CHAPTER 3 

 OYSTER REEF DESCRIPTION AND SYNECOLOGY 



The objective of this chapter is to 

 detail the intertidal oyster reef commun- 

 ity in the study area. The following sec- 

 tions will describe the reef, physically 

 and biologically, to set the stage for 

 Chapter 4 in which we discuss the rela- 

 tionship of the reef subsystem to the 

 entire estuarine ecosystem. 



Much of the material in this chapter 

 was taken from Bahr (1974), the only 

 available study that treats the entire 

 reef community (in Georgia) quantitative- 

 ly. Extrapolations of the results from 

 Bahr (1974) to the entire study area 

 should be made cautiously, and with the 

 understanding that in South Carolina estu- 

 aries, oysters in reefs are less dense 

 and net growth is more significant than 

 is the case in Georgia (S. Stevens, Uni- 

 versity of Georgia, Sapelo Island; pers. 

 comm. ) . 



3.1 GENERAL REEF DESCRIPTION 



Intertidal oyster reefs range in size 

 from small scattered clumps to massive 

 solid mounds of living oysters and dead 

 shells. Reefs are limited to the middle 

 portion of the intertidal zone, where min- 

 imum inundation time determines the maxi- 

 mum elevation of reef growth. Predation 

 and siltation limit oyster populations in 

 the lower intertidal and subtidal zones to 

 scattered individuals. 



The following passage by Dean (1892) 

 describes intertidal oyster reefs or 

 "ledges" in South Carolina at the turn of 

 the century. 



Often at low tide the oyster ledges 

 appear to the eye curiously like a 

 low hedge of frosted herbage, gray- 

 ish-green in color. A nearer view 

 discloses branching clusters or 

 clumps of oysters, densely packed 

 together, whose crowded individuals 

 now become modified or distorted 

 according to their position on the 



cluster. The individuals that cap 

 the cluster project upward like flat- 

 tipped fingers, slender, narrow, and 

 long, whose shape has given them 

 throughout the South the names "cat 

 tongues," "raccoon paws," or "rac- 

 coons." In many localities, as 

 throughout the region of Skull Creek, 

 the raccoon ledges, continuing for 

 ages to encroach upon the stream bed, 

 have formed vast oyster flats, acres, 

 sometimes miles, in extent. 



During exposure to the atmosphere 

 (ebb tide), the surface of a reef dries 

 and turns gray, but upon wetting, a living 

 reef appears greenish-brown due to a thin 

 film of algae. In contrast, piles of dead 

 shells in the intertidal zone (wet or dry) 

 generally are less colorful than are liv- 

 ing reefs. 



A section through a typical reef is 

 depicted in Figure 13. The uppermost por- 

 tion is level but slopes steeply at the 

 edges. The living portion of a reef is 

 thicker at the perimeter than in the cen- 

 ter, where mud trapped by biodeposition 

 and sedimentation smothers the oysters. 

 This sedimentation results from suspended 

 matter settling out as turbid water slows 

 down while passing over a reef. 



Often the surface of a reef is uni- 

 formly covered with oysters closely wedged 

 together, so that it is difficult to re- 

 move an individual clump. Once a hole is 

 made in a reef, however, adjacent oysters, 

 lacking support, tend to fall toward the 

 cavity and are readily removed. Most ma- 

 ture oysters are long and narrow, and vir- 

 tually all are oriented with their growing 

 edges facing upwards (Figure 14). These 

 are the typical "coon oysters" described 

 in Galtsoff (1964). They seem to grow 

 toward the least disturbed water, like 

 branches on a tree seeking light, and away 

 from encroaching sediment beneath. A sim- 

 ilar growth pattern on a much smaller 

 scale was proposed for colonies of the 

 freshwater bryozoan, Lophopodella carteri . 



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