Changes in microbial community structure related to biodegradation of eelgrass (Zostera marina)

Seagrass meadows produce organic carbon and deposit it on the seabed through the decaying process. Microbial activity is closely related to the process of eelgrass death and collapse. We investigated the microbial community structure of eelgrass during the eelgrass decomposition process by using a microcosm containing raw seawater and excised eelgrass leaves collected from a Zostera marina bed in Futtsu, Chiba Prefecture, Japan. The fast-growing microbes (i.e., Alphaproteobacteria, Gammaproteobacteria, and Flavobacteriia) rapidly adhered to the eelgrass leaf surface and proliferated in the first two weeks but gradually decreased the relative abundance as the months moved on. On the other hand, the slow-growing microbes (i.e., Cytophagia, Anaerolineae, Thaumarchaeota, and Actinobacteria) became predominant over the eelgrass surface late in the culture experiment (120, 180 days). The fast-growing groups of Gammaproteobacteria and Flavobacteriia appear to be closely related to the initial decomposition of eelgrass, especially the rapid decomposition of leaf-derived biopolymers. Changes in nitrogen content due to the bacterial rapid consumption of readily degradable organic carbon induced changes in the community structure at the early stage of eelgrass decomposition. In addition, shifts in the C/N ratio were driven by microbial community changes during later decomposition phases.