Oyster Changes in Store When Wetlands Are Restored

On a good day, the world may be your oyster, but if you're a coastal Louisianian, day in and day out the oyster might be your whole world. Oysters and oystering are the basis of a unique culture in southern Louisiana. For some families, generation after generation have devoted their lives to growing, harvesting and selling oysters. Like many industries, however, oystering is seeing changes, and some of those changes could come from efforts to restore Louisiana's coastal wetlands.

Despite oysters' ability to withstand wide variations in water salinity, drastic changes, like the constant introduction of fresh water into a traditionally brackish area, will kill resident oyster beds. Many of the proposed efforts to restore or protect Louisiana's coastal wetlands will require just such an introduction of large amounts of fresh water.

Will this freshwater influx destroy Louisiana's oyster industry? No, but it will change things. Most significantly, some oyster beds might ultimately be displaced. "It's easiest to visualize if you see a line in the water where the oyster beds are," says one expert. "If the line is currently at Point A, by the time you introduce a large amount of fresh water near that location, you alter the salt content in the water and the line will move towards saltier water. It won't disappear. It simply moves farther away, and so will the oysters."

An Oyster Bed: Present Day		In the illustration at left, an oyster bed is indicated by the black area, surrounded by brackish water (shown in gray) near the mouth of a freshwater estuary, such as a bayou or river.
		A Change in Location: 3-5 Years in the Future
In this illustration, increased freshwater flow in the nearby estuary has constructed new deltaic wetlands but also altered the salinity of the bay. With the change in water conditions, the original oyster bed has died off and a new oyster bed has developed in the newly-established brackish conditions. It is important to note, however, that this development is not immediate. It could take from three to seven years for this new bed to develop.

Unfortunately, neither market nor seed oysters simply move when they want to — they don't move at all. It will take time — probably a few years — for the oysters in the swimming veliger stage to re-establish themselves in new brackish conditions. So, why introduce fresh water and displace the oysters? Because fresh water is the primary ingredient for building new marsh. It's important to remember that fresh water carries nutrients and sediment. As fresh water is constantly moved into a new area, the nutrients nourish the marsh plants that help hold the soil in place. If there is sufficient sediment in the water, the sediment builds up, or accretes. Eventually, new surface rises out of the water, plants spring up, and a new marsh is born.

And healthy marsh is crucial to the continued viability of both oysters and oystering in Louisiana. As marsh decays, it forms the detritus and nutrients that grow the oyster's food. And, in addition to providing habitat for a wide variety of species, the coastal wetlands play a vital role in keeping salt water from intruding too far inland. Remember that oysters survive best in brackish water — water that isn't totally fresh or totally salt. In either of those environments, oysters eventually die. Also, most new wetlands that will be created near existing oyster beds will ultimately become brackish. Over the long term, creating new freshwater wetlands now will guarantee brackish areas in the future, thereby guaranteeing a future for oysters and oysterers.

Failing to build new marsh will only allow salt water to intrude farther and faster. Before long, much of the marsh will be gone and there will be no fuel for the estuarine food web. Salt water will have moved inland, and oysters and oystering families alike will be gone.