a ribbon in the meadows Southern Strapweed

Hear all about it!

Posidonia australis grows in shallow coastal waters which are protected from high wave energy. It is found in water depths from 1-15 m. It can even grow in depths of 22 m in clear, non-polluted water.

Despite their big leaves, 90% of the Posidonia australis plant actually exists in root form in the sandy or silty seabed. Nearer the seabed, there are more leaf blades closer together. Further up, these blades thin out creating an open canopy.

Most of the animals that live in seagrass meadows do not eat the seagrass itself. Rather, they eat the algae that grow on it, or prey on each other. The exception to this is the Green Turtle and Leatherjacket fish which feeds directly on seagrass like the Posidonia australis.

This seagrass species also produces large green fruits which can be found on the beach between November and January.

Threats include; human impact caused by physical damage from dredging, anchors and motors, pollution and increased nutrient levels in water from incorrect sewage disposal. Natural threats from storm damage and reductions in light from the eutrophication (breakdown of nutrients) process.

Where you can find a Southern Strapweed

Conservation Status

Listed as Near Threatened under ICUN (2014). Some parts of Rottnest’ seagrass meadows are included the Marine Sanctuary Zones shown in the Rottnest Island Marine Management Strategy 2007.
  • Extinct
  • Extinct in Wild
  • Critically Endangered
  • Endangered
  • Vulnerable
  • Near Threatened
  • Least Concerned

Help keep Rottnest's marine environment healthy

  • Do anchor only in sandy areas of water
  • Do snorkel and enjoy the marine environment
  • Do take litter with you or use bins provided