Natural growth rates in Antarctic krill (Euphausia superba): I. Improving methodology and predicting intermoult period

• Main Authors: Angus Atkinson, Rachael S. Shreeve, Andrew G. Hirst, Peter Rothery, Geraint A. Tarling, David W. Pond, Rebecca E. Korb, Eugene J. Murphy, Jonathon L. Watkins
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2006
• Subjects: Antarctic; Scotia Sea; Southern Ocean; Antarc*; Antarctic Krill; Euphausia superba
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.318.4391; http://222.aslo.org/lo/toc/vol_51/issue_2/0973.pdf

We used the instantaneous growth rate method to determine the effects of food, temperature, krill length, sex, and maturity stage on in situ summer growth of krill across the southwest Atlantic sector of the Southern Ocean. The main aims were to examine the separate effects of each variable and to generate a predictive model of growth based on satellite-derivable environmental data. Both growth increments in length on moulting (GIs) and daily growth rates (DGRs, mm d�1) ranged greatly among the 59 swarms, from 0.58–15 % and 0.013–0.32 mm d�1. However, all swarms maintained positive mean growth, even those in the low chlorophyll a (Chl a) zone of the central Scotia Sea. Among a suite of indices of food quantity and quality, large-scale monthly Chl a values from SeaWiFS predicted krill growth the best. Across our study area, the great contrast between bloom and nonbloom regions was a major factor driving variation in growth rates, obscuring more subtle effects of food quality. GIs and DGRs decreased with increasing krill length and decreased above a temperature optimum of 0.5�C. This probably reflects the onset of thermal stress at the northern limit of krill’s range. Thus, growth rates were fastest in the ice edge blooms of the southern Scotia Sea and not at South Georgia as previously suggested. This reflects both the smaller size of the krill and the colder water in the south being optimum for growth. Males tended to have higher GIs than females but longer intermoult periods, leading to similar DGRs between sexes. DGRs of equivalent-size