“Biofiltration of Shrimp Pond Effluent by Oysters in a Raceway System”

1. “Biofiltration of Shrimp Pond Effluent by Oysters in a Raceway System” Adrian B. Jones* and Nigel P. Preston C.S.I.R.O. Division of Fisheries Moreton Bay Prawn Farm Research funded by the Fisheries Research and Development Corporation Saccostrea commercialis

2. Oyster’s Filter Feeding • Oysters filter bacteria and phytoplankton and convert them to meat. • Oysters filter inorganic material and pellet smaller particles into larger pseudofacaes which can settle out of suspension. Heart - Faeces(organic) and Ammonia - Psuedofaeces (inorganic) Anus Intestine Stomach - Bacteria - Phytoplankton - Inorganic particles - Detritus Mantle Gills Hinge Labial Palps (mouth) Style Sac Adductor Muscle

3. Study Area Moreton Island Redcliffe Brisbane Moreton Bay Brisbane City North Moreton Bay Prawn Farm Stradbroke Island

4. Moreton Bay Prawn Farm

5. Need for Research • Need to recapture some of the nutrients from the high cost feed pellets which are not converted into prawn biomass. • Prawn farm effluent contains elevated concentrations of bacteria, phytoplankton, nutrients and suspended solids, which can potentially adversely affect the water quality in the receiving waters. • Sewage treatment techniques are often ineffective due to the low specific gravity of most of the effluent particles, and the high volume and salt content. They are also prohibitively expensive. • To develop a system of long term sustainable aquaculture.

6. Objectives • Quantitative determination of the changes in the chemical and biological composition of prawn farm effluent water after biofiltration by different sizes of the Sydney Rock Oyster (Saccostrea commercialis). • Phytoplankton • Bacteria • Nutrients (nitrogen & phosphorus) • Total Suspended Solids • Organic / Inorganic Ratio • Determine the most efficient system to facilitate maximum filtration by the oysters, by adjusting flow rates and recirculation.

7. Methods Effluent from shrimp pond Shrimp pond waste water pumped at constant flow rate Collect 3 replicate samples from each raceway (before and after biofiltration) for analysis of Chlorophyll a, bacterial numbers, total suspended solids, & nutrients 6 raceways stocked with oysters (3 controls and 3 treatment replicates) Biofiltered water released into the environment Biofiltered water recirculated back through the oysters for further filtering Moreton Bay

8. Raceways

9. Raceway Setup

10. Effluent Water Flow Prawn Ponds Effluent Channel Raceways Recirculating Tank Moreton Bay

11. Reduction in bacterial numbers after oyster biofiltration Continual Flow Recirculating No. of Bacteria per ml x 106 No. of Bacteria per ml x 106

12. Reduction in chlorophyll a concentration after oyster biofiltration Continual Flow Recirculating Chl a concentration (µg.l-1) Chl a concentration (µg.l-1)

13. Reduction in Total Suspended Solids after oyster biofiltration Continual Flow Recirculating 0.16 0.18 92% 0.14 0.16 118% 76% 0.14 0.12 0.12 0.1 0.1 54% 63% 0.08 Total Suspended Solids (g. l-1) Total Suspended Solids (g. l-1) 0.08 0.06 0.06 32% 0.04 0.04 19% 0.02 0.02 0 0 Control Oysters 09:00 11:00 13:00 15:00 Treatment Sampling Time Inflow Outflow Inflow Outflow

14. 0.2 2 89% 0.18 1.8 85% 0.16 1.6 0.14 1.4 66% 0.12 1.2 56% 54% Total Phosphorus (mg. l-1) 0.1 Total Nitrogen (mg. l-1) 1 0.08 0.8 0.06 0.6 0.04 0.4 0.02 0.2 0 0 Control Oysters Control Oysters Treatment Treatment Inflow Outflow Inflow Outflow Reduction in Total Nutrient Concentrations after oyster biofiltration Nitrogen Phosphorus

15. Summary of Results Water quality % Reduced after once % Reduced after threeParameter through the oysters times through oysters TSS 35% 84% Bacteria 65% 88% Chlorophyll a 61% 80% Nitrogen 39% nd Phosphorus 44% nd

16. Conclusions • Oysters can remove from suspension large quantities of phytoplankton, bacteria, nutrients and total suspended solids. • By employing recirculating within the raceway system, the effects of the oysters are enhanced significantly. • The use of oysters as natural filters of aquaculture effluent has the potential to provide: • improved water quality of pond effluent and hence reduced environmental impact. • reduced pond water exchange through recirculation of biotreated water back into the ponds. • recapturing of nutrients. • increased profits. • increased productivity. • more productive method of growing and fattening oysters.

17. Continued Research • Filtration efficiency of oysters at different densities. • Test effects of flow rate, versus recirculation of water through the oysters. • Test the efficiency of different sized oysters and determine their growth rate versus those in control oceanic waters. • Test the ability of macroalgae (Gracilaria edulis) to remove dissolved nitrogen and phosphorus. • Undertake commercial scale system at Rocky Point Prawn Farm.

18. Study Area Moreton Island Redcliffe Brisbane Moreton Bay Brisbane City North Moreton Bay Prawn Farm Stradbroke Island

19. Pond Design Layout Oyster Rafts Settling Area Macroalgal Area Outflow Inflow Baffle to slow water Baffles to force water up into oyster trays

20. Integrated Aquaculture Farm Harvested Harvested Harvested - Bacteria - Phytoplankton - Inorganic particles - Detritus - Faeces(organic) and Ammonia - Psuedofaeces (inorganic) Oyster Macroalgae - Faeces(organic) and Ammonia - Psuedofaeces (inorganic) Nutrient rich food source - high in amino acids Shrimp Harvested Harvested Clam Abalone