OYSTER REEFS OF THE GULF OF MEXICO 



By W. Armstrong Price, Agricultural and Mechanical College of Texas 



Caswell Grave (1901, 1905) showed that linear, 

 ridge-shaped reefs of the common edible estuarine 

 oyster now known as Crassostrea rinjinica develop 

 from shell clusters at the more favorable shoreline 

 or near-shore positions, growing out into a passing 

 current and elongate at right angles to it, then 

 branch or curve as the current is deflected by reef 

 extension. This process seems to be valid for the 

 reefs found in the bortlering areas of many bays 

 and estuaries. Another class of reefs, elongated 

 parallel with median channels, does not follow 

 Grave's process of terminal growth into a current 

 from its flank but forms along a channel and 

 elongates parallel with the dominant currents of 

 the channel. Paired reefs of this type are found 

 in many inner water bodies, as in central San 

 Antonio Bay, Texas, and the lower James River, 

 Virginia. The reefs of Atlantic estuarine rivers 

 seem usually to be merely elevated ridges on large, 

 oval to quadrate oyster beds. Those of the Gulf 

 coast are not characteristically surrounded by 

 thickly occupied oyster bottoms except along their 

 immediate flanks. 



Besides the linear ridge-shaped reefs, many 

 short ridges, or rounded to oval forms are charted, 

 locally called tow-heads. 



Mudshell dredgers report that some reefs have 

 a total depth of some 18 feet or more, in places 

 with an interbedded layer or two of mud. Many 

 reefs of Texas bays reach lengths of 1 or 2 miles, 

 a few being 4 to 5 miles long. The longest reef 

 complexes known are the two that curve broadly 

 across the wide mouth of Atchafalaya Bay, Louisi- 

 ana. The outer, more recenth' active reef complex 

 is 25 miles long with many narrow channels 

 through it. The older is dead and buried by 

 several feet of sediment. 



The known oyster reefs of most regions occur in 

 the inner bays and estuaries in waters neither too 

 exposed to heavy wave action nor too fresh from 



' Contribution from the Department of Oceanography of the Agricultural 

 and Mechanical College of Texas, College Station, Texas, No. 27. 



incoming alluvium-laden river waters. They seem 

 to form chiefly on the more stable bottom areas. 

 Along parts of the northwestern coast of peninsular 

 Florida (28°15'-30°04' N. Lat.), off the mouth of 

 Atchafalaya Bay, Louisiana, and on the south and 

 west shores of Marsh Island just west of the ])ay, 

 reefs of Crassostrea virginica occui' in the Gulf of 

 Mexico within 5 or 6 miles from shore. Here, the 

 Gulf waters are locally diluted to the necessary 

 brackish ness. 



Several of the small reefs off Atchafalaya Bay 

 have live oysters. Here a large flow of fresh 

 water from the Mississippi enters the Gulf 

 through its largest distributary, the Atchafalaya 

 River. Off the northwestern coast of Florida 

 compact limestones form the floor of the shallowly 

 submerged continental shelf. The peninsula has 

 a widespread artesian water body fed by surface 

 waters entering through the extensively fissured 

 limestones and the many sink holes of the karst 

 topography. Numerous up-welling springs are 

 reported in the stream mouths along this coast, 

 and a few have been reported in the Gulf. The 

 very broad, shallow, gently-sloping continental 

 shelf protects the near-shore waters from breakers 

 and surf, producing conditions in the Gulf similar 

 to a lagoonal environment. The oyster reefs 

 occur in these quiet waters of lowered salinity. 

 They are distributed near shore where the artesian 

 groundwater maps show the 1 0-foot contour on 

 the piezometric surface to be at the shoreline. 

 These Gulf reefs include forms that project out 

 from a shoreline and also broadly curved and offset 

 forms that are roughh^ parallel to the coast. Groups 

 of the latter have jumbled patterns of occurrence. 



LITERATURE CITED 



Grave, Caswell. 



1901. The oyster reefs of North Carolina. A geological 



and economic study. Johns Hopkins Univ., Circular 



No. 151, 9 pp., April, 1901. 

 1905. Investigations for the promotion of the oyster 



industry of North Carolina. Rept. U. S. Fish Comm., 



1903, 29: 247-.341. Washington. 



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