ORIGINS, STRUCTURE, AND TROPHIC SIGNIFICANCE OF AMORPHOUS SESTON IN A BLACKWATER RIVER

1. The role of suspended organic aggregates in aquatic systems has received much attention, but their origin and function vary between environments and conditions. 2. In the Ogeechee River (Georgia, U.S.A.) particles are constructed of clay, organic debris, and microorganisms in a matrix of mucopolysaccharide fibrils. Although these fibrils are probably of bacterial origin, microcosm studies suggest that synthesis of particles from dissolved substances can occur in the absence of microbial processing. 3. Processing of organic material and production of amorphous aggregates occurs through a series of microbial events and follows a well-defined successional cycle that results in a high concentration of protists in sestonic particles. 4. Chemical analyses show that the relatively high protein and fat content of this amorphous material is a valuable food resource for filter-feeding macroinvertebrates that are dense in this system.