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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



less than that found on a modern reef of planted 

 oysters, and we may assume that they did not 

 compare in quality with the cultivated oyster of 

 today. 



The enormous quantity of shells in these buried 

 banks does not indicate an unusually high rate of 

 productivity but rather speaks for the untold 

 eons that passed in the formation of such deposits. 

 These old reefs constitute an extremely valuable 

 resource in modern times, since they are com- 

 posed of relatively pure calcium carbonate 

 (Shearon 1951). The chemical industries of 

 Texas alone, in the decade beginning 1940, con- 

 sumed more than 45 million tons of these shells. 

 Similar deposits are extensively exploited in 

 Louisiana and to a lesser extent in the other Gulf 

 States. Exam^ination of these reefs reveals strik- 

 ing simUarities to the natural communities we 

 find today. Many of the buried shells show light 

 to heavy infestations with boring sponge; some 

 shells are pitted with excavations like those made 

 by the modern boring clam; encrusting bryozoans 

 are present; and of frequent occurrence are the 

 shells of conchs, quite similar if not identical, 

 with the modern Thais. 



The diversity of habitats existing along the 

 coast of the Gulf causes a parallel diversity m the 

 pattern of growth and reproduction in the oyster 

 so that we may draw a generalized picture of the 

 course of events and indicate the significant 

 exceptions. 



In midwinter the gonad tissue of mature oj-sters 

 is inconspicuous, but by February or March, 

 depending on water temperatures, active game- 

 togenesis takes place. The gonad may form a 

 layer a quarter of an inch or more in thickness by 

 the time spawning commences in early spring, 

 but frequently its thickness is far less. The gonad 

 layer retains much of its original volume through- 

 out the summer; spawning continues regularly 

 until October. Mass spawnings of the popula- 

 tion are clearly defined and typically occur several 

 times throughout the summer in a given location 

 (Ingle 1951). This is in contrast to the condition 

 in northern waters where a single mass spawning 

 of major importance usually occurs in early 

 summer. 



Oyster larvae are found in the plankton in the 

 period from April through October. It is probable 

 that their free-swimming period is significantly 

 shorter in these waters than along the Atlantic 



coast because of the sustained higher temperature 

 levels during the summer months. The produc- 

 tion of larvae and the resulting spatfall may 

 show peaks of intensity in any one or all of the 

 summer months. At Pensacola the pattern is 

 quite variable from year to year, but during the 

 month of July larval production and spatfall are 

 consistently lower than during the rest of the 

 spawning season. These conditions contrast sig- 

 nificantly with those on the Atlantic coast. In 

 Long Island Sound, for example, although there 

 is scattered spawning during the summer period, 

 the majority of spawn is produced in a relatively 

 short time about the end of June (Loosanoff and 

 Engle, 1940). The relative abundance of larvae 

 in the plankton at Pensacola in the period 1949- 

 1951 shows a good correlation with the spatfall 

 in the area, although the quantity present at any 

 one time seems small in comparison with the 

 amount of set produced. In this area there are 

 no commercial reefs; the oyster population is 

 confined to pilings and similar locations out of 

 reach of the conch. In Mississippi Sound, where 

 the oyster reefs are extensive, 50 percent of the 

 volume of plankton samples collected during the 

 height of the spawning season may consist of 

 oyster larvae. 



Spat production is heavy but erratic all along 

 the coast; in certain localities spatfall and sur- 

 vival are particularly good. As is true on the 

 Atlantic coast, the areas of best spatfall are fre- 

 quently areas of relatively poor growth. From 

 the earliest times Louisiana oystermen trans- 

 planted seed oysters from setting grounds east of 

 the Mississippi and placed them in areas west of 

 the delta where growth is especially rapid. It is 

 quite possible that the poorer record of spat pro- 

 duction in high salinity areas is due to predation 

 rather than to a real decrease in setting rates. 

 In the Pensacola area the cumulative spatfall 

 during a season may be as high as 1,000 spat to 

 the square inch. This intensity of spatfall poses 

 a significant problem to the oyster industry. In 

 areas where oysters set heavily they become so 

 clustered in their growth that they are difficult to 

 handle commercially and have meat of inferior 

 quality. 



Competent observers have reported spatfall 

 during other months of the year at widely sepa- 

 rated points along the coast, but these instances 

 are exceptions to the general picture of larval 



