Robertson-Andersson, D. V.; Bolton, J. B.; Anderson, R. J. & Probyn, T. A.

CULTIVATION OF ULVA IN AQUACULTURE EFFLUENT

AFASA project meeting 2003

Why cultivate seaweeds on abalone farms?

• Mixed diet gives better growth rates

• MSY of kelp bed reached in 2002

•Potential over-harvesting

•Decrease in epiphyte densities

• Limited suitable coastal areas

• ‘HAB’s’

• Recirculation

• Integration will improve water quality

AIMS

1) Feasibility of growing commercially useful amounts of Gracilaria and Ulva

2) Influence of different growth media (seawater, abalone and turbot effluent water and fertilized seawater) on growth rates and yields.

3) Seasonal changes in tissue N and P content

4) Relationships between stocking density and yield

5) Uptake rates of various nutrients at differing stocking densities

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

• 12 Ulva tanks (5 X 1 X 0.63 m) & 12 Gracilaria tanks

• Run as a commercial operation

• + 4 volume exchanges per day (later changed to 12)

• 8 filtered seawater tanks

• 8 pulse fertilized sea water tanks

• 8 abalone effluent tanks

1 2 3 4 1 2 3 4 1 2 3 4

Sea water Fertilized sea water Abalone waste water

4 V 4 V 12 V12 V 12 V 12 V

Longitudinal profile of tanks

Transverse profile of tanks

5 m

1 m

PROJECT DESIGN AT JSP

• 20 Ulva tanks (100 L) & 20 Gracilaria tanks

• Run as a experimental operation

• + 20 volume exchanges per day

• 8 filtered seawater tanks (control) 4 small and 4 medium

• 6 turbot effluent tanks

• 6 abalone effluent tanks

1 2 3 4 1 2 3 4 1 2 3 4

Sea water Turbot effluent Abalone effluent

20 20 20

Small tanks

Medium tanks

0.5 m

1 m

1 m

1 m

0

1

2

3

4

5

6

7

8

sea shaded sea fert

shaded fert abalone shaded abalone

SG

R %

day

-1

J J A S O N D J F M A M J J A S O

2

RESULTS

SGR of Ulva from June ‘01 to October ‘02 in sea, fertilized & abalone effluent water. (2) where water exchanges increased at I & J

RESULTS

RGR of Ulva from June ‘01 to October ‘02 in sea, Turbot & abalone effluent water at JSP.

0

2

4

6

8

10

12

14

28-Jul 16-Sep 5-Nov 25-Dec 13-Feb 4-Apr 24-May

13-Jul 1-Sep 21-Oct 10-Dec

SG

R (

%.d

)

Small sea Medium sea

RESULTS

SGR of Ulva from June ‘01 to October ‘02 in sea, Turbot & abalone effluent water at JSP.

0

2

4

6

8

10

12

14

28-Jul 16-Sep 5-Nov 25-Dec 13-Feb 4-Apr 24-May 13-Jul 1-Sep 21-Oct 10-Dec

SG

R (

%.d

)

Small sea Medium sea turbot

RESULTS

SGR of Ulva from June ‘01 to October ‘02 in sea, Turbot & abalone effluent water at JSP.

0

2

4

6

8

10

12

14

28-Jul 16-Sep 5-Nov 25-Dec 13-Feb 4-Apr 24-May 13-Jul 1-Sep 21-Oct 10-Dec

SG

R (

%.d

)

Small sea Medium sea turbot abalone

RESULTSMyrionema strangulans (MS)

• Brown spots

• Numbering between 5 and 10 on the holdfast section of Ulva thalli

• The spots are regular discs, 1 – 3 mm in diameter

• First record for South Africa

• Identified by Dr. Herre Stegenga

• Negative correlation between infection density and SGR

BAD INFECTION

DEAD

RESULTSMyrionema strangulans (MS)

HEALTHY

INFECTED

RESULTS

MS infestation of Ulva thalli

y = -0.4557x + 3.2565

R2 = 0.2605

0

2

4

6

8

0 1 2 3 4 5 6

B-B scale of infection

SGR

(% D

ay)

RESULTS

In Quasi-commercial system using 10 tanks:

• Summer 291 kg.wwt.m-2.d-1

• Winter 135 kg.wwt.m-2.d-1

Increase by using fertilizer and Kelpak® in effluent media at 12 volume exchanges per day

RESULT

• Summer 740 kg.wwt.m-2.d-1

• Winter 234 kg.wwt.m-2.d-1

YIELDS

RESULTS

Are important because:

• Low water exchange rate leads to:

• Carbon and nutrient limitation

• Poor condition of thalli (bleached & broken)

• Low Nitrogen content

• Low SGR

therefore low yield

Measures

• Carbon limitation in seaweeds can be shown by an increase in pH values

FLOW RATES (4, 12 & 20)

RESULTSSHADING

• Shading helps to reduce epiphytes

• Helps in decreasing MS infestations

• Helps to increase tissue N and P

• Tanks should be shaded from September to January

• Shade cloth must be 20 % not 50 %

RESULTS

Important because:

• Increases protein from wild harvest (3.7- 24 % wild to 49.8 % cultured)

• Abalone receive more protein

• Faster growth rates

How do you increase tissue nutrients?

• Faster flow rates (12 – 20 volume exchanges)

• Grown in turbot/fish or abalone effluent

• Add Fertilizer and Kelpak®

Tissue Nitrogen

RESULTSTissue Nitrogen vs. Thallus Colour

Tissue nitrogen vs. thallus colour

RESULTS

Ulva can take up 90 % of ammonium 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 but is system specific

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

RECIRCULATION

ResultsECONOMICS

RESULTSECONOMICS

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16

Years

Len

gth

(m

m)

Normal growth Accelerated growth @ 49% Accelerated growth @ 68 %

Abalone growth curves

RESULTS

31.2 % increase in weight using rotation diet vs kelp only diet over 9 months

Cost: $30 per kg X R 8 = R 240

10 (100g) abalone in 1 kg

cost per abalone = R 24

less profit and freight

= R 15 per abalone

ECONOMICS

RESULTS

Increase in SGR: 49 – 68 % per year

Normal Growth to 100g = 5 years

accelerated growth = 3.3 – 3.6 years

@ R 15 per abalone

New cost : R 12.40 – R 13.50 per abalone

Savings: 17 – 28 %

R 1.50 - R 2.60 per abalone

ECONOMICS

RESULTS

Average farm (50 tons @ 100 g per abalone)

= 500 000 100g abalone

X R 1.50 or R 2.60

EQUALS

Savings:

R 800 000 – R 1.3 million

ECONOMICS

CONCLUSIONS

• This study has shown that it is possible to grow Ulva in

abalone effluent and that it has economic benefits as well

• Yields lower than those reported in literature by 3 - 5 %

day-1, but smaller tanks were used in those studies

• It is possible to increase yields by using a pulse

fertilization, Kelpak® and effluent water as the culture

medium

• By growing a combination of Ulva and Gracilaria you can

account for seasonal growth in seaweeds and maintain a

constant yield

   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