About Posidonia australis
Posidonia australis is a species of seagrass that occurs in the southern half of Australia. It occurs in 17 estuaries along the east coast of New South Wales from Wallis Lake to Twofold Bay near the New South Wales/Victorian border.
Six locations within New South Wales (Port Hacking, Botany Bay, Sydney Harbour, Pittwater, Brisbane Waters and Lake Macquarie) have suffered significant population decline and have been listed as endangered populations.
The species can grow in coarse sandy to fine silty sediments between the low tide line and approximately 10 m depth. It may also occur in deeper water if water clarity is good. It can form large, dense stands (called meadows), and is also often found mixed with other species of seagrass such as Zostera (eelgrass) and Halophila (paddleweed).
Posidonia australis is important because:
- It supports a diverse range of fauna, providing habitat, shelter and food. This includes other protected and threatened species such as the White's Seahorse, Little Penguins, Green Turtles, pipefish and seadragons.
- It also provides nursery habitat and feeding grounds for commercially and recreationally important fish species such as bream, sea mullet, leatherjacket, mullet and garfish.
- Protects water quality by filtering the water and removing and recycling nutrients.
- Stabilises sediment on the seabed.
- Improves air quality by taking carbon dioxide gas out of the water and releasing oxygen. The leaves use the carbon to grow and are eventually buried in the sand when they die. This is an example of "blue carbon" - a captive of the seabed and no longer a greenhouse gas in the atmosphere.
- Seagrasses can bury carbon at a rate 35 times faster than tropical rainforests!
Why are some populations of Posidonia australis endangered?
The small and fragmented endangered populations of Posidonia australis are susceptible to many ongoing pressures including:
- The construction of foreshore structures such as jetties, pontoons and berthing areas which cause shading and loss of seagrass.
- Dredging.
- Damage from anchors, boat propellers, moorings and other boating related activities.
- Increased sediment entering waterways which can smother seagrass and block light.
- Trampling of seagrass beds due to wading by humans and domestic animals.
- Extreme storm events can dislodge large areas of Posidonia. Stormwater discharges can also change water quality and salinity levels.
- Climate change.
Posidonia australis is extremely slow to regenerate, taking up to 50 years to regrow a 1m2 area.
An endangered White's Seahorse on Posidonia australis. A scour through a Posidonia australis meadow. Photos: David Harasti
Information: NSW DPI
Environmentally Friendly Moorings
A key part of Project Restore is the replacement of up to 16 swing moorings to environmentally friendly moorings. This is an exciting opportunity for mooring owners to be a part of Project Restore and help restore Sydney Harbour’s degraded seascapes.
Swing chain mooring’s are the most common mooring technology and widespread use is leading to ongoing threats to seagrass. As the chain drags along the seafloor it destroys the seagrass beds and leaves a mooring scar on the seafloor. Environmentally Friendly Moorings use neutrally buoyant technology that removes the impact on the seafloor while still providing a robust anchoring system.
As part of Project Restore, and in collaboration with Transport for New South Wales (TfNSW), we are offering sponsorship of up to 16 mooring owners in support of replacement of block-and-chain moorings to Environmentally Friendly Moorings.
This sponsorship covers all costs involved in removing existing moorings and buoys and replacing with the Environmentally Friendly units. Additionally, the mooring servicing fees for the duration of the project (until 2026) will be covered by Project Restore.
If you’re a mooring owner or want to find out more, register your interest in the program by emailing project.restore@sims.org.au or view the information PDF here.
More on SIMS Webpage: projectrestore.sims.org.au/get-involved#seagrass-collection
Operation Crayweed: Commenced with Crayweed from Palm Beach
This is the second type of Palm Beach seaweed that has been collected to help restore other areas. In 2014 UNSW and SIMS began collecting Crayweed from Palm Beach to help return other places to how they once were.
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- Bringing Sea Horses and Kelp Forests Back To World's Most Iconic Harbour: Seabirds To Seascapes - August 2022
- Seaweed Forests Festival Podcast Launch: Dive Deep Online Into How YOU Can Help Our Oceans! - August 2021
- Seaweed Forests Festival, Manly: April 9th - May 9th, 2021 - March 2021
- Under The Sea: Weird and Wonderful Creatures To Look For While Snorkelling This Summer + Operation Crayweed Newport Has Commenced - 2021 1st Update - January 2021
- ‘Operation Crayweed’ Manly: Engaging The Manly Community In Restoring Manly’s Lost Underwater Forests - Newport and Freshwater to come! - May 2020
- Living Seawall Tiles Installed On Sydney Harbour Are Turning The Habitat Tide - November 2018
- Operation Crayweed Update: Success As North Bondi Restoration Works Produce Next Generation Of Crayweed - Also This Week: Green Globe Award For UNSW SIMs Operation Crayweed Project - October 2017
- Artists, Scientists and Children Celebrate Restoration Of Underwater Forests - October 2016
- Palm Beach Seaweed Contributes To Reef Restoration - Bald Reef Gets New Growth With Seaweed Transplant - January 2014
