Oyster Reef Restoration
Construction of the largest oyster reef restoration project outside the U.S.A. started in July 2017 in the coastal waters of Gulf St Vincent, 1 km offshore from Ardrossan on the Yorke Peninsula.
This ambitious project aims to restore 20 hectares of oyster reef where historic reefs once thrived. It is the first attempt at large-scale oyster restoration in the southern hemisphere, a pioneering project that will hopefully provide the blueprint for many future restorations around Australia and the world.
This A$4.2-million project is being constructed in two phases:
- the first phase is the 4-hectare trial being built by Primary Industries and Regions South Australia, and;
- the second phase will see the reef expand to 20 hectares, led by The Nature Conservancy.
The construction of the 20 hectare reef should be complete by December 2018, which will see 18,000 tonne of limestone laid on the seabed, providing the foundations for oyster growth. While the construction of the limestone reef is relatively straight forward, the restoration of flat oyster populations at this scale is not, with many unanswered questions.
Seafloor at the restoration site:
oyster reefs once thrived here
The University of Adelaide is conducting research to understand the threats posed to oyster restoration, and how we can maximise the survivorship, growth and recruitment of oysters over time.
So how do you build an oyster reef?
Selection of an appropriate site for restoration is key, and this was largely informed the re-discovery that enormous oyster reefs once thrived in Gulf St. Vincent. Not disturbing other biodiverse habitat (i.e. seagrass) was important for the site selection, with pre-construction dives confirming that few organisms grow on the sandy seafloor chosen for restoration.
Locally sourced limestone is being carefully deployed on the seabed in a patchwork of individual (~5-7 m long) reefs. When complete, these reefs will cover approximately 4% of the 20 hectare seafloor. This mosaic of closely located (~10 m) reef patches will allow oyster larvae to disperse between the reefs once breeding populations are established, while providing a diversity of habitat types that will provide more homes to a greater range of species.
Limestone being deployed from a barge for a trial reef in Victoria
The first oysters, 7 million babies, will be deployed on the reef in October 2017.
Because there are very few flat oysters in the wild, these first oysters will be spawned in hatcheries and allowed to settle on the shells of dead oysters collected from local oyster farms. The dead shells will be placed in a tub full of oyster larvae, and as they prepare to settle down for their stationary lives the larvae “smell” other oysters which indicate a good place to settle. The seeded oyster shells will then be planted on the limestone reef, and over time the baby oysters will grow and cement together with other oysters, forming the complex habitat that is such a haven to other species.
After three years these first oysters will be reproducing, and with time natural recruitment will be the primary means of oyster colonisation, though many more artificial plantings will be required before a sufficiently large population is achieved.