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Natural growth rates in Antarctic krill (Euphausia superba): II. Predictive models based on food, temperature, body length, sex, and maturity stage

Atkinson, Angus; Shreeve, Rachael S.; Hirst, Andrew G.; Rothery, Peter; Tarling, Geraint A.; Pond, David W.; Korb, Rebecca E.; Murphy, Eugene J.; Watkins, Jonathon L.. 2006 Natural growth rates in Antarctic krill (Euphausia superba): II. Predictive models based on food, temperature, body length, sex, and maturity stage. Limnology and Oceanography, 51 (2). 973-987.

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Abstract/Summary

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 krill tended to decrease with maturity stage, suggesting the progressive allocation of energy toward reproduction rather than somatic growth. Our maximum DGRs are higher than most literature values, equating to a 5.7% increase in mass per day. This value fits within a realistic energy budget, suggesting a maximum carbon ration of ~20% d-1. Over the whole Scotia Sea/South Georgia area, the gross turnover of krill biomass was ~1% d-1.

Item Type: Publication - Article
Programmes: BAS Programmes > Global Science in the Antarctic Context (2005-2009) > DISCOVERY 2010 - Integrating Southern Ocean Ecosystems into the Earth System
CEH Programmes pre-2009 publications > Biodiversity
CEH Sections: _ Ecological Processes & Modelling
ISSN: 0024-3590
Format Availability: Electronic, Print
Additional Keywords: Euphausiids ; Growth
NORA Subject Terms: Marine Sciences
Zoology
Date made live: 17 Aug 2007 13:33
URI: http://nora.nerc.ac.uk/id/eprint/10

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