Operation Posidonia

Giulia Ferretto

UNIVERSITY OF NEW SOUTH WALES

Posidonia australis forms highly productive meadows in the southern half of Australia, from Wallis Lake in New South Wales to Shark Bay in Western Australia. In New South Wales Posidonia meadows are found mostly in shallow and sheltered bays, which are also preferred areas for humans to live. Increased coastal development and pollution has led to major declines of Posidonia over the last few decades.

The declines of Posidonia meadows in the central parts of New South Wales (NSW) have been so severe that six meadows have been formally listed as ‘endangered’ by the NSW government in 2012. The Australian Commonwealth Government subsequently listed Posidonia meadows as ‘threatened ecological communities’ in 2015 (EPBC Act, 1999). Unfortunately, there is a real risk that this species may become locally extinct from some of these estuaries within the next 15 years unless new conservation actions reverse current trends. To reverse this decline and prevent further losses, there are now strict regulations that limit coastal development near seagrass meadows, and water quality has greatly improved in the last couple of decades.

There are still some human activities that continue to be a problem and are still leading to the decline of Posidonia in some estuaries. Boat moorings are one of the most obvious current disturbances to seagrass habitats, as the sheltered bays where this seagrass naturally thrives are also the most ideal locations for people to moor their boats. The problem with traditional swing moorings, is that they have a heavy chain that scours the seafloor, removing seagrass shoots and associated marine life. This process causes the formation of sandy bare patches that fragment the meadow and over time, as the mooring scars get larger, bare patches start to merge, leading to more Posidonia losses. Alternative mooring designs now exist (so-called environmentally friendly moorings or EFMs), that do not have components dragging along the seafloor. Large scale transition to the EFMs could prevent ongoing damage to Posidonia. However, the natural revegetation of bare patches by Posidonia can still take decades, especially after large mooring scars have developed.

Operation Posidonia is promoting the recovery of Posidonia by combining removal of swing moorings (and replacement with EFMs) and restoration by transplanting. One of the main logistical problems when restoring an endangered plant is obtaining the material for the revegetation, as taking cuttings from undisturbed vegetation could perpetuate the vulnerability of the species. The main innovation of Operation Posidonia is that we are using naturally-detached fragments of Posidonia australis that have washed ashore. These are collected by citizen scientists as our source of plants for the restoration. If fragments are still living and have a rhizome structure for anchoring and growth, they can be used for restoration.

Our restoration project is reversing some of that boat mooring damage on seagrass meadows, while also increasing environmental awareness in local communities. Our research team includes scientists from the University of New South Wales (UNSW), the Sydney Institute of Marine Science (SIMS), the NSW Department of Primary Industries (NSW DPI) and collaborators from the University of Western Australia (UWA). We have been restoring Posidonia in mooring scars in Port Stephens, the second most impacted estuary by boat moorings in NSW.

Operation Posidonia was launched in 2018 in Port Stephens to engage local communities.  The ‘Storm Squad’, i.e. our ‘army’ of citizen scientist volunteers, started collecting naturally detached Posidonia fragments washed up on the beach after storms, strong winds and high tides in October 2018.

Over the first two years we had over 1500 Posidonia fragments donated by citizen scientists. We used these fragments to revegetate 10 mooring scars between 2019 and 2020. After receiving fragments from our ‘Storm Squad’, we temporally stored them in large outdoor tanks at the Port Stephens Fisheries Institute until we had enough for restoration efforts.

We found that fragments planted in winter survived better that those planted in summer, with some replanted areas reaching 70% survival after one year. This is a great result considering that otherwise those fragments wouldn’t have had another chance than drying up in the sun. Most of the transplanted fragments produced new shoots after only a few months, showing that they are beginning to re-establish on their own and expand in nearby areas. 

The project in Port Stephens was a ‘proof of concept’ to see whether this method of restoration works. We have now demonstrated that this can be effective and we are now expanding Operation Posidonia in Lake Macquarie and Botany Bay, two of the estuaries where Posidonia australis is formally listed as endangered in NSW.