Age group of Euphausia crystallorophias population in the Amundsen Sea and its surrounding waters in summer based on distribution mixture analysis from total length frequency
Euphausia crystallorophias is a crucial component of the biological communities in the high-latitude coastal waters of Antarctica.However,research on the total length distribution of E.crystallorophias in the Pacific sector of the Southern Ocean remains limited.Investigating the body length of krill populations in the Amundsen Sea and adjacent areas can shed light on the species'ecological traits within this region,thereby contributing to a deeper understanding of its ecological significance in the southwestern Antarctic marine ecosystem.This study is based on samples of E.crystallorophias collected during the Chinese 38th Antarctic expedition in 2022 in the Amundsen Sea and its surrounding waters.Based on the distribution mixture analysis,the age group structure of E.crystallorophias population in these sea areas was investigated.The results indicated:1)The average total body length of E.crystallorophias in the Amundsen Sea in summer 2022 was greater than that in the surrounding waters.2)E.crystallorophias populations in the Amundsen Sea consisted of three age groups:1+,2+,3+age group,and E.crystallorophias populations in waters surrounding the Amundsen Sea consisted of two age groups:1+,2+age group.The average total body length in 1+age group in the Amundsen Sea was longer than that of the same age group in waters surrounding the Amundsen Sea,while the opposite trend was observed for the growth rate of E.crystallorophias in 2+age group.3)There were significant differences in age composition among E.crystallorophias populations in different regions.In the Amundsen Sea,the dominant age group was 3+,accounting for a proportion of 49.54％.In waters surrounding the Amundsen Sea,the dominant age group was 2+,accounting for 81.23％.In the Amundsen Sea,E.crystallorophias exhibited relatively low mortality rates after their first reproductive event,allowing them to reproduce multiple times throughout lifespan.The residual population of the reproductive group was generally larger than the recruited population.Newly matured E.crystallorophias in age 1+group might be transported westward by the Antarctic Coastal Current(AACC)into the waters surrounding the Amundsen Sea,subsequently joining age 2+reproductive population as part of the recruitment group in this region.4)The growth rate of E.crystallorophias gradually decreased with age increasing,with the growth rate in 1+age group in the Amundsen Sea higher than that in the surrounding waters,while the opposite trend was observed for the growth rate in 2+age group.The higher growth rate of E.crystallorophias in 1+age in the Amundsen Sea was likely due to the region's elevated chlorophyll a concentration during the summer,which enhanced primary productivity.As E.crystallorophias matured to age 2+,energy accumulation was primarily directed toward gonadal development.However,in the surrounding waters of the Amundsen Sea,where primary productivity was relatively lower,survival strategies tended to prioritize sustaining life over reproduction.Consequently,E.crystallorophias in 2+age group in the surrounding waters of the Amundsen Sea might allocate more energy to growth than their counterparts in the more productive waters of the Amundsen Sea.
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维普
