Analyses of field moult data: prediction of intermoult period and assessment of seasonal growth in Antarctic krill, Euphausia superba Dana

A technique for moult staging Antarctic krill (Euphausia superba Dana) was used in the analysis of field samples to predict intermoult periods and hence assess growth and the effects of seasonal changes in food availability. The proportion of moulting krill was used, in conjunction with laboratory data on the duration of this phase, to predict the moulting frequency (intermoult period, IMP). The moulting frequency was then combined with appropriate daily growth increments from laboratory study to assess overall growth in the krill sampled. The effects of seasonal fluctuations in food availability on moulting frequency were examined for samples taken at five different locations and times of year. Moulting rate was not linearly related to the availability of phytoplankton, although it is likely that this factor has a marked effect. Similarly, although temperature affects IMP, the data indicate that this is not a simple relationship either. These preliminary data indicate the value of utilizing this technique in the analysis of field samples of Antarctic krill.