Shellfish reef habitats: a synopsis to underpin the repair and conservation of Australias environmental, social and economically important bays and estuaries

This report describes the historic extent and current knowledge of Australian shellfish reefs and identifies knowledge gaps and future research priorities with the aim of supporting restoration efforts.

Shellfish reefs are complex, three-dimensional living structures, which provide food, shelter and protection for a range of other invertebrate and fish species. They occur in bays, estuaries and nearshore coastal waters in both tropical and temperate regions across every state within Australia. Shellfish reefs largely occur in the intertidal and upper subtidal regions of bays, estuaries and nearshore waters with the exception of the native flat oyster (Ostrea angasi) which can form reefs at depths of up to 30 m. There are more than 2000 bivalve species likely to occur in Australian coastal waters, yet only eight oyster and mussel species are known to form clearly defined reef structures across multiple locations and at scale.

Prior to the 20th century, shellfish reefs were common features of estuarine and coastal systems and were of importance as a food source for Indigenous Australians, with considerable quantities of reef-forming species occurring in coastal food middens. Early maritime explorers such as Cook, Flinders, Eyre and Vancouver regularly referred to extensive shellfish reefs in voyage reports and journals. From early European settlement of Australia, vast quantities of oysters and mussels were harvested for food and as a source of lime for mortar used in the early construction of roads and buildings.

Throughout the 1800s and early 1900s, dredge and hand-harvest oyster fisheries were likely to have occurred in over 150 locations across eastern and southern Australia, including major coastal embayments such as Moreton Bay, Sydney Harbour, Port Phillip Bay, Gulf St Vincent, Derwent River and Princess Royal Harbour. As shellfish resources closest to Australia’s first settlements rapidly became depleted, shellfish fisheries expanded to include more distant bays and estuaries. Whilst the total State or or Australia-wide catch for any one year is unknown, records from single estuaries (e.g. 10 tonnes per week for Western Port, Victoria; 22 million oysters per year from 5 estuaries in Tasmania) indicate oyster fishing constituted some of the largest and most valuable fisheries, and indeed one of the most valuable marine industries, of the 1800s.

From historical fishery reports and media articles it is clear that early harvesting efforts were unsustainable, which led to the regulation of shellfish fisheries from as early as 1853 in Tasmania and South Australia. The oyster industry was the first (of any) fishery to be regulated by legislation in South Australia, Tasmania and Victoria, with New South Wales, Queensland and Western Australia to follow within 30 years. Yet the regulation of shellfish harvesting did little to halt the destruction of shellfish reefs and by the late 20th century, shellfish reefs had all but disappeared, with all major oyster fisheries closed by 1960.

Today, only a fraction of natural shellfish reefs still survive, notably in Hinchinbrook Channel (Queensland) Sandon River (NSW) and Georges Bay (Tasmania). Poor water quality and sedimentation as a result of catchment clearance, urbanisation and industrial pollution and diseases such as Queensland Unknown (QX) and Bonamia likely exacerbated the loss of historic shellfish reefs and may hinder their natural revival.

Examples from the United States and elsewhere have demonstrated that when restoration occurs at large scales, ecological function can be repaired and ecosystem services can be restored. The process of restoring shellfish reefs can provide both short- and long-term employment opportunities and established reefs can provide long-term economic gains for coastal communities, particularly in fishing tourism and coastal protection. The benefits provided by shellfish reefs include food provision, water filtration, fish production, coastal protection and habitat for other species. Several projects (in Queensland, New South Wales, Victoria, South Australia and Western Australia) have recently begun the process of restoring shellfish reefs for the purpose of recovering a near extinct habitat and to improve fish habitat, water quality and coastal protection. Momentum is continuing to build, with a number of other shellfish reef restoration projects expected to begin across Australia within the next 12-24 months.

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