They may not have the visual drama of coral reefs or the towering grandeur of kelp forests, but seagrass meadows are among the most ecologically and economically important habitats in the ocean. Found in shallow coastal waters on every continent except Antarctica, these flowering plants — true plants, not algae — provide a suite of ecosystem services that rival any habitat on the planet.
What Are Seagrasses?
Seagrasses are the only flowering plants that live fully submerged in the marine environment. Unlike seaweeds, they have true roots, stems, and leaves. They reproduce both sexually, via flowers and seeds, and asexually, through horizontal rhizomes that spread across the sediment. Australia is home to over 30 seagrass species — the highest diversity of any region in the world — and supports some of the largest seagrass meadows globally, including those in Shark Bay, Western Australia, a UNESCO World Heritage Site.
Ecological Services
Seagrass meadows support food webs by providing primary productivity and organic matter. They are critical feeding grounds for dugongs, green turtles, and numerous fish species. Their dense root and rhizome networks stabilise sediment, reducing turbidity and improving water clarity. They also cycle nutrients, removing excess nitrogen and phosphorus from the water column and locking it into plant biomass and sediment.
Blue Carbon Powerhouses
Seagrasses are disproportionately important carbon sinks relative to their area. Although they cover only 0.1 percent of the seafloor, they are estimated to account for up to 18 percent of oceanic carbon burial. Carbon stored in seagrass sediments can remain locked away for centuries or millennia, making seagrass conservation a highly cost-effective climate mitigation strategy.
The Scale of Seagrass Loss
Globally, an estimated 29 percent of the world’s seagrass area has been lost since the late 19th century. In Australia, disturbance events including cyclones, floods delivering sediment loads, and warming water temperatures have caused significant localised losses. The impacts of reduced light availability — whether from algal blooms, sediment run-off, or coastal development — are a leading driver of decline.
Restoration and the Role of Substrate
Seagrass restoration typically involves transplanting shoots, seed dispersal, or the deployment of purpose-designed anchoring substrates to help seedlings establish in dynamic sediment environments. Stable, biologically receptive substrates can dramatically improve seedling survival rates, particularly in areas with high wave or current energy. This is an area where biosubstrate engineering has significant potential to contribute to restoration outcomes.
Key resources for seagrass science and conservation: seagrasswatch.org, csiro.au, environment.gov.au.
