Kawagushi, S.

Meyer, Bettina

Teschke, Mathias

English

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Changes of physiological status in Antarctic krill Euphausia superba in response to light regime simulationM. Teschke S. Kawaguchi B. MeyerAlfred Wegener Institute for Polar and Marine Research – AWIAustralian Antarctic Division – AADIntroduction• 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 tank200 L0°Cdim lightAAD holding tank1670 L0.5°CnLDexperimental tank I100 L0.5°CLL; 200 lxexperimental tank II100 L0.5°CLD 12:12; 50 lxexperimental tank III100 L0.5°CDD30 May 200517 Feb 200522 Aug 20057 Feb 2005experimentcollectionmaintenance    . i tenance i entMethods• Experimental design Time (hours)0 2 4 6 8 10 12 14 16 18 20 22 24Light intensity (lx)0255075100125150175200225Time (hours)0 2 4 6 8 10 12 14 16 18 20 22 240255075100125150175200225Time (hours)0 2 4 6 8 10 12 14 16 18 20 22 240255075100125150175200225LL LD 12:12 DDAll three experimental stocks were fed daily the same food concentration !Simulated Antarctic light regimes for 12 weeksMethods• Weekly measurements • Feeding activityClearance rateDaily C rationSize of digestive gland• Metabolic activityRespiration rateMalate dehydrogenase (MDH) activityResults• Feeding activity → Clearance rateLL LD 12:12 DDTime (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 130123456789101112Time (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 130123456789101112Y  =  0 .2 7 8 6 x  +  1 .4 4 7r2 =  0 .7 4 1 3Y  =  0 .0 3 7 4 x  -  1 .8 7 9r2 =  0 .0 7 9 2Time (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 13Clearance rate ml (mg body C)-1 h-10123456789101112 Y  =  0 .6 2 7 8 x  +  1 .4 4 7r2 =  0 .7 8 1 0• Feeding activity → Daily C rationResultsLL LD 12:12 DDTime (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 13Daily ration (% body C d-1)05101520253035404550Time (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 1305101520253035404550Time (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 1305101520253035404550Y  =  2 .5 1 5 x  +  1 .2 5 9r2 =  0 .7 8 0 7Y  =  0 .9 1 5 x  +  4 .1 6 2r2 =  0 .8 4 9 9Y  =  0 .1 5 8 3 x  +  3 .8 9 4r2 =  0 .0 7 9 2Results• Feeding activity → Digestive gland sizeTime (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 13Digestive gland length (% body length)68101214161820 LLLD 12:12DDb c abaaa aaaResults• Metabolic activity → Respiration rateTime (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 13Respiration rate (µl O2 ind-1 h-1)0510152025303540455055606570 LLLD 12:12DDbbbabccResults• Metabolic activity →MDH activityTime (weeks)0 1 2 3 4 5 6 7 8 9 10 11 12 13MDH activity (U g fw-1)100120140160180200220240260280300320340360380400420440460 LLLD 12:12DD cbcSummary• 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) ?AcknowledgementsAustralian Antarctic Division (AAD) R. KingT. YoshidaThis work was funded by the German Academic Exchange Service (DAAD)

Changes of physiological status of Antarctic krill Euphausia superba in response to light regime simulation

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