SALT MARSH SUBSTRATE INTERACTION: MICROORGANISMS 



Roger B. Hanson 



Skidaway Institute of Oceanography 

 Savannah, Georgia 31406 



INTRODUCTION 



Odum (1971) described several ideas 

 of ecological succession, and a summary 

 of those characteristics describing com- 

 munity development are presented in Ta- 

 ble 1. The creation of a coastal ecosys- 

 tem from dredged materials will begin 

 with an orderly process in community de- 

 velopment. The succession in the commun- 

 ity will proceed from an unstable low 

 biomass environment and eventually cul- 

 minate in a stable high biomass ecosys- 

 tem. In the early stages of community 

 succession, the rate of primary produc- 

 tion will generally exceed the rate of 

 community respiration. However, as de- 

 velopment proceeds, the ratio of primary 

 production to community respiration will 

 approach one. But, when production ex- 

 ceeds respiration, organic matter and 

 biomass will accumulate in the ecosystem 

 and the resulting production to biomass 

 ratio will decrease. 



As the ecosystem develops further, 

 organisms will be linked together in a 

 relatively simple linear food web. Pri- 

 mary production will initially support 

 the microheterotrophs (bacteria, yeast, 

 and protozoans) by supplying the neces- 

 sary organic carbon, and the meiofauna 

 and macrofauna will graze on the micro- 

 heterotrophs. As the system matures, 

 the food web will become more complex 

 and the system will switch from a graz- 

 ing food web to a detrital food web, 

 typified by the marshes in Georgia. This 

 brief review of ecosystem development 

 emphasizes the flow of energy from the 

 primary producers to the secondary pro- 

 ducers. The goal of community develop- 

 ment is to increase stability within the 

 ecosystem and to achieve a large and di- 

 verse population of organisms. Under- 

 standing the succession of benthic com- 

 munity development and production rates 

 of various populations in dredged mate- 

 rials will greatly increase our knowl- 

 edge of coastal ecosystems. 



In these proceedings several inves- 

 tigations have reported on the estab- 

 lishment of rooted aquatic plants within 

 wetland areas and dredged materials. 

 There have been only two reports about 

 invasion and colonization of dredged ma- 

 terials (Garbisch et al. 1975; Cammen 

 1976b) by macrobenthos, and there has 

 been no report that dealt with microbial 

 development in dredged materials. The 

 gap in the flow of energy between pri- 

 mary producers and macroinvertebrates 

 requires investigation. In addition, 

 there has been no report on the impor- 

 tance of microbial populations in higher 

 plant establishment in dredged materi- 

 als. Therefore, information on microbial 

 development in dredged materials is des- 

 perately needed so that comprehensive 

 guidelines can be formulated for coastal 

 ecosystem habitat development. 



METHODS 



SAMPLING SITE 



Microbial colonization in dredged 

 materials planted with marsh plants was 

 investigated at Buttermilk Sound, Geor- 

 gia, and was supported by the U.S. Corps 

 of Engineers, contract to Dr. Robert 

 Reimold. Data were collected between 

 January and September 1976. 



AERIAL VIEW OF SITE 



Buttermilk Sound Habitat Develop- 

 ment Site (BSHDS) is shown in Figure 1. 

 The dredged material (elevation 2.4 m or 

 8 ft)was graded on the eastern side of 

 the island from mean low water (MLW) to 

 mean high water (MHW). The site 5 mo 

 later showed considerable deposition of 

 sediment (clay and silt) and organic de- 

 bris above MLW (Figure 2). Below MLW, 

 sand waves were quite evident, indicat- 

 ing high energy water movement. The MLW 

 zone was very unstable, and the movement 

 of sand in the northern section of the 



35 



