Environmental Variability and Its Impact on the Reproductive Cycle of Antarctic Krill

“Recruitment potential” in Antarctic krill in the Palmer Long-Term Ecological Research (LTER) study region west of the Antarctic Peninsula varied significantly over the 7-yr time series between January 1993 and January 1999. Timing of ovarian maturation, the percent of the population reproducing, and individual reproductive output (batch volume, embryo diameter) were measured. Indices have been developed to quantify the timing and intensity of reproduction in Antarctic krill. One finding important to estimates of population fecundity for this long-lived species is that the percent of the population reproducing can vary widely, from 10 to 98%. Each season was characterized as having delayed, average or advanced ovarian development. In this study we relate these indices to direct and indirect indicators of spring or annual food availability. The timing of the spring sea ice retreat and the extent of sea ice in the spring (September through November) appear to significantly affect the intensity and timing of reproduction in the population. Intensity of reproduction was highest under “average” conditions, and oöcyte development fastest with conditions of a late retreat and high spring sea ice extent.