limited to areas with significant tidal 

 amplitudes ordinarily associated with rel- 

 atively high salinity coastal environ- 

 ments. The effect of long-term salinity 

 changes on oyster reefs has not been 

 reported (see Section 4.2). The reef life 

 style allows oysters to invade the preda- 

 tor-rich, high salinity zones of estua- 

 ries. Predators are excluded because of 

 the reef's daily exposure to the atmos- 

 phere resulting from the ebb and flood of 

 the tides. 



Reef Surface Area 



The surface area of oysters and dead 

 shells in a series of reef samples was 

 measured by Bahr (1974). He calculated 

 that at least 50 m^ of surface area is 

 available for habitation by epifauna for 

 every square meter of overall reef area. 

 The production of this large, highly ir- 

 regular surface area is an important 

 aspect of the functional role of the oys- 

 ter. In the marsh-estuarine ecosystem that 

 is relatively devoid of hard substrate, 

 the oyster provides this limited resource 

 for other oysters and for the associated 

 macrofauna that will be described in the 

 next section. 



3.2 REEF-ASSOCIATED MACROFAUNA 



A total of 42 species of macrofauna 

 (or groups of related species) represent- 

 ing seven phyla are associated with the 

 oyster reef community in Georgia (Table 

 3). This is only a fraction of the 303 

 species listed by Wells (1961) in his 

 monograph on the fauna of subtidal and 

 intertidal oyster beds, but slightly more 

 than the 37 species found by Dame (1979) 

 in South Carolina reef samples. Rarely 

 present and thus not shown in Table 3 are 

 unidentified species of boring sponges, 

 bryozoans, hydroids, and mites; all of 

 these, except mites, occur abundantly on 

 subtidal oysters but only incidentally in 

 the intertidal reef community. Probably a 

 maximum of 50 macrofaunal species, includ- 

 ing those not readily separable, occur in 

 the community samples on which these num- 

 bers are based (Bahr 1974). Twenty-one 

 species occurred in the majority of the 

 samples; 17 occurred in 93% or more sam- 

 ples; 8 species occurred in every sample. 

 Mean frequencies for each reef species 



over the entire sampling period and rela- 

 tive frequency of each species are listed 

 in Table 4. The biomass and relative bio- 

 mass of each major species or group of 

 species are given in Table 5. No relation- 

 ship between the size of reefs and the 

 macrofaunal community was observed by Bahr 

 (1974) although a theory exists that indi- 

 cates a direct (positive) relationship 

 between reef size and species richness 

 (Simberloff 1974; Jackson 1977). 



A comparison of the results of Dame's 

 reef survey with the reef macrofauna data 

 reported by Bahr (1974) indicates that 

 Dame found slightly fewer species or 

 groups of related species (Table 3). Dame 

 also found a lower density of macrofauna, 

 by an order of magnitude (about 3,300 in- 

 dividuals/m^ compared to about 38,000/m2 

 reported by Bahr). Some of these differ- 

 ences may result from differences in sam- 

 pling technique since Dame sieved his oys- 

 ter reef sediment samples through a 1.0-mm 

 screen, whereas Bahr used a 0.5-irjTi mesh 

 screen. 



Lehman (1974) reported 31 species of 

 invertebrate organisms or groups of relat- 

 ed organisms from oyster reefs in Crystal 

 River, Florida. Of these, only nine spe- 

 cies were also found by Bahr (1974) to be 

 associated with Georgia reefs. Lehman re- 

 ported the total abundance of reef-associ- 

 ated organisms to be about 6,200/m2 and 

 oyster density to be about 3,800/m2 in his 

 control area. His estimate of biomass of 

 oyster reef associated organisms was 135g/ 

 m^ dry wt. 



Specific groups of organisms that 

 reside in oyster reefs in the study area 

 will be discussed below. 



Oyster Commensals 



The relationship between the oyster 

 pea crab ( Pinnotheres ) and the oyster 

 represents inquilinism, an association 

 slightly detrimental to the host species 

 (Nicol 1960). Beach (1969) reported that 

 Pinnotheres becomes increasingly rare in 

 oysters in the higher portions of the 

 intertidal zone. Dame (1970) found only 

 about 1% incidence of pea crabs among 

 intertidal oysters in South Carolina; 

 likewise, Bahr (1974) found only a 3% 

 incidence. 



42 



