CHAPTER 5. CONCEPTUAL MODELS OF THE INTERTIDAL 

 OYSTER REEF COMMUNITY 



5.1 OBJECTIVES AND LEVELS OF RESOLUTION 



This chapter summarizes some conclu- 

 sions, primarily qualitative, about the 

 significance of oyster reefs to the coast- 

 al ecosystem in the study area. The sum- 

 mary is in the form of a set of three con- 

 ceptual models that are explicit diagram- 

 matic illustrations of the interactions 

 among oyster reefs and other salt marsh 

 ecosystem components. Conceptual models 

 can provide succinct, qualitative expres- 

 sions of the feedback pathways, forcing 

 functions, and major interconnections 

 characterizing a particular ecosystem. 

 Conceptual models are usually over-simpli- 

 fications of the real world, but their 

 formulation may indicate deficiencies of 

 information that can become future re- 

 search goals. Conceptual models take a 

 variety of forms, from simple box and ar- 

 row diagrams to detailed and complex "spa- 

 ghetti" diagrams that are difficult to 

 interpret. Figure 18 (from Odum 1971) 

 illustrates one conceptual model of an 

 oyster reef that compares it in functional 

 terms to a city. 



Oyster reef organization and function 

 must be considered at different levels of 

 space and time, and our conceptual models 

 are presented at three (hierarchical) lev- 

 els of resolution: a regional level, a 

 drainage unit level, and a reef level 

 (Figure 19). The regional level model 

 treats the oyster reef system over the 

 entire study area or a large portion of 

 the study area. At the regional level, 

 detailed reef community information is 

 relatively unimportant compared with that 

 of long-term geological processes affect- 

 ing regional ecology. The relative propor- 

 tions of salt marsh, open water, and total 

 reef area and patterns of their spatial 

 distribution are particularly significant 

 at the regional level since these factors 

 are regulated by long-term geological pro- 

 cesses. 



The second level of resolution is on 

 a smaller and more detailed scale — that of 



a single marsh-estuarine drainage unit. 

 For example. Figure 20 shows the oyster 

 reef distribution in the Half Moon River 

 estuary on Wilmington Island, Georgia. 

 This tidal river and its surrounding salt 

 marsh watershed exemplify a "typical" lo- 

 cal drainage unit in which oyster reefs 

 are distributed in a nonrandom pattern. 

 At this intermediate scale of resolution, 

 the reef community is more visible than at 

 the regional level and presumably exerts a 

 more profound short-term influence on the 

 local ecosystem. Another example of the 

 resolution achievable at this level may be 

 seen in Figure 21. The information content 

 at this scale is such that only broad spa- 

 tial patterns of reef distribution within 

 the marsh-estuarine ecosystem are discern- 

 able. The perspective, then, is an "over- 

 view." At scales smaller than this (great- 

 er resolution), the oyster reef system is 

 obscured. 



The third conceptual level of resolu- 

 tion is of a discrete reef and its immedi- 

 ate surroundings. At this level, a reef 

 can be considered analogous to an individ- 

 ual in a "population" of reefs, each mem- 

 ber being influenced by local forcing 

 functions--hydrologic forces, short-term 

 episodic events, and biological phenomena, 

 such as spawning events and predation. 

 An individual reef is subject to local 

 phenomena, and its influence is primarily 

 restricted to its immediate surroundings. 

 The purpose of the third level conceptual 

 model is to summarize the specific phenom- 

 ena regulating the welfare of a given 

 reef. The cumulative effects of the "pop- 

 ulation" of reefs in a drainage basin are 

 addressed at the drainage unit level. 



Some important differences among the 

 above three conceptual levels of organi- 

 zation and function of oyster reefs in the 

 study area are summarized in Table 8. The 

 three different scales of resolution are 

 discussed in Sections 5.2, 5.3, and 5.4. 



Symbols used in the models were de- 

 veloped by H.T. Odum (1971) as a shorthand 



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