Restoring Angasi oyster reefs: what is the endpoint ecosystem we are aiming for and how do we get there?

Three-dimensional reefs and beds created predominately by the native Angasi Oyster or Flat Oyster (Ostrea angasi) were once common across its range in Australia's southern coastal waters but were lost during the mid-late 1800s and early 1900s due to a combination of destructive fishing practices, overfishing and changes to estuarine conditions. Despite the continued presence of low densities of individuals and cessation of commercial fishing, reefs structures and their associated communities have shown little signs of natural recovery. Since 2014, a range of oyster reef restoration projects have commenced in Australia, guided by international restoration protocols that prioritise the re-establishment of the keystone species on artificial stable substrates placed in locations where natural oyster reefs have previously existed. These projects invariably need clear and realistic goals and objectives for restoration, which are aided by the use of a reference ecosystem as a model or target, for the local oyster reef ecosystem being restored, yet few reference sites exist. Reefs, established by Angasi, are absent from much or all of its geographical distribution, and the ecosystem has been poorly studied to date; hence, the application of restoration target ecosystems will largely depend on deriving a model based on historical descriptions and observation of what remains. Here, we develop an interim reference model to help set restoration objectives and recommended procedural framework for Angasi reef restoration based on available knowledge of the ecology, biology and aquaculture of the keystone species. We use the Port Phillip Bay oyster reef restoration project as a case study for using the reference model to guide interventions and evaluate the progress of recovery.