Attempts to restore lost shellfish reefs in Australian estuaries using recycled bivalve shells as reef cultch to attract wild oyster settlement are gaining momentum nationwide, with several pilot scale projects being undertaken in Victoria, South Australia, Western Australia, Queensland. and soon in New South Wales. Yet there has been no thorough analysis of the biosecurity risks involved or determination of best practice biosecurity principles that should be enacted to protect existing fisheries and aquaculture industries from translocation of pests and diseases into new areas. This investment focuses on the risks of dissemination of pests on the outside of oyster shells (e.g. seaweeds like Undaria, Caulerpa taxifolia, fan worms Sabella spallanzanii , sea squirts Cliona intestinalis etc. ) and endemic diseases (e.g. agents of POMS, QX disease, etc.) when used as reff clutch. The project will undertake a risk analysis that identifies the potential biosecurity hazards (pests and diseases) that could be introduced through recycling of domestically sourced native bivalve shells and will determine the relevant sanitising (risk mitigation) methods required to reduce the risk of introduction of each pest and disease of concern to an acceptable level (i.e. negligible risk).