occupied by Mississippi Sound was a full 

 salinity system, as shown by marine 

 foraminifera remains in sediment cores. 

 The nearshore zone was brackish, how- 

 ever, especially near the mouths of the 

 two large rivers (Pearl and Pascagoula) . 



The barrier islands formed follow- 

 ing the slowdown in sea level rise about 

 4,000 years B.P. These islands formed 

 from the accretion of bottom sediments 

 that had originally eroded from the Ala- 

 bama mainland. They formed a 230 km 

 long barrier island-shoal chain that ex- 

 tended between Dauphin Island, Alabama, 

 and the present Jefferson Parish-New 

 Orleans metropolitan area. 



Between about 3,000 and 2,300 years 

 B.P., St. Bernard delta sediments from 

 the Mississippi River prograded into the 

 gulf to about 3-20 km south of the 

 present Cat, Ship, and Horn Islands. 

 This delta reduced wave energy from the 

 west and stopped the progradation of Cat 

 Island. After the Mississippi River 

 abandoned the St. Bernard distributary, 

 erosion of delta sediments led to severe 

 erosion of Mississippi coastal marsh- 

 lands. The Chandeleur Island chain 

 formed parallel to the original delta 

 lobe shore and has since migrated west- 

 ward. 



During recent times the Mississippi 

 Sound barrier islands have been strongly 

 affected by hurricanes, as well as by 

 normal beach erosion and westward lit- 

 toral drift. Although the islands have 

 shown a net westward migration, new 

 islands have formed on the east end of 

 Mississippi Sound following the passage 

 of hurricanes. 



The Mississippi Sound Estuary 



Mississippi Sound makes up the 

 largest habitat type in the Mississippi 

 Sound hydrologic unit. This elongated 

 shallow estuary is bordered on the north 

 by a series of small bays, marshes, 

 bayous, and rivers and on the south by a 

 chain of islands. Average overall depth 

 is 2.97 m, with 3.5 to 6 m depths in 

 central areas (Otvos 1981). Fresh water 

 input is primarily through the Pearl and 

 Pascagoula drainage basins, in addition 



to minor inputs from St. Louis Bay and 

 Biloxi Bay. Mississippi River water may 

 be introduced through Chandeleur Sound 

 (Lytle and Lytle 1931) as well as 

 through Lake Borgne during openings of 

 the Bonnet Carre spillway. Marine water 

 from the gulf enters the Sound through 

 the island passes. 



Mississippi Sound is characterized 

 by low tide and wave energy, and highly 

 variable salinity. There is a dominant 

 westward littoral drift, due to pre- 

 vailing SE, S, and SW winds. Much of 

 the time the water column is uniform and 

 well mixed, and it rarely stratifies 

 (Eleuterius 1978) . 



Bottom sediments are muddy (silty- 

 clayey) in central areas and sandy along 

 island and mainland shores. Much of the 

 sound is underlain with fossil oyster 

 reefs, and the largest recent reefs 

 exist south of St. Louis Bay, (Square 

 Handkerchief, Pass Marianna, and Tele- 

 graph Reefs) with a total area of about 

 3,000 ha (7,400 acres) and a maximum 

 thickness of 4 m (Otvos 1981). 



Oysters are still common in Mis- 

 sissippi Sound, although oyster produc- 

 tion has declined significantly over 

 time. Commercial production in Missis- 

 sippi Sound peaked in the early 1900' s, 

 declined and leveled off during the 

 1950' s and 60' s, and declined further in 

 recent years. In 1979, only 41,000 

 pounds of oyster meat were harvested, 

 compared to 4,680,000 pounds in 1963 

 (Deegen et al. 1981). The decline has 

 been attributed to adverse salinities, 

 reef closure in bay waters, and storm 

 damage (Deegen et al 1981). An effort 

 is underway to restore some of the 

 oyster-growing potential through shell 

 planting by the Mississippi Bureau of 

 Marine Resources. A private leasing 

 system has also been suggested to 

 encourage improved management. Many 

 natural oyster beds are closed because 

 of increasing sewage pollution resulting 

 from increasing coastal urbanization. 



Fisheries in the Mississippi Sound 

 hydrologic unit include finfish and 

 shellfish, which are dominated by men- 

 haden and industrial bottomfish (e.g., 



93 



