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

PILOT, COMMERCIAL SCALE, CULTIVATION OF ULVA AND GRACILARIA ON AN

ABALONE FARM AT DANGER POINT (CAPE SOUTH COAST)

INTRODUCTION

• Supplying abalone with a mixed diet gives better growth rates than do single-species diets

• Potential over- harvesting of natural kelp beds

• Limited suitable coastal areas

• S.A. abalone farms are threatened by ‘HAB’s’

• Incorporation of seaweeds into farm effluent system will improve water quality by reducing nutrient levels

AIMS

1) To assess the feasibility of growing commercially useful amounts of Gracilaria and Ulva

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

PROJECT SITE

Abalone mariculture farm

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

PROJECT DESIGN

• 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 fresh 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

PROJECT DESIGN

• Tanks supplied with air from a blower for the tumble culture

• Ulva initially collected from Simons Town

• Hoped to be a vegetative free-floating form of U. lactuca

• Gracilaria collected from Saldanha Bay

• Stocking density 2 kg m-2 of surface area

METHODSHarvesting

• Monthly

• Tanks are scrubbed to remove fouling algae

• Tanks harvested, weighed, then restocked

• Samples were taken to record dry to wet weight and for biochemical analysis

Growth Rate Experiments

• Relative Growth rate (RGR = % d-1)

RGR = [ln(Wt / W0)] / (tt – t0)

• The yield (Y = kg wwt m-2 d-1)

Y = [(Wt – W0) / t] / SA

0.0

1.0

2.0

3.0

4.0

5.0

Sea

RG

R %

day

-1

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

1 3

2

RESULTS

RGR of Ulva from June ‘01 to Aug ‘02 in sea. (1) Indicates where shading started, (2) where water exchanges increased and (3)

indicates where shading stopped.

0

2

4

6

8

Sea Fertilizer Abalone

RG

R %

day

-1

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

13

2

RESULTS

RGR of Ulva from June ‘01 to Aug ‘02 in sea, fertilized & abalone effluent water. (1) Indicates where shading started, (2) where water

exchanges increased and (3) indicates where shading stopped.

0

1

2

3

4

5

6

Shaded Sea Shaded Fert Shaded Abalone Fertilizer

RG

R %

day

-1

J F M A M J

2

RESULTS

RGR of Ulva from June ‘01 to Jun ‘02 in sea, shaded sea, fertilized & abalone effluent water. (2) Indicates where water exchanges

increased.

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

BAD INFECTION

DEAD

RESULTSMyrionema strangulans (MS)

HEALTHY

INFECTED

0

1

2

3

4

5

6

7

SEA SHADED SEA FERT

SHADED FERT ABALONE SHADED ABALONE

J J A S O N D J F M A

2

RG

R %

Day

-1 1

RESULTS

RGR of Gracilaria from June ‘01 to April ’02 in Sea, fertilized & abalone effluent water. (1) Indicates where shading started

(2) indicates where volume exchanges changed from 4 to 12.

RESULTS

Reasons for low RGR in summer:

• Low water exchange rate

• Poor condition of thalli (bleached & broken)

• Algae are either nutrient or carbon limited

• An indication of Carbon limitation can be shown by an increase in pH values

6.5

7

7.5

8

8.5

9

9.5

10

10.5

UNSHADED SEA SHADED SEA UNSHADED FERT

SHADED FERT SHADED ABALONE UNSHADED ABALONE

8 10 12 14 16 / 9 11 13 15 17 19 21 23 /1 3 5 7 8 12 16 20

Cool Day Pulse fertilization

Hot Day

RESULTS

pH values for Ulva at 4 V exchanges day-1

CONCLUSIONS

• Low water exchange rates are causing low RGR due to carbon limitation

• Shown by increase in pH in slow flow tanks

• Bleaching of thalli

• Low RGR in summer

• Further damage is caused by high temperatures in tanks and by high UV exposure

• Which in the case of Ulva leads to MS infestations

CONCLUSIONS

• RGR is light and not temperature dependant

• Using a pulse fertilization and effluent water is the best culture medium

• Tanks should be shaded from September to January

• Shade cloth must be 20 % not 50 %

• Yields lower than those reported in literature by 3 - 5 % day-1, but smaller tanks were used in those studies

• 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

N R F

Swedish and South African Collaborative Programme

PO4 values for abalone incoming and out going water in shaded and unshaded tanks of Ulva. Area between red lines

is range for seawater.

RESULTS

0

2

4

6

8

10

8 16 24 32 40 48 56 64

ABA IN ABA NO S ABA SHADE

µ M

PO

4 /

L

30

395509

641

8021 11

0

100

200

300

400

500

600

700

8 16 24 32 40 48 56 64

FERT IN FERT NO S FERT SHADE

PO4 values for Fertilized incoming and out going water in shaded and unshaded tanks of Ulva. Area between red lines

is range for seawater.

RESULTSµ

M P

O4 /

L