D. V. Robertson-Andersson; A. Govender; T. Probyn; C. Halling; M. Troell; J. Bolton & R. Anderson

A preliminary investigation into modelling an integrated

seaweed (Ulva lactuca) & abalone (Haliotis midae)

system

INTRODUCTION

• Previous studies in Israel here have shown that Ulva lactuca is capable of removing significant amounts of nutrients (60 – 85%) from aquaculture effluents

• Modelling these systems is built on vertical integration (i.e. not closed systems)

• Models of such systems use whole farm approaches

Benefits of a closed system

• Increase in temperature above ambient seawater equates to an increase in growth rates

• Decrease in pumping costs

• Additional safety in times of red tide and oil spills

AIMS

1) Investigate and model the physico-chemical dynamics of a farm section

2) Influence of different diet on abalone growth health and excretion rates in a closed system compared to a flow through system

3) Seasonal changes in the above

PROJECT SITES

Abalone mariculture farms

• Danger Point (I & J Mariculture Farm) + 140 km east of CT

• Jacobs Baai (Jacobs Baai Sea Products) + 120 km N of CT

PROJECT DESIGN AT I & J

• 2 Ulva tanks (5 X 1 X 0.63 m) were integrated to one abalone tank (7 X 2 X 1 m)

• Run under normal farm operating conditions

• Control are 3 flow through abalone tanks

• Seaweeds initial stocking density 2.5 kg.m-2

• Harvested every two weeks

• + 13 200 abalone (10 – 15g), total biomass 165 kg

• 20 % fresh seawater input (800 L.h-1)

• 80 % recirculated through seaweeds (3 200 L.h-1)

Longitudinal profile of tanks

Transverse profile of tanks

5 m

1 m

Longitudinal profile of tanks

Transverse profile of tanks

Seaweed tank Seaweed tank

PumpPump

Gravity feed Gravity feed

Abalone tanksAbalone tanks

Seaweed tank Seaweed tank

80 % recirculation 80 % recirculation

20 % Sea water 20 % Sea water

Over flow Over flow

PROJECT DESIGN AT JSP

• Still to build an integrated system, similar to I & J but using smaller tanks and a smaller biomass of animals due to lower flow rates

RESULTS

In this systemIn this system:

• Ulva can take up 90 % of ammonium during the day in abalone effluent at 12 volume exchanges per day

• DO values don’t go below 9 mg.l-1 at night

• Using stocking density of 3 kg.wwt.m-2 gives best uptake rates in the existing system

• Toxic ammonia never reaches levels harmful to abalone at above stocking density

Seaweed uptake

RESULTS

• Ammonium levels must remain below 0.15 uM N.L-1

• DO values between 2 and 12 mg.L-1, preferred 4 - 9

• Temperature range 9 – 22 °C, 16 – 18 °C preferred

• pH 6.5 – 8.4, 7.6 - 8.2 preferred

Abalone critical points

Balancing the equations

Using linear mass balanced equations

Multiple regression of factors

Problems putting theory and reality together

RESULTSDissolved oxygen

Dissolved oxygen in a recirculation system

5.0

7.0

9.0

11.0

13.0

incoming sea seaw eed3

15 16 20 00 04 08 12 16 20 00 04 08 12 16

RESULTSDissolved oxygen

Dissolved oxygen in a recirculation system

5.0

7.0

9.0

11.0

13.0

incoming sea Recirc seaw eed3

15 16 20 00 04 08 12 16 20 00 04 08 12 16

RESULTS

pH in a recirculation system

pH

7.0

7.5

8.0

8.5

9.0

incoming sea seaw eed3

15 16 20 00 04 08 12 16 20 00 04 08 12 16

RESULTS

pH in a recirculation system

pH

7.0

7.5

8.0

8.5

9.0

incoming sea Recirc seaw eed3

15 16 20 00 04 08 12 16 20 00 04 08 12 16

RESULTS

Temperature in a recirculation system

Temperature

7.0

12.0

17.0

22.0

27.0

incoming sea seaw eed3

15 16 20 00 04 08 12 16 20 00 04 08 12 16

RESULTS

Temperature in a recirculation system

Temperature

7.0

12.0

17.0

22.0

27.0

incoming sea Recirc seaw eed3

15 16 20 00 04 08 12 16 20 00 04 08 12 16

RESULTS

ammonium levels in recirculated tanks range between

0.003 - 0.005 uM N.L-1

ammonium levels in abalone flow through tanks

= 0.01 uM N.L-1

Ammonium levels

Major Challenges

For farm management of such a system:

• Diel relationship between oxygen and pH in the seaweed systems.

• As the seaweeds start to respire at night, abalone experience an increase in oxygen demand, due to night time feeding activity and excretion in the abalone systems, which has implications for the management of ammonia.

• Seaweed uptake decreases at night when abalone excretion reaches a maximum

• Where is the missing oxygen?

The future

• Run this study over a 18 months to obtain seasonal

changes

• Effect of diet on growth and health

• Health of abalone in an integrated closed system vs.

normal farm flow through conditions

   THE END

Thank you ACKNOWLEDGEMENTS

I would like to extend special thanks to the following people and organizations without whose help this project would be impossible:

I & J Mariculture farm particularly N. Loubser, H. Otto and L. Ansara

JSP Mariculture farm particularly K. Ruck

N R F

Swedish and South African Collaborative Programme