densely populated with mussels, mud crabs, 

 polychaetes, barnacles, and other macro- 

 fauna, and countless smaller metazoa, pro- 

 tozoa and bacteria. 



The members of the oyster reef com- 

 munity are limited primarily to suspension 

 and deposit feeding macrofaunal consumers. 

 The trophic role of this macrofaunal com- 

 munity as a whole assimilates carbon de- 

 rived from phytoplankton and detrital 

 sources and makes it available to higher 

 consumers, i.e, terrestrial and aquatic 

 animals. Of the former, raccoons and 

 birds like oyster catchers and grackles 

 are predators on oyster reefs. Aquatic 

 consumers that prey on healthy living oys- 

 ters include the blue crab ( Callinectes 

 sapidus ) and the black drum ( Poqonias 

 cromis ). Many other aquatic carnivores 

 undoubtedly visit oyster reefs during 

 flood tides and prey on the host of small 

 invertebrates residing there. 



More important than the food web 

 roles of oyster reef inhabitants in the 

 salt marsh estuarine system is their role 

 in mineralizing organic carbon and releas- 

 ing nitrogen and phosphorus in forms 

 usable by the primary producers. The 

 significance of the energetic roles of the 

 reef community is exemplified by the meta- 

 bolic rates of the entire community being 

 among the highest measured for any benthic 

 community (27,000 kcal/m2/yr). This rate 

 is partly due to the great surface area in 

 a reef, supporting a large population of 

 aerobic bacteria, and to the high biomass 

 of the resident macrofauna (up to 1,100 g 

 afdw/m2). 



Each summer the reef community con- 

 tributes a stream of high quality protein 

 to the water column in the form of gametes 

 and larvae of oysters and other resident 

 macrofauna. These meroplankton (or larvae) 

 are food for nektonic filter feeders, food 

 for other benthic organisms, and recruits 

 for the next generation of reef oysters 

 and associates. Because reefs continually 

 subside into the mud, new generations of 

 oysters at the top are necessary to main- 

 tain the steady state elevation of the 

 upper reef surface. 



Oyster growth in mature reefs appears 

 extremely slow, and some of the larger 

 resident oysters probably are 5 to 10 or 



more years of age. They are typically long 

 and narrow and usually display a watery 

 condition with little glycogen reserves, a 

 sign of stress or being spawned out. 



Because oysters in reefs apparently 

 live close to their stress tolerance 

 threshold, further perturbation by man can 

 easily destroy the entire reef community. 

 Reefs are particularly susceptible to 

 artificial hydrologic changes, such as 

 those that follow the impoundment or 

 diversion of waterbodies as large as 

 coastal rivers or as small as individual 

 tidal streams. Reefs primarily are found 

 at the interface between wetland and open 

 water, and the destruction of wetlands for 

 any reason results in a decrease in this 

 interface zone. Oysters and other benthic 

 macrofauna are, of course, also connected 

 to and depend upon wetland macrophytes via 

 trophic pathways still not well under- 

 stood. 



Reef oysters are susceptible to the 

 increasing array of man-made chemicals and 

 heavy metals becoming more prevalent in 

 coastal waters. They are also vulnerable 

 to the eutrophic effects of fertilizer- 

 and sewage-loading in coastal waters 

 through the potential alteration of the 

 composition of the natural phytoplankton 

 community in a manner that may be less 

 desirable or even toxic to oysters. 



Reef oysters have evolved to tolerate 

 high levels of turbidity, but increased 

 sedimentation on top of natural levels can 

 smother them. Dredging related to shell 

 or phosphate mining, navigation or pipe- 

 line canals, or other construction activi- 

 ties in the coastal zone can drastically 

 increase the natural sediment load in 

 local areas. In addition, the artificial 

 mixing of reduced bottom sediments with 

 water above the bottom can deplete the 

 water column of its dissolved oxygen. 



Direct physical alteration of mature 

 oyster reefs, e.g., by harvesting, can 

 destroy an entire reef, even if the reef 

 is only moderately disturbed. Harvest of 

 intertidal oysters is productive only on 

 immature oyster reefs low in the inter- 

 tidal zone, where oysters are not as 

 crowded as in mature reefs and where 

 growth is more rapid. Thus, mature reefs 

 are most valuable to the ecosystem and to 



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