Modeling the growth dynamics of Antarctic krill Euphausia superba

Abstract

A time-dependent, size-structured, bioenergetically based model was developed to examine the growth dynamics of Antarctic krill Euphausia superba 2 to 60 mm in size. The metabolic processes included in the model are ingestion, a baseline respiration, respiratory losses due to feeding and digestion, and an activity-based respiration factor. The total of these processes, net production, was used as the basis for determining the growth or shrinkage of individuals. Size-dependent parameterizations for the metabolic processes were constructed from field and laboratory measurements. Environmental effects were included through time series of pelagic phytoplankton concentration that were derived from data sets collected west of the Antarctic Peninsula. Slrnulated growth rates during the spring and summer for all knll size classes were consistent with published growth rates; however, initial results indcated that winter shrinkage rates were too large. Although the use of a seasonally varying resp~ration activlty factor (reduced winter respiration rates) resulted in winter shrinkage rates of adults that were consistent with observations of experimentally starved ~ndividuals, the annual change In length of specific size classes was stffl inconsistent w t h observations. Subsequent simulations examlned the effect of ingestion of sea ice algae by krill in the late winter and early spring. The annual growth cycle best matched observations, particularly those for larval and subadult krill (<35 mm), when reduced winter respiration rates and ingestion of sea ice algae were both included. These results suggest that the ability of krill to exploit a range of food sources and reduced winter metabolism rates are the mechanisms that allow krill to successfully overwinter. The need for additional observations of krill physiological processes, especially during winter, is clearly indicated.

Modeling studies of antarctic krill Euphausia superba survival during transport across the Scotia Sea

“…For 40 mm krill, this swimming speed is similar to the average speed (30 cm s -1 ) of currents at the Southern ACC Front (Orsi et al 1995). Modeling studies (Hofmann et al 1998, Hofmann & Lascara 2000 suggest that krill with initial sizes of 2 mm and 10 mm can develop to 10-12 mm and 20-30 mm, respectively, in 140 to 160 d.…”

“…Simulations of Antarctic krill growth and development are obtained using the model described in Hofmann & Lascara (2000). This size-structured, physiologically based model gives the time-dependent (t) change in the number of krill individuals (N ) in a given size class, j, as:…”

“…Those used to describe the effects of active feeding and activity levels are based on field and experimental studies and are described in Hofmann & Lascara (2000).…”

“…This is done using a physiologically based model for the growth and development of Antarctic krill (Hofmann & Lascara 2000) to assess the contribution of pelagic phytoplankton, sea ice algae and other potential food sources (e.g. heterotrophic food) to larval growth and development during transport.…”

Modelling Southern Ocean ecosystems: krill, the food-web, and the impacts of harvesting

“…For example, Murphy & Reid (2001) reproduced monthly changes in the size distribution of krill at South Georgia using a model that incorporated seasonal variability in natural mortality and growth rate. Also, Hofmann & Lascara (2000) found that it was necessary to include a seasonal change in respiration rates in order for their bioenergetic model to replicate observed patterns of growth and shrinkage.…”