Recovering the loss of shellfish reefs, from coastal ecosystems and human memory

Oyster reefs form over extensive areas and the diversity and productivity of sheltered coasts depend on them. Due to the relatively recent population growth of coastal settlements in Australia we evaluated the collapse and... [ view full abstract ]

Oyster reefs form over extensive areas and the diversity and productivity of sheltered coasts depend on them. Due to the relatively recent population growth of coastal settlements in Australia we evaluated the collapse and extirpation of native oyster reefs (Ostrea angasi) over the course of a commercial fishery. This decline was evaluated against the contemporary ecological and policy status of O. angasi and oyster reefs, and extended to consider their future desired state. Historical records were used to quantify commercial catch of O. angasi in South Australia from European colonization, around 1836, to some of the last recorded catches in 1944 and estimates of catch and effort to map their past distribution and assess oyster abundance over 180 years. Historically oyster reefs extended across more than 1,500 km of coastline, but this characterisation of near shore areas appears not to be known because there is no contemporary consideration of their ecological and economic value. This contemporary state reflects a collective intergenerational amnesia; a shifted baseline. Loss has resulted in lower yield, from O. angasi and reef associated fishes including commercially and recreationally important species, reduced capacity for natural filtration of coastal waters, and poor expectations for the productivity of South Australian coastlines. Knowledge of the historical baseline, and a desire to see a greater abundance and distribution of O. angasi and shellfish reefs in South Australia, means this loss is now being reconciled with a range of opportunities for recovery and restoration. The costs versus benefits of each are being investigated, as well as an understanding of the factors that might affect recovery and limit the success of investment. Recovery includes communication and education of the shifted baseline. Restoration includes the development of a trial oyster reef restoration project using a range of substrates and approaches, building on ecological and historical data including quantitative estimates of historical oyster densities. Increased aquaculture for O. angasi presents a novel opportunity to recover protein production and nutrient mitigation. Support for complementary objectives is also being pursued through this work, including seagrass restoration, recreational fishing opportunities and ensuring biodiversity, within and outside marine parks.