Production of microbial organic aggregates from macrophyte‐derived dissolved organic material

Organic aggregates were produced in the laboratory by bubbling dissolved organic material derived from five species of coastal macrophytes. The weight of aggregates produced after bubbling was significantly related to the amount of DOC (dissolved organic C) initially present. An average of 19% of the initial DOC was converted to aggregates, 23% remained in solution, and the remaining 58% was mineralized to CO 2 . The C : N ratios of aggregates did not vary between species or runs and ranged from 4 to 12. Microscopic examination of aggregates showed that they contained large numbers of rod‐shaped bacteria. The data were interpreted to suggest that aggregates are composed of live and dead bacteria, other microbes, and extracellular material. The ingestion of aggregates of this type by consumers is a potentially important route for the flow of labile organic C in marine systems.