microaggreqates from the marshes occur 

 during the fall as river flow and rainfall 

 are minimal. By late fall (November), 

 temperature drops and salinity 

 coincidental ly increases to an annual 

 maximum throughout the estuary. Bv 

 winter, temperature is low as river flow 

 once again rises. 



Even though the input from various 

 sources is variable in terms of magnitude 

 over time, the input of particulate 

 organic matter to the estuarv from all 

 sources is fairlv constant. Thus, there 

 is a generally continuous influx of 

 dissolved and particulate organic and 

 inorganic matter to the estuary throughout 

 the year; this matter is then subiect to 

 various processes, physical and 

 biological, which are dependent on 

 specific spatial-temporal habitat 

 conditions. 



3.3. MICROBIAL ECOLOGY 



In the Apalachicola estuarv, 

 approximately 0.005'^ of the sediment dry 

 weight is composed of bacterial biomass 

 (organic carbon) and COQ"^ is composed of 

 extracellular carbohydrates (D. C. White, 

 Florida State University; pers. comm.). 

 Usually, these microbes are concentrated 

 on particulate surfaces as morphologically 

 diverse prokaryotic and microeukarvotic 

 assemblages (White 1*^83). The ecological 

 importance of microbes to the estuary is 

 defined by microbial biomass (which forms 

 the basis of food webs) and microbial 

 metabolic activity (which contributes to 

 various bioqeochemical and recycling 

 processes). White and his coworkers have 

 quantified the biochemical "siqnature" 

 components of specific microbial community 

 associations. These components include 

 phospholipids, adenine- containing 

 components, muramic acid, and hydroxy 

 fatty acids, which orovide biomass 

 estimates. Community composition has been 

 evaluated by analysis of phosoholipid 

 alkyl fatty acids (prokaryotes 

 microeukaryotes) and "signature" lioids 

 (anaerobic-aerobic bacteria). Fatty acids 

 are an excellent measure of algae, and 

 other groups of microeukaryotes can be 

 characterized by the polyenoic fatty acid 

 composition (Federle et al. 1°83). 

 Nutritional status was analyzed by 

 measurement of poly-beta-hydroxy alkonates 



(PHA), extracellular qlycolalyn, and other 

 microbial byproducts (White 1<583). These 

 methods were used to analyze microbial 

 activity in the Apalachicola estuarv. 



A series of experiments have been 

 carried out to learn the fate of 

 particulate organic matter deposited in 

 the estuary as a result of river flooding. 

 Morrison et al. (I'^^y) demonstrated a 

 succession of microbiota that colonized 

 oak leaves deposited in the estuarv. 

 Initially, colonization is by bacteria 

 with a hiqh ratio of muramic acid to ATP. 

 These bacteria are succeeded by diatoms 

 and fungal mycelia that do not contain 

 muramic acid. Thus, initial bacterial 

 colonization is succeeded by a community 

 of fungi and microeukaryotes. Bobbie et 

 al. (1078) found that microbial 

 communities on biodeqradable substrates 

 such as leaf matter are biochemically and 

 morpholoqicall y more diverse than those on 

 bioloqically inert substrates. A 10-fold 

 increase in biomass on the bioloqical sub- 

 strates was also noted. Grazinq amphipods 

 removed microbiota without affectinq the 

 morphology of oak leaves (Morrison and 

 White 1980). The colonization of mixed 

 hardwood leaves from the Apalachicola 

 flood plain in the estuary varied more as 

 a function of leaf surface than of 

 location (White et al . 1977, 1979a, b). 

 However, macroorganisms were attracted to 

 the litter baskets as a function of 

 location rather than microbial biomass 

 (Livingston unpublished data). 



The activities of microbes are 

 inextricably linked with orqanisms at 

 hiqher levels of the estuarine food web 

 (Figure ?5). Amphipod distribution was 

 significantly correlated with concentra- 

 tions of certain bacterial fatty acids 

 (White et al. 1979a, b). Amphioods 

 grazing at natural densities induced 

 increases in microbial biomass, oxygen 

 utilization, PHB synthesis, lioid syn- 

 thesis, and I'^CO^ release from simple sub- 

 stances by microbes (Morrison and White 

 1980). These chanqes caused qrazinq 

 shifts in community structure from diatom- 

 funqal-bacterial associations to 

 bacterially dominated ones. Within 

 limits, grazing thus stimulates microbial 

 growth and alters the microbial communitv. 

 Indications are that organisms graze on 

 detrital and sedimentary microbiota and 



41 



