Below the surface
Transport for NSW is working with experts from the University of NSW, Sydney Institute of Marine Science (SIMS), and local Gamay Rangers to support endangered species Posidonia australis seagrass and White’s Seahorse through restoration, research and improved habitats in Kamay (Botany Bay).
Our plan to protect these important species
While the Kamay wharves were designed to avoid as many impacts as possible, construction and operation activities have some impact on seagrass, including Posidonia at the Kurnell wharf site.
We’ve developed a plan called the Marine Biodiversity Offset Strategy (MBOS) which sets out how we are managing project impacts through activities such as:
- restoring Posidonia australis seagrass to create more habitat than is expected to be directly affected
- converting chain moorings to seagrass friendly moorings to benefit Posidonia and Zostera seagrass
- providing artificial habitat (seahorse hotels) for endangered White’s Seahorse
- supporting research into seagrass rehabilitation.
We have a program of regular, long-term monitoring to help track progress and gather useful data to inform future Posidonia restoration projects in Australia.
An MBOS Implementation Reference Panel is overseeing the implementation of the MBOS which will be updated as required.
UNSW
Seagrass superpowers
- Store up to four times more carbon than terrestrial rainforests
- Provide habitat and nurseries for fish and crabs
- Improve water quality
- Help reduce coastal erosion
- Hold cultural significance for Aboriginal communities, who have long used seagrasses in multiple ways, including for clothing, basket weaving, medicinal purposes and in cultural ceremonies
What is Posidonia australis?
Posidonia australis (pronounced ‘Pos-ee-doe-nee-ah, Os-trah-lees’) is a slow-growing seagrass found along southern Australia, including in 17 estuaries along the east coast of NSW.
In NSW, Posidonia likes to live in shallow, sheltered bays, estuaries, and coastal lakes. Its leaves are bright green and strap-like (about 1 cm wide) and can grow to over 80 cm long. As much as 90 percent of the mass of the plant may be in the underground rhizome/roots. This is part of what makes seagrasses different to seaweeds; seagrasses are vascular plants that have roots, leaves, flowers and fruits. In contrast, seaweeds are a type of algae, which are evolutionarily simpler organisms and lack a vascular system (the internal transport system for nutrients and fluids).
There are about 70 species of seagrass world-wide. Seagrasses are one of the world’s oldest flowering plants, and have adapted to live fully submerged underwater. You may have heard seagrasses referred to as the ‘lungs of the ocean’, that’s because as they photosynthesise, they produce oxygen while also capturing and storing large amounts of carbon. Seagrasses also help to prevent erosion and provide shelter for many aquatic animals, including White’s Seahorse in the Sydney region.
In Kamay (Botany Bay), you can find seagrass species Zostera (eelgrass), Halophila (paddleweed) and Posidonia.
Increased human activity in coastal areas has had a major impact on Posidonia populations, although natural causes, such as storm events, can also lead to declines.
Unlike fast-growing seagrasses like Halophila and Zostera, Posidonia grows slowly and is particularly sensitive to disturbances, making recovery more difficult.
Posidonia is currently listed as endangered in six NSW estuaries, including Kamay.
To learn more about Posidonia, visit the Department of Primary Industries and Regional Development and search ‘Posidonia australis’.
Steps to Posidonia seagrass restoration
Planning
During 2021 and 2022, marine ecologists surveyed and mapped the project impact area to understand Posidonia growth patterns. They also assessed the nearby Posidonia meadow at Kurnell to identify the best sites for rehabilitation. Some of these sites include areas where damaged sections of the meadow (known as ‘scars’) can be repaired to support natural recovery.
Harvesting and replanting
Harvesting Posidonia from the project impact area at Kurnell took place in 2023.
Scientific divers carefully removed plants from the seabed, taking care to protect the rhizomes (root structures). The seagrass was then replanted into nearby rehabilitation sites.
In some locations, biodegradable jute matting was used to help anchor the plants in the seafloor while they established.
Around 13,000 seagrass shoots were relocated and the area mapped to support ongoing monitoring.
Replanting naturally detached Posidonia fragments
During storm event sand strong weather conditions, Posidonia plants can naturally break away from meadows and wash ashore. The Gamay Rangers and UNSW Scientists collect suitable naturally detached fragments from beaches around Kamay and store them in specialised holding tanks. These fragments are then replanted into the rehabilitation sites at Kurnell to support restoration efforts.
Monitoring
Long-term monitoring is a critical part of the restoration program.
UNSW Scientists monitor factors such as:
- the extent of the seagrass area
- plant density and condition
- function of the seagrass rehabilitation areas
These results are compared with existing ‘reference’ sites to measure progress of the rehabilitation efforts over time.
Advanced technology, including the underwater Hullbot robot, is used to create 3D model images to show visual changes in the rehabilitation sites over time.
A ten-year monitoring program is underway, with additional post-storm monitoring undertaken where needed to assess any naturally occurring impacts. Monitoring reports are available on the project documents webpage.
No anchoring in Posidonia protection zone
Seagrass in shallow areas such as Botany Bay, Kurnell, is vulnerable to damage from boat anchors and propellers. To help protect the seagrass rehabilitation sites at Kurnell, a ‘no-anchoring’ zone is in place. Please follow signage and yellow marker buoys. We also encourage boaters to lift propellers when boating in shallow depths around seagrass.
