CHAPTER 6. SUMMARY AND MANAGEMENT IMPLICATIONS AND GUIDELINES 



6.1 SUMMARY AND OYSTER REEF SIGNIFICANCE 



The American oyster ( Crassostrea vir- 

 qlnica ) is not only an extremely valuable 

 commodity to man but is also a cosmopol- 

 itan, physiologically plastic, and ecolog- 

 ically interesting estuarine organism. 

 Its natural range spans the Atlantic coast 

 and much of the gulf coast, and its ge- 

 neric "brothers" exist in coastal systems 

 worldwide. 



One intriguing aspect of oyster be- 

 havior is its propensity, under certain 

 conditions, to form massive, discrete, 

 intertidal colonies, or reefs. The larg- 

 est individual oyster reefs formed by the 

 American oyster occur in open bays along 

 the northern gulf coast. Some reefs are 

 many kilometers in length; they consist 

 mainly of dead shells, and their geometry 

 is partially the result of reworking by 

 storm surges. 



In the South Atlantic Bight, tidal 

 amplitude ranges from 1 m to over 3 m (3 

 to 10 ft), and oyster reefs occur in close 

 association with extensive salt marshes 

 characteristic of the area. Oyster reefs 

 within this region achieve a greater ele- 

 vation above mean sea level and a greater 

 oyster density (in terms of numbers and 

 biomass) than in any other coastal region. 

 The structure and ecological function of 

 these reefs are the subjects of the pre- 

 vious five chapters. 



Whereas most oyster research has been 

 carried out at the individual or popula- 

 tion level of detail, this paper has em- 

 phasized the behavior of the oyster at the 

 ecosystem level. The reef community de- 

 scribed throughout this community profile 

 exhibits characteristics and has ecosystem 

 importance that could not be predicted 

 from even "perfect" knowledge of the bio- 

 logy of individual oysters. Thus, just as 

 a termite colony is more than a collection 

 of termites, so an oyster reef shows emer- 

 gent properties, including its capability 

 of extending the intertidal range of the 

 reef assemblage upward beyond the eleva- 

 tion at which individual oysters normally 



could survive. Oyster reefs possess the 

 following characteristic properties: (1) 

 individual oysters in a reef must grow 

 with a strong vertical orientation to sur- 

 vive; (2) individual reefs strictly are 

 limited to the intertidal zone, and the 

 geometry of a given reef is strongly 

 determined by mean water level, sediment 

 stability, and current regime; and (3) 

 patterns of reef distribution are discern- 

 able within drainage basins, such that 

 reef density is usually maximal at inter- 

 mediate channel widths and current veloc- 

 ities. In other words, if all living oys- 

 ters in a drainage basin were redistrib- 

 uted either randomly or homogeneously 

 throughout the ecosystem, a large portion 

 of the function (and value) of the oyster 

 community would be lost. 



One primary ecosystem value of the 

 oyster reef community relates to its phys- 

 ical, rather than its biological, proper- 

 ties. Mature reefs are stabilizing influ- 

 ences on erosional processes and may mod- 

 ify long-term changes in tidal stream flow 

 and overall marsh physiography, although 

 these effects have not been quantified 

 yet. 



The extent of the physical influence 

 of reefs on the marsh system is a function 

 of the average relative proportion of reef 

 area to total intertidal area in a given 

 drainage basin. The available estimates 

 of this relationship vary, but about 0.05% 

 of reef area to total intertidal area 

 (marsh and water) may be a reasonable 

 estimate. 



Another aspect of the ecosystem value 

 of oyster reefs relates, in natural estua- 

 rine areas, to reefs' being stable islands 

 of hard substrate in an otherwise unstable 

 soft muddy environment. These islands are 

 essential habitat for some organisms, 

 especially the sessile suspension-feeding 

 epifauna usually limited by the available 

 surface area. Reefs also provide a highly 

 irregular surface with crevices that serve 

 as havens for motile invertebrates; and 

 some small fish use reefs for shelter 

 during flood tides. Oyster reefs are 



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