Antarctic Krill- Biochemical tracer studies

Overwintering Strategies Larval Development

Patti Virtue, Colleen O’Brien, Toshi Yoshida, Peter Nichols

Antarctic krill -Euphausia superba

• Circumpolar distribution• Forms dense swarms

• Biomass of ~ 500 million tonnes• Wasp-waist ecosystem

krill

The Krill Fishery

• Current catch

~ 120 000 tonnes• Predicted to increase in

next few years– Increased demand for krill

products for aquaculture and human consumption (particularly krill oil)

– Improved processing techniques

Krill oils• Cardiovascular disease

• Rheumatoid arthritis

• Skin cancer

• Facial wrinkles

• PMS

• Transdermal delivery systems

"Krill is a unique oil that is rich in Omega-3 fatty acid, which repairs aging cells so well, studies show it's up to 300 times

more rejuvenating than vitamins A and E!"

Aker’s projections

• Krill oil costs US$ 200 per litre wholesale, with 100 tonnes yielding ~140,000 litres, the return is expected to be ~ US$12 million per year.

• Krill meal, depending content of proteins and astaxanthin, will at least have a value of US$ 1500 per tonne, giving a return of US$24 million a year.

• A financial analyst with the Swedish bank Enskilda in Norway has estimated the value of the Aker krill venture in terms of net profit to be US$ 3.6billion.

Krill Overwintering

• Over 50 % of krill habitat covered by ice in winter

• Very low phytoplankton concentrations in water column

50m

100m

250m

500m

750m

1000m

1500m

2000m

Eggs

Nauplius I

Metanauplius

Calyptopis III

Dev

elo

pm

ent

Life history of Life history of EuphausiaEuphausia superbasuperba

Hatch

Spawning(Summer)

Autumn-Winter

Overwintering Strategies

• Ingestion of alternative food sources– Sea-ice algae

– Copepods– Detritus

• Lipid storage• Shrinkage• Hibernation

Sample Collection

• Samples were collected off East Antarctica (110°- 130°E) as part of the Sea Ice Physics and Ecosystems eXperiment (SIPEX) in September-October 2007.

Lipid Analysis

20:5 ω3

16:0

14:0 18:0

20:1 ω9

16:1ω7

20:4 ω6

22:6 ω3

-Total lipid- condition

-Lipid class- storage/structural

-Fatty acid profiles- diet/physiology

MicroscopyMicroscopy used to determine the species composition of:– Melted ice cores – Krill stomach contents

Ice Cores

• Ice cores, although dominated by diatoms, contained very low levels of polyunsaturated fatty acids.

0%

20%

40%

60%

80%

100%

1 2 3 5 7 8 9 10 11 13 14

Ice Station #

PUFA

MUFA

SFA

Krill Fatty Acid Profiles

• Low PUFA/SFA ratio• Low ratio of 16:1ω7 to 16:0 – generally not

indicative of a diatom-based diet• Traces of copepod markers

0.00

5.00

10.00

15.00

20.00

25.00

30.00

14:0

16:1

w7c

16:0

18:4

w3

18:2

w6

18:1

w9c

18:1

w7c

18:0

20:5

w3

20:1

w9

22:6

w3

22:1

w9c

% T

ota

l Fat

ty A

cid

Larval Fatty Acid Profiles

• Higher PUFA/SFA ratio than adults, but still lower than expected for larvae with this level of lipids

• Small amounts of C17 bacterial markers

0.00

5.00

10.00

15.00

20.00

25.00

14:0

16:1w

7c

16:0

18:4w

318

:2w6

18:1w

9c18

:1w7c

20:4w

620

:5w3

22:6w

3%

To

tal

Fat

ty A

cid

Krill Condition

• Adult:– Dry mass 252 ± 58.7 mg

– Total lipid content 24.1 ± 6.7 %• Similar to summer levels

• Larvae:– Dry mass 0.9 mg

– Total lipid content 6.6 %

Starvation Experiments

• Larvae severely depleted after five days starvation

• Adults survived 207 days (until end of experiment)

0 5 12 20 26 47 207

510

1520

2530

Day

Tot

al L

ipid

(%

Dry

Mas

s)

Fatty acid dietary markers

18:4 non-diatom phytoplankton/protozoans18:5 dinoflagellate20:1 crustaceansa + i bacteriaC16 PUFA diatoms

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Summer 99 Summer 96 Polynya

% F

atty

Aci

d 18:4(n-3)

18:5(n-3)

20:1+22:1

a + i 17:0

C16 PUFA

Winter growth and condition of Ice Krill (Euphausia crystallorophias) off East Antarctica

Winter Polynya

Krill egg hatching success rate• Specific fatty acids play important roles in

embryogenesis and larval development of krill.

• Levels of the fatty acids LA and AA and the DHA/EPA ratio effect hatching success.

• The long chained PUFA are utilised at a greater rate compared to SFA and MUFA during the embryonic and larval development of krill.

Yoshida et al 2009

Krill egg hatching success rate

• Dietary condition of maternal krill affects the quality of embryos, and in turn the hatching success and larval survival.

Yoshida et al 2009

Conclusions

• Krill larvae highly dependent on ice algal community• Adult krill less so as they store lipid• Detritus and/or protozoa may be an important food

source for larval krill and copepods at this time of year.• Copepods do not appear to be a major food source for

krill in this area.• Krill caught in late September were in good condition –

enough food available to meet energy requirements.• BUT – low in essential PUFAs which are necessary for

reproduction