Map of seagrass protection zone
Protecting seagrass with more environmentally friendly moorings
To further support Posidonia recovery, we’re upgrading traditional boat moorings and navigational aids to designs that are less harmful to seagrass. As part of this work, we plan to convert or relocate at least 20 standard boat moorings and marine navigational aids, with a stretch target of achieving 30 sites.
Traditional style boat mooring and navigational aids have thick metal chains that can drag across the seafloor and damage seagrass beds. As part of our work, we’ll be replacing the chain section with an elastic, buoyant line, that stay lifted off the seabed and reduce contact with the seafloor (called an Environmentally Friendly Mooring, or EFM).
When it comes to the marine navigational aids (also referred to as AToNs), such as navigational marker buoys, we will either convert them to an EFM style design, or into a fixed pylon.
We are planning to roll out these improvements on Transport-owned moorings between Narooma and Port Stephens, including sites in Kamay. These locations were chosen because they have the greatest potential to contribute towards recovery of known seagrass scars including key sites in endangered Posidonia seagrass.
This work will also help us learn more about this technology and its maintenance, share lessons learnt, and support broader seagrass restoration efforts across NSW.
You can also read about Transport’s Environmentally Friendly Mooring Research Program.
Homes for seahorses in Kamay
As part of our MBOS, artificial habitats, known as seahorse hotels, have been installed to support endangered White’s Seahorse.
White’s Seahorse (Hippocampus whitei) is a medium-sized species found along Australia’s east coast, from Hervey Bay in South-East Queensland to Sussex Inlet in the mid-New South Wales coast.
They are known to live in seagrasses, including Posidonia australis. Several have been spotted during our project dive inspections in Kamay.
We collaborated with NSW Department of Primary Industries and Regional Development Fisheries, seahorse experts from the Sydney Institute for Marine Science (SIMS), Gamay Rangers and the MBOS Implementation Reference Panel to develop an artificial habitat implementation plan, which includes a five-year monitoring program.
What is a seahorse hotel?
Seahorse hotels are purpose-built metal units that start as artificial habitats, but are rapidly encrusted by algae, sponges and corals once placed in the marine environment (this is called biofouling).
Over time, the marine growth forms a new scaffolding and structure while the metal corrodes leaving a new natural habitat behind and perfect homes for Syngnathids (the family of fish that include seahorses, seadragons, pipehorses or pipefish).
This is not the first-time seahorse hotels have been used – you can read more about how these simple, yet effective creations are being used in NSW on these websites:
- Department of Primary Industries and Regional Development – seahorse hotels and captive breeding program
- Sydney Institute of Marine Science – The Sydney Seahorse Project
- UNSW – Operation Posidonia seahorse hotels
UNSW
Where are the seahorse hotels located?
In July 2025, we installed 60 seahorse hotels across Kamay at:
- Frenchmans Bay and Congwong Bay on the La Perouse side
- Inscription Point and Silver Beach on the Kurnell side.
The site selection was based on expert advice from Sydney Institute of Marine Science (SIMS) and consultation with multiple stakeholders including DPIRD Fisheries, Port Authority NSW, and the MBOS Panel.
Some of the key considerations included:
- known presence of White’s Seahorse
- proximity to existing habitat such as seagrass or sponges
- suitable marine conditions (such as water depth, swell and exposure)
- local cultural knowledge shared by the Gamay Rangers.
Supporting seahorse populations
And in March 2026, we joined SIMS, the University of Technology, Sydney, DPIRD Fisheries and the Gamay Rangers as part of their Sydney Seahorse Project to release 200 captive-bred juvenile White’s Seahorses onto some of our seahorse hotels and nearby seagrass in Kamay.
Underwater views of SIMS White’s Seahorses being released onto seahorse hotels in Kamay, March 2026. Image credit: Woody Spark.
Monitoring and tracking success
A dedicated monitoring program is in place to assess the effectiveness of seahorse hotels over time.
Marine specialists monitor factors such as:
- marine growth on the hotels over time
- the presence of wild and released White’s Seahorse using the hotels, to learn more about the health and size of the local population
- overall use by other seahorse and marine species.
Monitoring started in August 2025 and will continue as part of a five-year program, with annual reports published on the project webpage.
Ripple effects
In addition to creating a net gain of White’s Seahorse habitat, this work provides a range of broader environmental, research, and community benefits, including:
- supporting captive breeding and release programs by providing suitable release sites
- providing habitat that benefits a range of other marine species including other Syngnathiformes (such as seadragons, piepefish and pipehorses)
- contributing to research that addresses key knowledge gaps for White’s Seahorse, including improving understanding of size, health and distribution of local populations
- creating opportunities for community members to contribute to scientific research by recording and sharing seahorse sightings through established citizen science platforms
- collaborating on the monitoring program with Gamay Rangers to support ongoing connections to Sea Country and building on skills and experience in marine ecology fieldwork.
Call for community scientists
You can play an important role in supporting scientific studies by sharing your own observations. Our marine specialists can’t be in the field every day, so your sightings can provide valuable information that contributes to ongoing research and conservation work.
We encourage you to record observations within Kamay (Botany Bay) area, including:
- Seahorses: Submit sightings to the Sydney Seahorse Project through the citizen science tool iNaturalist. More information about this work is available on the SIMS website.
- Seagrass flowers and fruit (seeds): Report observations in the water or along the shoreline to the Seeds of the Sea project, part of the broader Operation Posidonia program.
