The estuarine environment (the area where salt and fresh water mix) in Louisiana is home to a large variety of mollusc species. The most important of these species from both an economic and ecological standpoint is the American Oyster (Crassostrea virginica). Oysters grow in abundance in the rich coastal waters of Louisiana and can be found naturally in dense aggregations called reefs both in the intertidal and subtidal environment. Oyster reefs comprise the majority of hard substrate found in Louisiana's coastal waters and a multitude of estuarine organisms are associated with these reefs. Many animals, including fish, crabs, worms, and meiofauna use oyster reefs as both a foraging and shelter resource.
Louisiana residents have long known of the high food value of oysters and have been cultivating the species for many years. In the early part of the 20th century, the state of Louisiana began leasing state water bottoms to private citizens for the raising and farming of oysters (prior to this time individual parish governments leased the waterbottoms). The state also maintains large acreages of water bottoms that are designated as public seed grounds and reservations. During the open oyster season, properly licensed fishermen can gather oysters from the public reefs. These public areas are actively managed to provide a steady supply of seed oysters for fishermen to transplant onto private leases.
Although the oyster is the mollusc species of most importance and interest, Louisiana estuaries also boast sizeable populations of other shellfish. Several species of clams can be found buried beneath the sediment in coastal waters and fishermen have tried to market one species, the Quahog clam (Mercenaria spp.), in years past. The Southern Oyster Drill (Stramonita haemostoma) is a predatory snail that feeds on oysters and can be extremely abundant on subtidal oyster reefs in higher salinity waters. These snails pose a serious threat to oyster populations but are collected by hand, on occasion, for use in a variety of Cajun dishes.
The Marine Fisheries Division of the Louisiana Department of Wildlife and Fisheries has developed successful oyster management plans over the last century that continue to yield a steady supply of both sack and seed oysters on the public grounds. State biologists use two gear types (dredge and square meter) when sampling the public grounds and analyze the data to determine overall health of the oyster resource. By taking random samples (with replication) from multiple locations on the public grounds, oyster abundance can be accurately predicted.
In addition to data collection and analysis, the planting of suitable hard substrate on water bottoms is also part of the management plan. The placing of substrate, called cultch deposition, provides free-swimming oyster larvae a firm attachment site on which to settle and grow. The practice of cultch deposition began in the 1930s when the state used fossil clam shell as cultch material on the seed grounds. After shell dredging was stopped in the1990s, the state looked to other possible sources and materials for cultch. Today, cultch deposition is carried out on state seed grounds using materials such as oyster shell, limestone, and crushed concrete.