What Is Seagrass?
Seagrass is not seaweed. It's a flowering plant — one of the very few that can live fully submerged in saltwater. Found in shallow coastal waters on every continent except Antarctica, seagrass forms dense underwater meadows that look, from above, like fields of waving green grass.
Despite covering less than 0.2% of the ocean floor, these meadows punch far above their weight in ecological importance.
Why Seagrass Meadows Matter
Carbon Capture
Seagrass meadows are extraordinary carbon sinks. They can sequester carbon up to 35 times faster than tropical rainforests, storing it in both their leaves and the sediment beneath — where it can remain locked away for millennia. This makes seagrass restoration one of the most promising nature-based climate solutions available to us.
Nursery Habitat for Marine Life
The dense canopy of seagrass provides shelter, feeding grounds, and breeding habitat for an enormous range of species. Many commercially important fish — including sea bass, mullet, and various flatfish — spend critical juvenile stages in seagrass beds. Without these nurseries, fish populations in surrounding waters decline sharply.
Water Quality
Seagrass acts as a natural filter, trapping sediment and absorbing excess nutrients from agricultural runoff and coastal development. Healthy seagrass beds are strongly associated with clearer, cleaner coastal water.
Coastal Protection
The root systems of seagrass stabilise sediment and reduce the energy of incoming waves, helping to protect coastlines from erosion — a function that becomes increasingly valuable as sea levels rise.
What Lives in a Seagrass Meadow?
- Seahorses: Use seagrass blades to anchor themselves with their prehensile tails
- Sea turtles: Seagrass is a primary food source for green turtles
- Dugongs and manatees: Graze extensively on seagrass and are deeply dependent on healthy meadows
- Pipefish: Masters of camouflage among the grass blades
- Wading birds: Feed on the invertebrates that live at the sediment surface
The Threats Seagrass Faces
Seagrass meadows have declined significantly over the past century. The primary culprits are:
- Water quality degradation: Nutrient pollution causes algal blooms that block sunlight, starving seagrass of the light it needs to photosynthesise.
- Physical disturbance: Boat propellers, dredging, and coastal development can destroy meadows that took decades to establish.
- Rising water temperatures: Climate change is pushing some seagrass species beyond their thermal tolerance, particularly in tropical and subtropical regions.
- Disease: Wasting disease, caused by a marine slime mould, has historically devastated large areas of seagrass in the North Atlantic.
Restoration Efforts
Encouragingly, seagrass restoration is a growing field. Projects in the UK, Australia, and the United States have demonstrated that with appropriate seed collection, improved water quality, and community involvement, meadows can be re-established in areas where they were lost. The Virginia Coast Reserve seagrass restoration programme in the USA is often cited as one of the most successful large-scale coastal habitat restoration projects in history.
How You Can Help
- Drop anchor carefully in coastal areas — use designated moorings where available
- Support organisations working on seagrass restoration and monitoring
- Reduce fertiliser and chemical runoff from gardens near waterways
- Learn to identify seagrass when snorkelling or diving — and report healthy beds to citizen science platforms
The meadows beneath the surface may be invisible from the shore, but the health of our bays depends on them. They deserve far more of our attention.