Feeding Of Antarctic Krill(euphausia Superba) In The South Shetland Islands Based On The Biomarker Techniques

Southern ocean has rich marine living resources, such as whales, penguins, seals and so on. However Antarctic krill occupy the most abundant. Krill likely have highly biomass potential in Antarctic ocean, and are targets of commercial fishery worldwide. Antarctic krill is mainly distributed in the Atlantic sector of Antarctic, especially in the South Shetland Islands, the South Orkney Islands and the South Georgia Island, the abundance of Antarctic krill resources are also abundant in the Bransfield Strait and the Weddell Sea. As the key species in the Antarctic marine ecosystem, Antarctic krill becomes the prey of the top predators, such as the penguins, whales, sea birds and sea seals, and on the other hand, it’s also feed phytoplankton and other plankton.Despite many countries have input a lot of efforts to research them fatherly and systemically, however, so far, studies on the feeding of Antarctic krill are still relatively scarce. Based on the samples collected from Antarctic Marine Living Resources Development and Utilization Project operated in 2012 to 2014, the basic biology of Antarctic krill around the South Shetland Islands were studied, and the feeding of Antarctic krill were studied based on the biomarker methods(fatty acid marker and stable isotopic analysis), so as to provide the scientific basis for further studying the feeding ecology of Antarctic krill, and to provide basic data for the study of the Antarctic marine ecosystem.Krill were sampled by observers and stored individually in the deep-freezer using the test tube. Antarctic krill samples were thawed in the laboratory and measured the total length, wet weight after identified sex. The biological characteristics, such as total length distribution, weight distribution and the relationship between total length- wet weight, sex ratio of the Antarctic krill were analyzed, in order to provide basic information for subsequent feeding analysis. The main conclusions of this study can be found as follows,(1) The range of total length was from 36.4 mm to 57.64 mm, the average total length was 45.24 ± 5.26 mm. The range of wet weight was from 0.2376 g to 1.3415 g, the average weight was0.6082 ± 0.28 g.(2) The relationship between total length(mm) and wet weight(g) could be described as =(4 × 10-7)3.7404, there was no significant difference for the relationship between total length and wet weight for males and females.(3) The vertical distribution of Antarctic krill aggregations were mainly ranged in 15-55 m under the sea surface, accounting to 83.24% of the total.(4) The ratio of male and female was 1: 1.31. Significant differences can be found for each total length class of Antarctic krill.(5) Antarctic krill have eight kinds of fatty acids, including C16:0, C14:0, C18:1N9c, C16:1, C20:5N3, C22:6N3, C20:2 and C18:2N6c, respectively, and the content of C16:0 was the highest, 26.49% of the total fatty acid content were C20:5N3 and C22:6N3. The Σ16/Σ18 ratios were greater than 2 in more than 63% total length classes of Antarctic krill, the ratios of C20:5N3/C22:6N3 were greater than 1 for all of total length classes, and the contents of C16:1 were higher, indicating that the diatoms occupied the dominant in the food items of Antarctic krill. The content of C22:6N3 was higher, accounting to 6.41% ~ 13.61%, while the ratios of C20: 5N3/C22: 6N3 were not less than 1, showing that the dinoflagellates were the food items of Antarctic krill. The contents of C20:1 + C22:1 occupied about 2.16% of the total fatty acid content, and higher content of C22:6N3 were found in Antarctic krill tissue, revealing Antarctic krill feed on copepods, and showed the carnivorous characteristics. The content of C20:4N6 was considered as an indicator of macroalgae, however, only some groups of Antarctic krill contained C20:4N6 and the content were extremely low in this study, indicating Antarctic krill seldomly feed macroalgae, which may be related to the feeding selectivity of Antarctic krill. Overall, in the feeding items of Antarctic krill, the content of diatoms was dominated, followed by dinoflagellates and copepods, the Antarctic krill also feed a small amount of planktonic bacteria, showed the carnivorous characteristics, and seldom feed macroalgae.(6) The range of δ13C values in the tissue of Antarctic krill were from-28.40 ‰ to-21.43 ‰, and the δ15N values were from 5.55 ‰ to 8.12 ‰, the ratios of C/N were from 3.4893 to 4.1389. The δ13C values of Antarctic krill were wider, indicating the food sources of Antarctic krill were more complex. The relationship between δ13C and δ15N values with total length of Antarctic krill showed positively correlated, but this trend was not obvious. The reason may be derived from the adult samples, the stable feeding habits of adult krill and unremarkably change in the habitat environment will result to the feeding items were similar, and the difference of stable isotopes composition converted from the feeding items were not significant. The δ13C, δ15N and C/N values of Antarctic krill samples showed an increasing trend from January- February to May-June. The habitat regions of Antarctic krill had an impact on their δ13C and δ15N values of tissues, the δ13C and δ15N values of Antarctic krill in the outside of the South Shetland Islands were significantly higher than the other two regions.In this study, the combination of the two biomarkers can be a good indicators of the material flow in the food webs. The fatty acid composition of animals can be a description of the food composition of predator more detailed and the isotopic information may reflect the material source of ecosystem. Combined the above two biomarker methods in this study is more convenient and accurate than the traditional stomach content analysis.