Seeds of the Sea
Tracking the flowering and fruiting of Posidonia australis.
Seeds of the Sea is a UNSW-led citizen science and research project that’s uncovering when and where the endangered seagrass Posidonia australis flowers and produces seeds across New South Wales.
With help from community members, Indigenous Rangers, divers, and scientists, the project is building the first statewide dataset on seagrass reproduction — crucial knowledge to guide future seed-based restoration and help bring back lost meadows.
Why it matters
Posidonia australis meadows are disappearing from our estuaries — particularly along urbanised coastlines such as Sydney, Pittwater, Gamay Botany Bay, and Lake Macquarie. These underwater forests play a crucial role in coastal health: they stabilise sediments, improve water clarity, capture carbon, and provide nursery habitat for fish, rays, and seahorses.
In New South Wales, Posidonia australis is now listed as endangered in six estuaries due to the widespread loss of these meadows. They are increasingly threatened by coastal development, dredging, poor water quality, boat moorings, and climate-driven marine heatwaves. Once damaged, Posidonia meadows recover extremely slowly — often taking decades to return naturally.
Understanding when and where flowering occurs is essential to bringing them back. Sexual reproduction through seeds provides the genetic diversity needed for resilience and adaptation, helping ensure restored meadows are strong enough to survive future change. By identifying flowering hotspots, we can collect seeds and reintroduce locally adapted genetic material to estuaries where meadows have been lost.
Where to find it
Posidonia australis grows in sheltered estuaries and coastal lakes along the NSW coast — from Wallis Lake in the north to Twofold Bay in the south. It thrives in calm, clear waters with sandy or silty seabeds, where it forms dense, long-lived meadows that stabilise the shoreline.
These are the meadows we’re watching for signs of flowering and fruiting each year.
Flowering and fruiting
Posidonia australis flowers underwater — a rare and remarkable process. Each flowering shoot can produce several small flowers that are pollinated by ocean currents rather than wind or insects. When fertilised, the flowers form olive-sized green fruits that float at the surface before releasing seedlings that sink and take root in the seabed.
Understanding this cycle helps scientists and community members identify when and where seed collection is possible, building the foundation for large-scale seagrass restoration.
The flowering and fruiting stages of Posidonia australis:
Citizen science
You can help by reporting sightings of flowering or fruiting Posidonia australis — whether you’re diving, snorkeling, or walking along the beach.
Visit our website to learn more, explore recent sightings, or get involved in community monitoring events.
Partners
This project is a collaboration between scientists, Indigenous communities, and environmental organisations working together to protect and restore seagrass ecosystems across NSW.
In collaboration with:
Funding support
Supported by the Wettenhall Environment Trust, The Holsworth Wildlife Research Endowment, and The Ecological Society of Australia.
