| Most of the Antarctic areas are covered by sea ice year round,and the climate is extremely cold.Due to its unique geographical location and climatic characteristics,a natural environment of extreme cold,high salty environment,low light level,and strong radiation is formed here.However,there are still abundant living resources,including penguins,seals,fish and phytoplankton,etc.Antarctic krill（Euphausia superba）is one of the most aboundant species,and is mainly distributed in the Atlantic Sector,Antarctic,especially around the South Shetland Islands,the Livingston Island,the South Orkney Islands and the South Georgia Island,the biomass in the Bransfield Strait and the Weddell Sea area are also relatively high.Antarctic krill plays an important role in the entire Southern Ocean food web,acts as a key linkage connecting primary producers and higher-level predators,and as a very important fishery resource as well.Currently,a number of countries are already fishing commercially for Antarctic krill.Scientists in many countries have conducted in-depth studies on many aspects of Antarctic krill,including feeding habits,but the seasonal and interannual aspects on its feeding habit are still kept unknown.In this study,a total of 319 samples collected from February to September 2018 and April to May from 2015 to 2019 were used to conduct basic biological research,seasonal research and interannual research based on fatty acid analysis,which explores the differences in the feeding habits of Antarctic krill at different time scales,and provides scientific ideas for the further research of Antarctic krill in feeding ecology,and provides basic data for the relevant research of the Southern Ocean ecosystem food web.All samples of this experiment were collected by sea observers,placed in a test tube and stored in an deep-freezer temperature environment and shipped back to the laboratory,where the basic data such as the standard length,body weight,and sex of Antarctic krill were measured.Based on the basic data to analyze the basic biological characteristics of Antarctic krill such as standard length,weight distribution,standard length-weight relationship,sex ratio,etc.,to provide basic data support for the subsequent feeding research and obtain the basis information.The following are the main conclusions of the basic biology,（1）The total standard length range of Antarctic krill in this study is 30.03～56.81mm,and the average standard length is 43.49±4.62mm.The standard length distribution of male and female krill is similar to the overall distribution trend,which are high in the middle and low in both sides.The total body weight range of Antarctic krill is 0.16～1.43g,and the average body weight is 0.66±0.24g.The body weight distribution of male krill is consistent with the overall distribution trend,while the female krill is more concentrated in the lighter parts.（2）The total relationship between standard length and body weight was W=5.2×10-6L3.1051（R2=0.8390）,and the relationship between standard length and body weight of male krill was W=1.1×10-5L2.9042（R2=0.7577）,the relationship between standard length and body weight of female krill was W=2.8×10-6L3.2605（R2=0.9056）,and the standard length and body weight relationship between male and female krill was significantly different.（3）The sex ratio of male krill to female krill is 1.66:1.There was no significant difference in sex ratio between standard length groups.（4）In the four seasons,30 kinds of fatty acids were detected in spring,autumn and winter,and 26 kinds of fatty acids were detected in summer.Among them,saturated fatty acids C14:0 and C16:0,monounsaturated fatty acids C16:1n7 and C18:1n9c and polyunsaturated fatty acids C22:2n6,C20:5n3（EPA）and C22:6n3（DHA）are the main fatty acids,and all fatty acids show a certain periodical change in seasons,C16:1n7 and C22:2n6 have the highest content in autumn,the lowest content occurs in summer,and the other five fatty acids are consistent with the seasonal change of total fatty acid content,all of which have the highest content in autumn and the lowest in spring.It shows that krill feeds in the spring,summer and autumn,and the lipid accumulation reaches the highest in the autumn,the food intake is reduced due to the reduction of the amount of biological resources in winter and early spring.In addition,the seasonal changes of C20:1+C22:1,C18:1n9 andΣC15+ΣC17 reveal that krill are mainly herbivorous in summer,and have more carnivorous and bacterial feeding during autumn and winter for omnivorous.（5）In the five years,28 fatty acids were detected in 2015,29 in 2016,30 in 2017and 2018,and only 26 in 2019.Among them,C14:0,C16:0,C16:1n7,C18:1n9c,C20:5n3（EPA）and C22:6n3（DHA）are the six main fatty acids in each year.C20:5n3（EPA）and C22:6n3（DHA）accounted for a relatively high proportion of fatty acids in 2015 and2016,both of which fell to their lowest levels in 2018,while the percentage content of C20:1+C22:1 andΣ15+Σ17 peaked all appeared in 2018,indicating that krill were more phytoplankton in other years,but more omnivorous in 2018.There was a strong positive correlation between standard length and C16:1n7,C20:5n3.The negative correlation between standard length and C20:1+C22:1,Σ15+Σ17,which further illustrated that krill in 2018 changed from omnivorous to more phytophagous as the individual grew.This study conducted a preliminary study on seasonal and interannual feeding habits of Antarctic krill.Seasonal studies can reflect the differences in krill’s feeding due to seasonal changes,help to better understand the life history of krill and provide data for exploring its wintering mechanism.Comparing the fatty acid composition patterns of krill food sources during the interannual period helps to explore the krill feeding trends on a large time scale. |
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