A biochemically based modeling study of the growth and development of Antarctic krill (Euphausia superba)
Zusammenfassung der Projektergebnisse
A biochemical model of Antarctic krill (Euphausia superba) was developed to investigate the physiological mechanisms which enable krill to survive winter when food is scarce. The novelty of this modelling approach was that data sets on the biochemical composition of krill and its food sources were combined into a model that takes food quality into account rather than just food availability during different seasons. Krill is defined in terms of protein, neutral lipid, polar lipid, carbohydrate, chitin, and ash and the model includes parameterizations of filtration, ingestion, and metabolic processes, which determine krill growth rate. Changes in the initial ratios of protein, neutral lipid, polar lipid, carbohydrate, and chitin occur in response to the biochemical composition of available food as krill grows. Another unique aspect of this project was that through a close collaboration with krill physiologists important knowledge gaps concerning krill metabolism were identified and field experiments were planned and realized together. This data was then incorporated in the model and stresses the great benefit of collaborations between observationalists and modelers. Simulations with the model showed that a diet of phytoplankton food alone may be sufficient for krill to grow to observed sizes but may not be sufficient to provide the summer lipid resources that are observed in the field and that are necessary for krill to reproduce and survive winter. The inclusion of sea ice algae as an additional food is beneficial for krill at the end of winter but does not significantly change summer krill lipid content. However, the amount of lipids accumulated within krill increases significantly when krill feeds on lipid-rich heterotrophic food, which points to the importance of carnivory, even in times when phytoplankton food is available. Further simulations showed survival times for 72-212 days for 10 to 60 mm krill during starvation, indicating longer survival times for larger individuals. This trend matches data from laboratory experiments that showed that adult krill can survive between 150-210 days and shows that juvenile and adult krill are well prepared to survive winters without food. From the simulations it can be concluded that shrinking in size and using up body reserves plays a major role in surviving times of low food supply. This strategy is the greatest source of energy for krill in the model. Surprisingly, the reduction of krill metabolism by 50% in winter, which has been thought to be an important survival strategy of krill, is of secondary importance in this model. Model results also showed that extensive lipid utilization alone does not have a high impact on krill survival. Turning off this strategy reduces survival by amounts similar to those caused by reduction of metabolism and therefore is not effective in helping krill through winter. However, this is also a function of the amount of lipids stored in krill. Model results showed that phytoplankton alone is not sufficient to induce the observed lipid content of krill of all stages over most of the year. It became apparent that krill needs to feed on substantial amounts of lipid rich food, such as copepods, to accumulate their observed lipid content. This means that copepod food and with it the survival strategy omnivory is important lo krill. When krill is able to feed on lipid rich food before starving, the strategy of lipid utilization becomes equally important as the reduction of metabolic rates. In a next step the biochemical model was applied to the Lazarev Sea, where the regional environmental conditions were simulated using output from a finite element model of Southern Ocean hydrography and biochemistry (FESOM) and were used in connection with the biochemical krill model to test the implications for krill growth and survival and with it for population dynamics in the Lazarev Sea. First results indicated a connection of the local krill population with krill in the eastem Weddell Sea as well as the potential for recruitment of krill to areas further down stream of the Lazarev Sea. In addition, it was shown that although phytoplankton concentrations are high in austral summer in the Lazarev Sea, they are not enough to produce observed growth rates of krill in the area which points to the importance of two survival strategies for krill in this area: the need for feeding during winter, e.g. on algae and copepods under sea ice, or the necessity to feed on additional lipid rich food before winter to accumulate sufficient lipid reserves before the onset of winter. The amount of Zooplankton available to krill in the simulations though high in summer time proved to be insufficient to build up such lipid reserves. Resulls from this work are important for the development of future krill fisheries management models.
Projektbezogene Publikationen (Auswahl)
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(2005) A biochemically based modeling study of the growth and development of Antarctic krill (Euphausia superba). 22. Internationale Polartagung, Jena, Germany, 19-24 September 2005
Fach B.A., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2006) A biochemical model of the growth and development of Antarctic krill (Euphausia superba). AGU Ocean Sciences Meeting, Honolulu, Hawaii, USA, 20-24 February 2006
Fach BA., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2006) A biochemical model of the growth and development of Antarctic krill (Euphausia superba). EOS, Transactions, AGU, 87(36), Ocean. Sci. Meet. Suppl. Abstract OS34H-06
Fach B.A., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2006) A biochemically based modeling study of Antarctic krill (Euphausia superba) growth and development. SCAR Open Science Conference, Hobart, Australia, 12-14 July 2006
Fach B.A., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2006) A biochemically based modeling study of the growth and development of Antarctic krill (Euphausia superba). DFG Kolloquium, Bremerhaven, Germany, 20-21 March 2006
Fach B.A.
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(2007) Antarctic krill growth models. International Lenfest "Workshop to identify and resolve key uncertainties in Management models for krill fisheries", Santa Cruz, CA, USA, 21-24 May 2007
Fach B.A.
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(2007) Distribution of Chlorophyll-a in the Lazarev Sea. In: The expedition ANTARKTIS-XXIII/2 of the research vessel "Polarstern" in 2005/2006, Strass V. (Ed.). Berichte zur Polar- und Meeresforschung = Reports of Polar and Marine Research, 568, 139pp
Fach H.A., Schmidt G., Auerswald L., Hayden A., Herrmann R., Hohn S., Krägefsky S., Meyer B.
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(2007) Modeling Antarctic krill (Euphausia superba) development in the Lazarev Sea. EGU General Assembly, Vienna, Austria, 16- 20 April 2007
Fach B.A., Timmermann R., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2007) Modeling Antarctic krill (Euphausia superba) development in the Lazarev Sea. Geophysical Research Abstracts, Vol. 9, p. 219
Fach B.A., Timmermann R., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2007) Modeling Antarctic krill growth and survival under different environmental conditions. International workshop "The effect of climate and human related changes on marine ecosystems ", Izmir, Turkey, 18-20 October 2007
Fach B.A.
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(2007) Seasonal dynamics of physiological conditions of krill with emphasis on the larval stages - LAKRIS subproject 4. In: The expedition ANTARKTIS-XXIII/2 of the research vessel "Polarstern" in 2005/2006, Strass V. (Ed.). Berichte zur Polar- und Meeresforschung = Reports of Polar and Marine Research, 568, 139pp
Meyer B., Auerswald L., Fach B.A., Fuentes V., Hayden A., Pape C , Spahic S.
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(2008) Antarctic krill models. ICED Southern Ocean Food Web Modeling Workshop, Norfolk, VA, USA, 16-18 April 2008
Fach B.A.
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(2008) Modeling the effect of environmental influences on different species: examples of Antarctic krill and Black Sea anchovy. International workshop "Modeling climate changes in marine systems", Hamburg, Germany, 10 April 2008
Fach B.A.
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(2008) Modeling the influence of environmental conditions on Antarctic krill (Euphausia superba) population dynamics. AGU Ocean Sciences Meeting, Orlando, Florida, USA, 2-7 March 2008
Fach B.A., Timmermann R., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2008) Modeling the influence of environmental conditions on Antarctic krill (Euphausia superba) population dynamics. EOS, Transactions, AGU, Ocean. Sci. Meet. Suppl., p. 107
Fach B.A., Timmermann R., Meyer B., Wolf-Gladrow D., Bathmann U.
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(2008). A biochemically based model of the growth and development of Antarctic krill (Euphausia superba). Marine Ecology Progress Series, 360: 147- 161
Fach B.A., Meyer B., Wolf-Gladrow D., Rathmann U.
