Conservation status of oyster reef ecosystem of Southern and Eastern Australia

Reef ecosystems all over the world are in decline and managers urgently need information that can assess management interventions and set national conservation targets. We assess the conservation status and risk of ecosystem collapse for the Oyster Reef Ecosystem of Southern and Eastern Australia, which comprises two community sub-types established by Saccostrea glomerata (Sydney rock oyster) and Ostrea angasi (Australian flat oyster), consistent with the IUCN Red List of Ecosystems risk assessment process. We established: (i) key aspects of the ecosystem including: ecological description, biological characteristics, condition and collapse thresholds, natural and threatening processes; (ii) previous and current extent of occurrence and current area of occupancy; and (iii) its likelihood of collapse within the next 50e100 years. The most severe risk rating occurred for Criterion A: Reduction in Extent (since 1750) and Criterion D: Disruption of biotic processes (since 1750), although assessment varied from Least Concern to Critically Endangered amongst the four criteria assessed. Our overall assessment ranks the risk of collapse for the ecosystem (including both community sub-types) as Critically Endangered with a high degree of confidence. Our results suggest the need for rapid intervention to protect remaining reefs and undertake restoration at suitable sites. Several restoration projects have already demonstrated this is feasible, and Australia is well equipped with government policies and regulatory mechanisms to support the future conservation and recovery of temperate oyster ecosystems

The value and opportunity of restoring Australia's lost rock oyster reefs

Recognizing the historical loss of habitats and the value and opportunities for their recovery is essential for mobilizing habitat restoration as a solution for managing ecosystem function. Just 200 years ago, Sydney rock oysters (Saccostrea glomerata) formed extensive reef ecosystems along Australia's temperate east coast, but a century of intensive harvest and coastal change now confines S. glomerata to encrusting the hard-intertidal surfaces of sheltered coastal waters. Despite the lack of natural reef recovery, there appears enormous potential for the restoration of intertidal S. glomerata ecosystems across Australia's east coast, with large anticipated benefits to water quality, shoreline protection, and coastal productivity. Yet, no subtidal reefs remain and the potential for subtidal restoration is a critical knowledge gap. Here, we synthesize historical, ecological, and aquaculture literature to describe a reference system for the traits of S. glomerata reefs to inform restoration targets, and outline the barriers to, and opportunities and methods for, their restoration. These reefs support extremely biodiverse and productive communities and can ameliorate the environmental stress experienced by associated communities. Rock oyster restoration, therefore, provides an ecosystem-based strategy for assisting the adaptation of marine biodiversity to a changing climate and intensive human encroachment. Though an estimated 92% of S. glomerata ecosystems are lost, there remains great potential to restore these valuable and resilient ecosystems