Antarctic krill (Euphausia superba) are a key component of the Antarctic food web with considerab... more Antarctic krill (Euphausia superba) are a key component of the Antarctic food web with considerable lipid reserves that are vital for their health and higher predator survival. Krill lipids are primarily derived from their diet of plankton, in particular diatoms and flagellates. Few attempts have been made to link the spatial and temporal variations in krill lipids to those in their food supply. Remotely-sensed environmental parameters provide large-scale information on the potential availability of krill food, although relating this to physiological and biochemical differences has only been performed on small scales and with limited samples. Our study utilised remotely-sensed data (chlorophyll a and sea surface temperature) coupled with krill lipid data obtained from 3 years of fishery-derived samples. We examined within and between year variation of trends in both the environment and krill biochemistry data. Chlorophyll a levels were positively related to krill lipid levels, particularly triacylglycerol. Plankton fatty acid biomarkers analysed in krill (such as n-3 polyunsaturated fatty acids) increased with decreasing sea surface temperature and increasing chlorophyll a levels. Our study demonstrates the utility of combining remote-sensing and biochemical data in examining biological and physiological relationships between Antarctic krill and the Southern Ocean environment. Antarctic krill (Euphausia superba, hereon krill) are at the centre of the wasp-waisted Southern Ocean ecosystem 1,2. Krill, due to their high lipid (oil) content (up to 40% dry weight 3,4), are vital food for predators in the region 5,6. Krill have a naturally varied diet ranging from copepods and phytoplankton such as diatoms and flagel-lates, to marine snow and even cannibalism in harsh winter conditions 4,7-9. Krill are predominantly herbivorous during the summer and are more omnivorous from autumn to spring 7. Krill diet has been assessed through several different means such as microscopy 10 , DNA extraction 11,12 and the use of signature fatty acid biomarkers 7,9. Biomarkers, such as fatty acids, have been used to examine krill health and diet previously 7,9,13-18 , as they are a reliable way of looking at the long-term diet of krill 10-12. Fatty acid biomarkers are useful as they not only broadly classify what krill are eating, but their relative and absolute amounts allow insights into how much of these prey items and types krill have consumed over a more extended period of time 7,19,20. Omega-3 (n-3) long-chain (≥C 20) polyunsaturated fatty acids (n-3 LC-PUFA) are mainly derived from phytoplankton 21,22 , and are needed for krill health, growth and reproduction. They also serve as useful biomarkers 7,23,24 in food-chain research. In particular , eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), which are known to be associated with the intake of diatoms and dinoflagellates respectively 7,13 , are needed for production of krill eggs before spawning, and for the development of the larval krill 25. Other sources for EPA and DHA may also exist. The specific source(s) of other n-3 LC-PUFA such as eicosatetraenoic acid (ETA, 20:4n-3) and docosapentaenoic acid (DPA, 22:5n-3) are not as well defined. EPA and DHA are consistently abundant in krill and make up a large
Antarctic krill (Euphausia superba) are a key component of the Antarctic food web with considerab... more Antarctic krill (Euphausia superba) are a key component of the Antarctic food web with considerable lipid reserves that are vital for their health and higher predator survival. Krill lipids are primarily derived from their diet of plankton, in particular diatoms and flagellates. Few attempts have been made to link the spatial and temporal variations in krill lipids to those in their food supply. Remotely-sensed environmental parameters provide large-scale information on the potential availability of krill food, although relating this to physiological and biochemical differences has only been performed on small scales and with limited samples. Our study utilised remotely-sensed data (chlorophyll a and sea surface temperature) coupled with krill lipid data obtained from 3 years of fishery-derived samples. We examined within and between year variation of trends in both the environment and krill biochemistry data. Chlorophyll a levels were positively related to krill lipid levels, particularly triacylglycerol. Plankton fatty acid biomarkers analysed in krill (such as n-3 polyunsaturated fatty acids) increased with decreasing sea surface temperature and increasing chlorophyll a levels. Our study demonstrates the utility of combining remote-sensing and biochemical data in examining biological and physiological relationships between Antarctic krill and the Southern Ocean environment. Antarctic krill (Euphausia superba, hereon krill) are at the centre of the wasp-waisted Southern Ocean ecosystem 1,2. Krill, due to their high lipid (oil) content (up to 40% dry weight 3,4), are vital food for predators in the region 5,6. Krill have a naturally varied diet ranging from copepods and phytoplankton such as diatoms and flagel-lates, to marine snow and even cannibalism in harsh winter conditions 4,7-9. Krill are predominantly herbivorous during the summer and are more omnivorous from autumn to spring 7. Krill diet has been assessed through several different means such as microscopy 10 , DNA extraction 11,12 and the use of signature fatty acid biomarkers 7,9. Biomarkers, such as fatty acids, have been used to examine krill health and diet previously 7,9,13-18 , as they are a reliable way of looking at the long-term diet of krill 10-12. Fatty acid biomarkers are useful as they not only broadly classify what krill are eating, but their relative and absolute amounts allow insights into how much of these prey items and types krill have consumed over a more extended period of time 7,19,20. Omega-3 (n-3) long-chain (≥C 20) polyunsaturated fatty acids (n-3 LC-PUFA) are mainly derived from phytoplankton 21,22 , and are needed for krill health, growth and reproduction. They also serve as useful biomarkers 7,23,24 in food-chain research. In particular , eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), which are known to be associated with the intake of diatoms and dinoflagellates respectively 7,13 , are needed for production of krill eggs before spawning, and for the development of the larval krill 25. Other sources for EPA and DHA may also exist. The specific source(s) of other n-3 LC-PUFA such as eicosatetraenoic acid (ETA, 20:4n-3) and docosapentaenoic acid (DPA, 22:5n-3) are not as well defined. EPA and DHA are consistently abundant in krill and make up a large
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