The Environmental Drivers of the Physiological Condition of Young-of-Year and Mature Female Antarctic Krill: Implications for Krill Recruitment

The productivity of the Antarctic ecosystem relies on the abundance of Antarctic krill, Euphausia superba, which fluctuates on a 5-7-year cycle and is a function of recruitment and survival. Studies attempting to explain the variability in krill abundance suggest it is likely the response of a complex interplay of biological, environmental and climatic factors. We assessed the relationship between krill physiological condition (weight per unit length) and recruitment rates and sought to understand the regional environmental and large-scale climatological drivers that impact krill condition during critical life history stages. Krill were collected in the Western Antarctic Peninsula (WAP) during the Palmer Antarctica Long Term Ecological Research summer cruises from 1993-2008 and the sex, stage and condition of the krill were determined upon collection. Regional environmental data were collected aboard the same cruises and climate oscillation data were obtained from online databases. We found that diatom concentrations and sea ice cover explained most of the variance in krill condition throughout the WAP. Years of late sea ice retreat corresponded with elevated physiological condition for both young-of-years (YOY) and mature females. Mature female condition increased with respect to diatom concentration, whereas YOY condition decreased. Further, we found that the condition of YOY krill was negatively impacted during years of high krill recruitment. High krill recruitment was, in turn, positively related to the condition of mature females the preceding summer, likely in response to increased reproductive output. Our findings suggest that environmental variation affects krill recruitment by altering the physiological condition of mature krill, and that krill recruitment affects the physiological condition of YOY krill, potentially impacting their likelihood of survival to adulthood.