Biosecurity risks related to recycling of mollusc shell waste for shellfish reef restoration in Australia

Abstract

SummaryA risk analysis was undertaken to assess the biosecurity risks involved with recycling mollusc shell waste for restoration of shellfish reefs in Australia. The hazard identification stage identified 20 diseases and 14 groups of marine pests upon which detailed risk assessment was undertaken. The qualitative risk assessment process involved release, exposure and consequence assessment, to arrive at an unmitigated risk estimation as well as risk estimates for several shell treatments, including 3, 4 or 6 months desiccation in sunlight, exposure to hot water at 55°C for 10 min or 80°C for 5 min, bathing in freshwater for > 24 h or in vinegar (4% acetic acid) for 30 min. The effectiveness of these treatments as risk management options were then compared to inform development of protocols for biosecure treatment of mollusc shells. The appropriate level of protection (ALOP) was expressed in qualitative terms as ‘very low’, representing an annual probability between 1 in 20 and 1 in 100 years. The outcomes from the risk analysis indicated that heating recycled mollusc shells in water at 80°C for > 5 min would meet the ALOP for all pests and diseases of concern. This method has limited throughput, however, and thus may be useful only for pilot scale restoration projects. Desiccation of mollusc shells in sunlight for 4 months at > 20°C was also within the ALOP for all hazards examined. However, if ambient weather conditions at the recycling facility prevent the shell pile drying out or exceeding 20°C for several months of the year, extending the desiccation period to 6 months with at least one shell turnover is recommended to provide sufficient safety margin to ensure the ALOP is met. Desiccation of mollusc shells can be undertaken at vast scales at minimal cost, and thus appears suitable for shellfish restoration at environmentally meaningful scales.