Clayton Mead and Giulia Ferretto, University of NSW Sydney.

The Port Stephens estuary in New South Wales is a popular coastal playground, where the inviting, calm waters are perfect for fishing, swimming and cruising on boats. People are naturally drawn to coastal bays like this, which are rich in precious marine life. Seagrass meadows, which thrive in sheltered waters, provide habitat and food to many species. They support fisheries, capture carbon and protect shorelines. Unfortunately, as coasts are increasingly developed, seagrass meadows are declining at alarming rates. 

A striking volcanic hill, called Tomaree, stands between Port Stephens and the open ocean. The hike to its peak gives beautiful panoramic views of Shoal Bay. Peering down on the calm waters, you might notice a peculiar pattern in the seafloor. Darker areas, close to shore, are broken up by circular, sandy patches. Look a bit closer and you’ll notice many of these sandy patches are associated with a moored boat. Traditional boat moorings consist of a heavy, swinging chain that drags on the seafloor and moves with the wind and with tides, removing all the marine life in its path, including seagrass. The bare patches that create a mosaic in bays like Shoal Bay are the scars of a problem that has led to more than 130,000m2 of seagrass loss in NSW. Our restoration project is reversing some of this mooring damage, while empowering local communities to be active in marine conservation.

Introducing the mighty Posidonia australis

Posidonia australis is a large, dominant seagrass found along the entire southern coast of Australia. Posidonia is especially vulnerable to physical damage because it grows much slower than other species, taking decades to recover even when disturbances stop. Posidonia populations in six NSW estuaries are now listed as endangered by both NSW legislation and federally through the EPBC Act. While legal measures can protect Posidonia from some threats, traditional boat moorings remain a widespread feature of NSW’s coastal bays and estuaries.

All hands on deck to repair underwater meadows 

Our research team from UNSW Sydney, the NSW Department of Primary Industries, University of Western Australia and the Sydney Institute of Marine Science (SIMS) has been restoring Posidonia in Port Stephens, the second most impacted estuary by boat moorings in NSW. 

Restoration where moorings have been removed is important, but we also need a major shift in mooring practices to prevent further loss of Posidonia. Large scale transition to alternative mooring designs (so called environmentally friendly moorings or EFMs), that do not have components dragging along the seafloor, could prevent further damage to seagrasses. We tested Posidonia restoration in scars with newly installed EFMs to find out if combining restoration with a switch to EFMs is a potential solution for both boat owners and seagrass. 

Restoring Posidonia isn’t so straightforward, however, as taking donor material from healthy meadows can put declining or vulnerable populations at risk. So, we devised a creative solution – using naturally-detached Posidonia fragments that end up ashore after large storms and high tides, which if still living, may be viable for transplanting. 

We started a science communication campaign to call local Port Stephens ocean lovers to action. We called the project ‘Operation Posidonia’ and used social media and community events to invite ‘Storm Squad’ volunteers to collect beach-cast fragments of Posidonia. Volunteers drop off fragments at designated collection spots to be recovered by our team. With their help, we were able to recover sufficient fragments for the restoration, all while raising local awareness for the marine environment. The community was excited to be hands-on with conservation and collected more than 1500 Posidonia fragments over 18 months. We used the fragments to restore 10 mooring scars in Port Stephens.

Results from our restoration have just been published in Biological Conservation, led by PhD student Giulia Ferretto. Naturally-detached fragments of Posidonia are a great solution to revegetate fragmented meadows. Some restored areas showed up to 70% survival of replanted fragments after one year, and most transplanted fragments produced new shoots after only a few months, meaning the seagrass is beginning to re-establish on its own. We also learned that certain factors such as season of planting, morphological traits and sediment-stabilising techniques can affect restoration success. Excitingly, restoration under EFMs worked, and it looks like this could be a great solution for both people and seagrass after all.

What’s next for Operation Posidonia?

We recently launched Operation Posidonia in Lake Macquarie, and Botany Bay is up next. Our expansion comes with some exciting new collaborations, including with OzFish Unlimited, an organisation working to restore fish habitat for a healthier environment and better recreational fishing, and the Gamay Rangers, Australia’s first urban Indigenous Ranger group. In 2022 we’ll be restoring Posidonia alongside rehabilitation of White’s Seahorse populations across NSW. We hope to find plenty of new Storm Squad members, so watch out for opportunities to be involved! 

More information at operationposidonia.com and Follow Operation Posidonia on Facebook, Twitter and Instagram. Operation Posidonia has been supported by the NSW Government through its Environmental Trust as well as the NSW Recreational Fishing Trust.