“Biofiltration of Prawn Farm Effluent by Oysters and Macroalgae” Adrian Jones 1, Nigel Preston 2 & William Dennison 1 1 Marine Botany, Botany Department, The University of Queensland 2 CSIRO Marine Research, Cleveland, Queensland Research funded by the Fisheries Research and Development Corporation

Need for Research Recapture nutrients from the high cost feed pellets which are not converted into prawn biomass.Recapture nutrients from the high cost feed pellets which are not converted into prawn biomass. Prawn farm effluent contains elevated concentrations of:Prawn farm effluent contains elevated concentrations of: –bacteria –phytoplankton –nutrients –suspended solids Sewage treatment techniques are often ineffective due to:Sewage treatment techniques are often ineffective due to: –low specific gravity of particles –high volume –high salt content –prohibitively expensive. To develop a system of long term sustainable aquaculture.To develop a system of long term sustainable aquaculture.

Need for Research ~ mg l WaterQualityParameter PrawnEffluentOceanicWater TSS < 2 mg l Chlorophylla ~ µg l < 1 µg l Total Nitrogen ~200 µM ~1 µM Total Phosphorus ~20 µM ~0.1 µM

Experimental Design

Unsettled

Unsettled

PrawnPonds Raceways RecirculatingTank MoretonBay

Recirculated Bacteria per ml x 10 6 Chlorophyll a (µg l -1 ) 54% 09:0011:0013:0015: Total Suspended Solids (g. l -1 ) Sampling Time 118% 63% 32% 19%

Oyster Growth

Summary Recirculating produced greater improvements in water qualityRecirculating produced greater improvements in water quality However tests on oyster growth rate demonstrated inhibition with the effluentHowever tests on oyster growth rate demonstrated inhibition with the effluent Macroalgae were also affected by the high sediment loadsMacroalgae were also affected by the high sediment loads We then tested an integrated system which employed pre- settling and also nutrient assimilation by macroalgaeWe then tested an integrated system which employed pre- settling and also nutrient assimilation by macroalgae

Filter Feeding Oysters filter bacteria and phytoplankton and convert them to meat.Oysters filter bacteria and phytoplankton and convert them to meat. Oysters filter inorganic material and pellet smaller particles into larger pseudofaeces which can settle out of suspension.Oysters filter inorganic material and pellet smaller particles into larger pseudofaeces which can settle out of suspension. AnusHeartIntestine Stomach Mantle Gills AdductorMuscle Style Sac Labial Palps (mouth) Hinge Faeces (organic) and Ammonia Pseudofaeces (inorganic) BacteriaPhytoplankton Inorganic particles Detritus

Suspended Solids Particle Size Number of Particles Control Inflow Oyster Inflow Control Outflow Oyster Outflow

Experimental Design Effluent 24 Hours Settling 0 hrs 24 hrs 48 hrs 72 hrs Shells(Control)Oysters (Rep A) Oysters (Rep B) Oysters (Rep C) No Algae (Control)Algae (Rep A) Algae (Rep B) Algae (Rep C)

Settled

Settled

Settled

Settled

Data Synthesis UnsettledRecirculatedSettled Bacteria5612nd TSS Chla Total N 78nd25 Total P 67nd14 NH 4 + ndnd90 NO 3 - ndnd28 PO 4 3- ndnd35

Summary Assimilation of nutrients by organisms can take place naturally or by employing biological filtering systems.Assimilation of nutrients by organisms can take place naturally or by employing biological filtering systems. These organisms are capable of reducing the concentrations of:These organisms are capable of reducing the concentrations of: –water column nutrient (particulate and dissolved) –phytoplankton –bacteria –suspended solids (especially the small unsettleable inorganic particles) Sedimentation is necessary to ensure the efficiency and health of the biofiltersSedimentation is necessary to ensure the efficiency and health of the biofilters