all the young that summer.
Results of this study indicate that oyster larvae are present and they can attach and survive when adequate substrate is available. However, periodic low oxygen concentrations and possibly high sedimentation rates are contributing to the failure of some oyster reefs. Some of this problem may simply be where the oysters are located in the water profile.
Last year MRD added additional shell to the areas, which raised the oyster beds up off the bottom of the Bay and may improve the survivability of the oysters by changing their location in the water stream.
"We're monitoring that situation now," Wallace said, "and this information is being used to formulate new strategies for oyster reef restoration projects in Mobile Bay."