Reviving shellfish reef socio-ecological histories for modern management and restoration

Significant changes in the exploitation and management of coastal resources over the past three centuries have coincided with global declines in natural ecosystems and their socio-ecological services. Shellfish ecosystems have suffered enormous declines across temperate and tropical coastal ecosystems worldwide. Efforts to restore shellfish reefs have increased due to growing awareness of their loss and ecological importance. However, successful conservation requires robust knowledge of ecosystem characteristics, stressors, and socio-cultural support. In turn, this information can underpin coastal management, restoration targets, and help foster stakeholder support. Establishing evidence-bases can, however, be difficult due to ecological regime shifts and fragmented knowledge sources. Here, data from diverse literature records were integrated to synthesise South Australia's past shellfish ecosystem distribution, management, and socio-ecological services. Specifically, we contrasted available accounts of flat oyster (Ostrea angasi), razor clam (Pinna bicolor), and hammer oyster (Malleus meridianus) ecosystems, and their co-occurrence. Based on historical records, we documented 140 potential shellfish reef locations, with these ecosystems previously characterising >2630 square kilometres of South Australia's coastal waters. This review also collates literature concerning shellfish harvesting, both prior to, and following European colonial influence. We estimate that over 43 million flat oysters were commercially harvested statewide between 1849 and 1915, prior to their functional extinction by the 1940s. Flat oyster reef declines motivated South Australia's earliest fisheries legislation (est. 1853) and marine restoration efforts, including fishery closures (est. 1875), shellfish translocation (est. 1887), and marine reserves (est. 1912). Historical records indicate that shellfish reefs, of multiple ecosystem-forming bivalves, diminished over the past ≈200 years due to cumulative impacts of destructive benthic fishing practices, environmental stressors, and changes in marine resource management. By reconstructing past shellfish reef distributions and socio-cultural connections, this review identifies evidence-based opportunities and key knowledge gaps to guide future research and management efforts.