Seagrasses are marine flowering plants that are found along temperate and tropical coastlines around the world. They provide habitat for fish, shellfish, and marine herbivores such as turtles (see the photo) and dugong and also serve important physical roles—for example, by filtering sediments and reducing wave and current energies near coasts (1). By filtering the water column of pathogens, seagrasses reduce contamination in seafood while also reducing coral disease (2). Given the global distribution of seagrass and its role in climate mitigation and food security, the protection of these ecosystems has implications for the planetary boundaries within which humanity can safely operate (3, 4). Growing understanding of the roles of seagrass shows that their protection is crucial for staying within safe planetary boundaries and sustaining fisheries productivity and food security (see the figure).