GULF OF MEXICO 



481 



sistently high. Although oysters exist here the 

 envu-onment is just as marginal as in the first 

 category considered. The population is again 

 characterized by its sparseness, slow growth rates, 

 and excessive mortality. The dearth of suitable 

 cultch and the high concentration of predators are 

 important factors in the low sm-vival rate of the 

 spatfall. In most years the commercial impor- 

 tance and the reproductive capacity of reefs in 

 this location are of negligible importance. Fol- 

 lowing disastrous floods this community, by pro- 

 viding larvae, may be the all-important factor in 

 repopulating the flooded areas where the oysters 

 have been destroyed. 



Factors other than salinity levels may exert a 

 profound influence in determining the character 

 of the oyster community. The most important 

 among these are the nature of the bottom, the 

 type of cultch, the amount of water current 

 canning a supply of food, and the degree of 

 artificial cultivation. It is significant that when 

 young oysters are moved to a new environment 

 they quickly acquire the attributes of the popu- 

 lation already present there. It is also of interest 

 to note those instances in which a characteristic 

 type of oyster has acquired a geographical name 

 and becomes well-known in the trade. The prac- 

 tical oysterman may discover that there are other 

 geographic locations which produce essentially 

 the same type of oyster; perhaps we find that 100 

 boatloads of "name" oysters are annually mar- 

 keted from a geographic area which can produce 

 only 25 boatloads. This should not be regarded 

 as a case of deception on the part of the producer, 

 for a "name" oyster actually implies a certain 

 qualitj' of product, and similar environmeuts can 

 produce oysters of essentially indistinguishable 

 quality regardless of how far apart they may be 

 geographically. 



Very specialized communities exist on wharf 

 pilings, especially in channels having a high 

 current velocity. Isolated marsh ponds may 

 produce characteristic populations. Noteworthy 

 among these is the occasional colony of "Ma- 

 rennes" oysters whose flesh is colored a deep green 

 by the abundance of a particular diatom in its 

 food supply. 



Natural oyster reefs are stUl found occasionally 

 and were quite common at the turn of the century. 

 The only essential difference in their appearance 

 from that of cultivated reefs lies in the fact that, 



being unharvested, the population builds up until 

 it breaks the water surface. At low tide many 

 oysters are exposed to the atmosphere. Growth 

 along the ridges of these reefs is usually less than 

 that of the population average. The shells are 

 polished and have a reduced number of external 

 and internal commensal organisms. The oysters 

 are scattered in small clusters. There is a coarse 

 substratum consisting primarily of shell fragments. 

 Buried inches deep in the substratum and usually 

 growing quite well, considering the seemingly 

 unorthodox position, there is often a fair number 

 of older oysters. Where depth of water over the 

 reef is greater, the clusters of oysters become 

 larger, and the individual oysters attain a larger 

 average size. Although the oysters are very long, 

 they are correspondingly narrow with deeply 

 concave attached valves and flat or even concave 

 upper valves. Attached to the older oysters may 

 be three or four, perhaps more, younger genera- 

 tions. As a rule, the quality of meat of such 

 oysters is inferior, although the amount of spawn 

 produced by them may be tremendous. The 

 periphery of these reefs is often sharply defined, 

 the outermost fringe of oysters showing luxuriant 

 growth, while a foot beyond lies a muddy ooze too 

 soft to support a single shell. 



The interdependence of the myriad of animals 

 associated in this oyster community forms a 

 complex system. In a stable environment then- 

 numbers and variety are strictly controlled by the 

 availability of habitat niches even though their 

 food supply is primarily obtained from without. 

 Relatively slight changes in the external environ- 

 ment may drastically alter, however, the entire 

 make-up of the community. 



This description of the natural oyster commu- 

 nity is probably equally applicable to the oyster 

 community of past ages. The evidence for the 

 antiquity of the oyster in the Gulf is impressive, 

 and the early discovery of their value as food is 

 shown by the Indian shell middens which dot the 

 coast line. Vast deposits of buried shell exist in 

 all of the Gulf States. These banks are usually in 

 8 to 10 feet of water under a layer of mud of vary- 

 ing thickness. The deposits range from a few 

 inches to 25 feet and more in depth, and no one 

 knows their extent. For the most part the oysters 

 on these old reefs did not grow to any larger size, 

 i. e., live any longer, than oysters do today. The 

 average shell size in many deposits is considerably 



