substantially affect the microbial 

 associations. Studies of microbes in the 

 absence of their predators are not 

 sufficient if comparisons with natural 

 ^unctions are intended (White 1Q83). 



Recent studies indicate that 

 estuarine microbial associations in 

 polvhaline areas of the bay are actually 

 controlled by epibenthic predators 

 (Federle et al. 1'383). Replicate areas (^ 

 m'') of mud-flat sediment were caqed in the 

 field to confine and exclude predators. 

 Uncaqed areas were used as controls. The 

 microbiota of the sediments was 

 characterized at weeks 0, ?, and fi by 

 measurement of the concentrations o^" 

 phospholipid and analysis of the fatty 

 acids of the microbial lipids extracted 

 from the sediments. The data were 

 analyzed using an analysis of variance and 

 step-wise discriminant analysis. After ? 

 weeks, the microbiota of the predator- 

 exclusion area was significantly different 

 from that in the control and predator 

 inclusion areas. After R weeks, these 

 differences became more pronounced. There 

 were no demonstrable caqing effects that 

 could account for the treatment 

 differences. The results indicated that 

 removal of predators had a profound effect 

 on the microbial communities in estuarine 

 sediments. Thus, we see that the 

 intermediate trophic levels (epibenthic 

 predators) of the estuarine food webs are 

 part of the control mechanism that defines 

 the structure and level of productivity of 

 the microbial communities. 



Sediments and particulate matter 

 deposited in the estuary form a substrate 

 for microbial productivity, which is 

 stimulated by dissolved nutrients in 

 various forms (Figure ?'i). The 

 transformation of dissolved substances 

 into living particulate matter produces 

 the food of important grouos of grazing 

 organisms, which, in turn, represent the 

 base of the detrital food webs in the 

 estuary. Grazing and other physical 

 disturbances enhance microbial 

 productivity and alter the qualitative 

 composition and succession of the 

 microbial community. The oeriodic input 

 of particulate organic matter and 



RIVER FLOW 

 RUNOFF LOW SALINITY 



DISSOLVED NUTRIENTS 



INCREASED MICROBIAL 

 BIOMASS 



TIDAL SUBSIDY 

 WIND 

 DISTURBANCE 



II 



PHB/LIPIDS 

 '"COj RELEASE 

 Oj UTILIZATION 



y 



BASE, DETRITAL FOOD WEBS 



Figure 25. Tentative model of microbial 

 interactions with various physical and 

 biological processes in the Apalachicola 

 River estuary (Livingston 1983c). 



dissolved nutrients into a shallow bay 

 ecosystem characterized by gradients of 

 salinity is seen to provide the appro- 

 priate components for a highly productive 

 system. Tidal and wind-induced currents, 

 periodic flooding, and predation all 

 provide a series of disturbances that, 

 together with the periodic enrichment of 

 the system from upland runoff, increase 

 microbial productivity. River flow and 

 fresh water runoFf from associated 

 wetlands, together with the shallowness of 

 the system and tidal/wind energy 

 subsidies, all contribute to the observed 

 high productivity of the estuary. 

 Considering their immense biomass and 

 their role as processors of nutrients into 

 biologically active material, the microbes 

 are an important component in the energy 

 transformations within the system. 



42 



