sewage, and/or fertilizer; (4) toxins. 

 Including pulp mill sulfites, heavy met- 

 als, chlorinated hydrocarbons, organophos- 

 phates, radionuclides, and petroleum 

 hydrocarbons; (5) physical impairment of 

 feeding structures by oil; (6) thermal 

 loading, primarily from power plants; (7) 

 overharvesting; and (8) wetland loss due 

 to development. 



These perturbations can be lethal or 

 sublethal for oysters, but even when sub- 

 lethal, the oysters may be unfit for con- 

 sumption either by humans or by other 

 predators. Oysters, like most suspension 

 feeders, efficiently concentrate suspended 

 and dissolved constituents of the water 

 column to levels several orders of magni- 

 tude above background concentrations (bio- 

 accumulation). Human pathogens, pesti- 

 cides, and heavy metals are prime exam- 

 ples. Greig and Wenzloff (1978) reported 

 that oysters with high levels of heavy 

 metals in their tissues did not purge or 

 lose these metals rapidly when transferred 

 to clean water. 



Quantifying sublethal effects on oys- 

 ters is complicated by the fact that oys- 

 ters live at the water sediment interface, 

 and most pollutant concentrations in sed- 

 iments are different from those in water. 

 While very low concentrations of some 

 toxins in oysters, like dioxin, may be 

 significant, the capability to detect 

 these pollutants has been achieved only 

 recently, so that much recent literature 

 on pesticide residues in oysters and other 

 organisms may be misleading (e.g., Buqq 

 et al. 1967). 



The effect of crude oil extracts on 

 the carbon budget of Mytilus edulis , the 

 edible mussel, is illustrated in Figure 

 11. As shown, carbon ingested and assimi- 

 lated declines with increasing oil concen- 

 tration. Comparable effects could be 

 expected for the oyster. 



The estuaries in the study area are 

 presently not as severely impacted by man- 

 induced (cultural) change as are some 

 other oyster-producing areas, such as sec- 

 tions of the Louisiana and Florida coasts, 

 Chesapeake Bay, and Long Island Sound. In 

 addition, intertidal reefs are in some 

 ways more resistant to man-induced pertur- 

 bations (e.g., salinity intrusion and 



resultant susceptibility to predation) 

 because of the periodic exposure due to 

 tides. Conversely, intertidal reef exis- 

 tence is already stressful, and added 

 stress may inhibit reef formation. 



Effects of marsh alteration in Texas 

 have decreased local oyster production 

 (Moore and Trent 1971). Changes in hy- 

 drology and pollution have probably con- 

 tributed to local declines in oyster reef 

 density in the Savannah, Georgia, area. 

 Historical change in intertidal oyster 

 reefs in the study area, caused by both 

 natural and cultural perturbations, is 

 discussed in Section 4.2. 



Harvest of Intertidal Oysters 



Because this paper's overall objec- 

 tive is to describe the ecological func- 

 tion and importance of the oyster reef as 

 a component of the coastal ecosystem in 

 the study area, we include here only a 

 brief discussion of several aspects of 

 exploitation of reef oysters by man. More 

 information on the present commercial har- 

 vest and potential for future exploitation 

 may be found in Gracy and Keith (1972), 

 Keith and Gracy (1972), and Gracy et al. 

 (1978). These references are for South 

 Carolina, where commercial harvest is con- 

 centrated in the study area. 



(1) Oyster harvest by man has been 

 an important cultural activity since long 

 before recorded history (at least as early 

 as 2000 B.C., Keith and Gracy 1972). Nu- 

 merous oyster shell middens and shell 

 rings of apparent ceremonial significance 

 in the study area attest to the importance 

 of the oyster in the diet of early coastal 

 residents. Many oyster shells found in 

 these artifacts are large and thick, 

 which, when considered in light of the 

 presence of many whelk and oyster drill 

 shells, indicate that a significant por- 

 tion of the prehistorically harvested oys- 

 ters were of subtidal origin. 



(2) Recent oyster harvest in the 

 study area, however, is primarily concen- 

 trated on intertidal oyster populations. 

 This harvest, both recreational and com- 

 mercial, involves the very labor-intensive 

 and time-consuming removal of clumps of 

 oysters from exposed mud flats, an effort 



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