It is increasingly recognized that invertebrate-bacterial associations can have profound effects on host ecology and evolution, and on benthic biogeochemistry. These associations may be of particular relevance in seagrass ecosystems. In this project, we explore the idea that invertebrate-bacterial associations may have an outsized role in N transformation processes through the combined effect of their bioturbation activity (creating microhabitats for specific bacterial populations) and the activity of their associated microbiome. Through a combination of field surveys and incubation experiments, using complementary methods such as biochemical essays, stable isotope probing (SIP), 3D micro profiling of chemical elements, and high-throughput sequencing (HTS), we will uncover the taxonomic and functional diversity of the microbiome and the contribution of invertebrate-bacterial associations to biogeochemical fluxes of N at the ecosystem level.