IMPULSE investigated how Posidonia oceanica meadows, vital for Mediterranean coastal biodiversity, are supported by interactions with invertebrates and their microbial communities. These interactions are essential for seagrass ecosystem functioning and resilience but had been largely overlooked in conservation and restoration plans. The project focused on the association between P. oceanica and the sponge Chondrilla nucula, evaluating how the presence or absence of the sponge and its microbiome affected seagrass productivity. IMPULSE also examined the partnership’s role in carbon and nitrogen cycling and its seasonal dynamics, shedding light on the ecological mechanisms that sustain healthy seagrass ecosystems.