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

"Recruitment potential" in Antarctic krill in the Palmer Long-TermEcological Research (LTER) study region west of the AntarcticPeninsula varied significantly over the 7-yr time series betweenJanuary 1993 and January 1999. Timing of ovarian maturation,the percent of the population reproducing, and individual reproductiveoutput (batch volume, embryo diameter) were measured. Indiceshave been developed to quantify the timing and intensity ofreproduction in Antarctic krill. One finding important to estimatesof population fecundity for this long-lived species is thatthe percent of the population reproducing can vary widely, from10 to 98%. Each season was characterized as having delayed,average or advanced ovarian development. In this study we relatethese indices to direct and indirect indicators of spring orannual food availability. The timing of the spring sea ice retreatand the extent of sea ice in the spring (September through November)appear to significantly affect the intensity and timing of reproductionin the population. Intensity of reproduction was highest under"average" conditions, and oöcyte development fastest withconditions of a late retreat and high spring sea ice extent.