How You Can Help
Join us in tracking Posidonia australis flowering and fruiting by taking part in any of the following activities:
- Fishing trips – Keep an eye out while boating or casting a line in estuaries with known Posidonia meadows.
- Snorkeling or diving – If you're in the water, especially with the Underwater Research Group or your local dive community, take a closer look at the seagrass beneath you.
- Beach walks – Washed-up seagrass can carry important clues. Flowering shoots, fruits and even seeds may drift ashore during the season.
Join our Facebook group to stay updated on events, community surveys, and guided activities happening near you. (link)
How to Identify Posidonia australis
Posidonia australis is a long-lived seagrass that forms dense meadows in shallow, sheltered estuaries and coastal lakes in NSW. It typically grows on sandy to silty sediments in clear waters between 0.5 and 5 metres deep, depending on light availability.
Key features to help you identify it:
- Long, flat leaves: Typically 10-50 cm in length but can exceed 1 metre; 5-12 mm wide. Leaves often have visible veins and may be covered with algae or epiphytes.
- Clumping growth: Leaves grow in clumps (known as shoots) from thick, horizontal rhizomes anchored in the sediment.
- Dense meadows: Unlike other seagrasses, Posidonia often forms continuous, lush beds that stabilize the seabed and support diverse marine life.
It can sometimes be confused with Zostera, which has shorter, narrower leaves and grows in sparser patches.
What to Look For – Flowering & Fruiting (show images of the different stages)
Posidonia australis typically begins flowering in August, with reproductive structures visible through spring and early summer. Here's what to look out for across the different stages:
- Early Budding Stage: Look for small, green, bean-like buds tucked between the leaf shoots at the base of the plant. These are the first signs of developing inflorescences (flowering structures).
- Spikes Emerging: As development progresses, spikes will emerge vertically from the flowering shoot. Each spike holds multiple tiny flowers, which are arranged along a central axis. Unlike many plants, Posidonia flowers are adapted for underwater pollination.
- Pollination Stage: You may see freshly opened flowers underwater. These can appear white or pale with a reddish or pinkish hue, especially around the anthers (pollen-producing structures). Some flowers may release threads of pollen, which drift in the water column to reach nearby female flowers.
- Fruiting: If pollination is successful, the flowers develop into oval, green fruits-often described as looking like small green bananas or olives. These may remain attached to the shoot or break off and float, sometimes washing up on beaches.
- Seeds: Inside each mature fruit is a single large seed. These seeds are negatively buoyant and sink to the seabed, where they can germinate and potentially establish new plants under suitable conditions.
Where to Look for Posidonia
Not sure where to find a meadow near you?
Use the DPI Fisheries NSW Spatial Viewer or visit our Resources page for a step-by-step guide on how to explore known Posidonia australis meadows across the NSW coast.
Focus on:
- Shallow, sheltered estuaries and coastal lakes
- Areas with sandy or silty bottoms
- Places with clear water and good light penetration
We also recommend checking our Sightings Map to see where flowers or fruits have already been recorded this season.
Tip: The best time to search is when the tide is dropping, around mid-tide—fresh fragments are more likely to be exposed along the shoreline.
Still not sure where to go? Feel free to reach out via our Contact Us page—we’re happy to help!
Submitting a Sighting
Understanding when and where Posidonia meadows are flowering and producing viable seeds is crucial. If we can identify those meadows, we can collect seeds and grow them in aquaria to support large-scale restoration efforts across NSW and beyond.
If you spot Posidonia flowers or fruit, we'd love to hear from you!
Here's what to do:
- Take clear photos of the plant
- Ideally from multiple angles (front and back)
- Use a contrasting background like sand or your hand to highlight key features
Note environmental details:
- Location (GPS or nearby landmark)
- Tide level
- Water temperature (if possible)
- Depth and habitat type
Upload your observations directly to our [Sightings page] (Button)
If you come across multiple plants or a range of flowering/fruiting stages, feel free to include them all in one submission. Just let us know:
- Roughly how many you saw
- What stages they were at
- And include a few clear photos of different examples
You're also welcome to submit again if you visit another site or return later the same day!
