Changes of physiological status in Antarctic krill Euphausia superba in response to light regime
simulation
M. Teschke S. Kawaguchi
B. Meyer
Alfred Wegener Institute for Polar and Marine Research – AWI Australian Antarctic Division – AAD
Introduction
• Which physiological mechanisms allow krill to survive during winter when the ocean is covered by ice and food (phytoplankton) is scarce?
• Overwintering success is a decisive factor that influences krill condition, recruitment and population size.
• The reduction in metabolic rates (30 – 50%) is discussed as a major physiological response to the Antarctic winter.
The mechanisms that causes the reductions are still not clearly known !
Research Objectives
• Are reduced metabolic rates resulting from lower food availibility (starvation) or from major physiological changes (adaptation) ?
• Internal physiological processes in krill may be influenced or induced by the seasonal light regime in the Antarctic ?
Investigate the effect of simulated Antarctic light regimes on physiological parameters of krill.
• Which environmental parameters may affect the metabolism ?
Methods
• Krill maintenance
Aurora Australis on-board tank 200 L
0°C dim light
AAD holding tank 1670 L
0.5°C nLD
experimental tank I 100 L 0.5°C LL; 200 lx
experimental tank II 100 L 0.5°C LD 12:12; 50 lx
experimental tank III 100 L 0.5°C DD 30 May 2005
17 Feb 2005
22 Aug 2005 7 Feb 2005
experiment collection
maintenance Aurora Australis on-board tank
200 L 0°C dim light
AAD holding tank 1670 L
0.5°C nLD
experimental tank I 100 L 0.5°C LL; 200 lx
experimental tank II 100 L 0.5°C LD 12:12; 50 lx
experimental tank III 100 L 0.5°C DD 30 May 2005
17 Feb 2005
22 Aug 2005 7 Feb 2005
experiment collection
maintenance Aurora Australis on-board tank
200 L 0°C dim light
AAD holding tank 1670 L
0.5°C nLD
experimental tank I 100 L 0.5°C LL; 200 lx
experimental tank II 100 L 0.5°C LD 12:12; 50 lx
experimental tank III 100 L 0.5°C DD 30 May 2005
17 Feb 2005
22 Aug 2005 7 Feb 2005
experiment collection
maintenance Aurora Australis on-board tank
200 L 0°C dim light
AAD holding tank 1670 L
0.5°C nLD
experimental tank I 100 L 0.5°C LL; 200 lx
experimental tank II 100 L 0.5°C LD 12:12; 50 lx
experimental tank III 100 L 0.5°C DD 30 May 2005
17 Feb 2005
22 Aug 2005 7 Feb 2005
experiment collection
maintenance
Methods
• Experimental design
Time (hours)
0 2 4 6 8 10 12 14 16 18 20 22 24
Light intensity (lx)
0 25 50 75 100 125 150 175 200 225
Time (hours)
0 2 4 6 8 10 12 14 16 18 20 22 24 0
25 50 75 100 125 150 175 200 225
Time (hours)
0 2 4 6 8 10 12 14 16 18 20 22 24 0
25 50 75 100 125 150 175 200 225
LL LD 12:12 DD
All three experimental stocks were fed daily the same food concentration !
Simulated Antarctic light regimes for 12 weeks
Methods
• Weekly measurements
• Feeding activity
Clearance rate Daily C ration
Size of digestive gland
• Metabolic activity
Respiration rate
Malate dehydrogenase (MDH) activity
Results
• Feeding activity → Clearance rate
LL LD 12:12 DD
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 0
1 2 3 4 5 6 7 8 9 10 11 12
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 0
1 2 3 4 5 6 7 8 9 10 11 Y = 0 .2 7 8 6 x + 1 .4 4 7 12
r2 = 0 .7 4 1 3
Y = 0 .0 3 7 4 x - 1 .8 7 9 r2 = 0 .0 7 9 2
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 Clearance rate ml (mg body C)-1 h-1
0 1 2 3 4 5 6 7 8 9 10 11
12 Y = 0 .6 2 7 8 x + 1 .4 4 7 r2 = 0 .7 8 1 0
• Feeding activity → Daily C ration
Results
LL LD 12:12 DD
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 Daily ration (% body C d-1)
0 5 10 15 20 25 30 35 40 45 50
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 0
5 10 15 20 25 30 35 40 45 50
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 0
5 10 15 20 25 30 35 40 45 Y = 2 . 5 1 5 x + 1 . 2 5 9 50
r2 = 0 . 7 8 0 7
Y = 0 . 9 1 5 x + 4 . 1 6 2 r2 = 0 . 8 4 9 9
Y = 0 . 1 5 8 3 x + 3 . 8 9 4 r2 = 0 . 0 7 9 2
Results
• Feeding activity → Digestive gland size
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Digestive gland length (% body length)
6 8 10 12 14 16 18
20 LL
LD 12:12 DD
b c a
a b
a
a a a a
Results
• Metabolic activity → Respiration rate
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Respiration rate (µl O2 ind-1 h-1 )
0 5 10 15 20 25 30 35 40 45 50 55 60 65
70 LL
LD 12:12 DD
b b
b a
b
c
c
Results
• Metabolic activity → MDH activity
Time (weeks)
0 1 2 3 4 5 6 7 8 9 10 11 12 13
MDH activity (U g fw-1 )
100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440
460 LL
LD 12:12
DD c
b
c
Summary
• LL and LD 12:12 → showed an increase in all measured parameters over the experimental period.
• LD 12:12 → showed a more consistent increase and remained below those of krill held under LL.
• DD → did not respond to the high food availability.
• Changes of feeding and metabolic activity are not primarily the result of food supply !
Feeding and metabolic activity of krill were affected by the different simulated Antarctic light regimes !
Conclusions
• Seasonal changes in the physiological status of adult krill appear to be more the result of seasonal adaptations in the animal physiology and behaviour irrespective of ambient food levels.
This may indicate an inherent adaptational overwinter strategy triggered by the Antarctic light regime !
• The study underlines the important effect of the Antarctic light cycle on physiological parameters of krill such as feeding and metabolic rates.
Future work
• Characterization on the effects of light.
• Investigate the nature of this hormone and its mode of action
~1 pg mgfw-1 (eyestalks) and ~0.2 pg µl-1 (hemolymph) immunureactive melatonin (unpublished data).
• What are the transducers for seasonal responses in relation to the Antarctic light regime (e.g. Melatonin, Serotonin) ?
Acknowledgements
Australian Antarctic Division (AAD) R. King
T. Yoshida
This work was funded by the German Academic Exchange Service (DAAD)
