Biochemically based modeling study of Antarctic krill Euphausia superba growth and development

Abstract

A biochemical model of Antarctic krill Euphausia superba was developed to investigate the physiological mechanisms which enable krill to survive winter, when food is scarce. In this modeling approach data sets on the biochemical composition of krill and its food sources are combined into a model that takes food quality into account rather than just food availability during different seasons. Krill is defined in terms of protein, neutral lipid, polar lipid, carbohydrate, chitin, and ash content, and the model tracks krill neutral lipid content separately from weight. The model includes parameterizations of filtration, ingestion, and metabolic processes which determine krill growth rate. Initial ratios of protein, neutral lipid, polar lipid, carbohydrate and ash change in chitin response to the biochemical composition of food as krill grows. Model results show that a diet of phytoplankton food alone may be sufficient for krill to grow to observed sizes but may not be sufficient to provide the summer lipid resources that are observed in the field and that are necessary for krill to reproduce and survive winter. The inclusion of sea ice algae as an additional food is beneficial for krill at the end of winter but does not significantly change summer krill lipid content. However, the amount of lipids accumulated within krill increases significantly when krill feeds on lipid-rich heterotrophic food, which points to the importance of carnivory, even in times when phytoplankton food is available. The strategy of combusting body components to produce energy (shrinking) is found to provide the greatest source of energy for krill of all sizes during times of prolonged starvation.

Simulating larval Antarctic krill growth and condition factor during fall and winter in response to environmental variability

“…5 & 6) , Daly 2004, Ross et al 2004). Modeled growth rates followed a similar seasonal trend in the start date and duration of zero or negative growth as larvae in other growth models (Hofmann & Lascara 2000, Fach et al 2008 ) of an average-sized larval krill. PB: Palmer Basin; MB: Marguerite Bay magnitude of positive and negative growth rates differed among studies, largely related to food availability and feeding efficiency.…”

“…Many studies have investigated the interaction between krill and sea ice on behavioral (Stretch et al 1988, Daly 1990, Daly & Macaulay 1991, physiological (Frazer et al 2002, Meyer et al 2002, Oakes 2008 and population scales (Siegel & Loeb 1995, Wiedenmann et al 2009), yet we continue to lack a comprehensive understanding of the mechanisms underlying the relationship between sea ice variability and larval krill dynamics. Previous modeling efforts greatly advanced our understanding of potential over-wintering strategies and requirements for Ant arctic krill (Hofmann & Lascara 2000, Fach et al 2008; however, those authors recognized the limitations of those models without empirical information regarding winter physiology and behavior, especially for larval krill.In the present study, an individual-based model (IBM) was developed for larval Antarctic krill with empirical measurements of temperature-dependent ingestion (Oakes 2008, L. B. Quetin, R. M. Ross, A. T. Lowe, S. A. Oakes, M. O. Amsler unpubl. data) and respiration rates (re-analysis of Frazer et al 2002), experimental quantification of ingestion by grazing on SIMCOs (Oakes 2008) and observations of seasonal, light-driven, diel vertical migration (DVM) behavior.…”

Developing integrated models of Southern Ocean food webs: Including ecological complexity, accounting for uncertainty and the importance of scale

“…The addition of details of the embryo-larva ascent-descent cycle, feeding and metabolism, growth and reproduction provides biological realism to the particles tracked in these Lagrangian models (e.g. Hofmann et al, 1992; Hofmann and Fach et al, 2002Fach et al, , 2008Hofmann and Husrevoglu, 2003;Fach and Klinck, 2006;Tarling et al, 2007).…”

“…Deterministic and empirical models of krill growth have been generated, which have allowed the large-scale impacts of variation in temperature and food availability to be explored (Murphy et al, 2007b). Modelling of seasonal variation in food type and quality, and krill metabolic strategy provides the ability to test the effect of different diets on krill growth (Fach et al, 2008). Statistical models of the relationship between krill recruitment strength and seasurface temperature and sea ice parameters have been developed (Murphy and Reid, 2001;Constable et al, 2003;Murphy et al, 2007a,b;Wiedenmann et al, 2009).…”

Marine plankton phenology and life history in a changing climate: current research and future directions

“…Euphausiids (differing from the copepods listed above by having much larger body size, multi-stage indirect development; potential for multi-year life span, absence of seasonal dormancy, winter “shrinkage”, and iteroparous reproduction that is either season-locked or triggered at higher frequency by episodic phytoplankton blooms) are increasingly recognized for their important roles as both predators and prey in high-latitude and upwelling ecosystems. Quantitative analysis of the life histories of several species of euphausiids is advancing ( Tanasichuk, 1998a , b ; Hofmann and Lascara, 2000 ; Cuzin-Roudy et al ., 2004 ; Fach et al ., 2008 ; Pinchuka et al ., 2008 ; Wiedenmann et al ., 2008 ; 2009 ; Feinberg et al ., 2009 ). Additional candidate groups include meroplankton ( Koeller et al ., 2009 ), pteropods, ctenophores ( Costello et al ., 2006 ), appendicularians ( Greve, 2005 ) and fish larvae (of particular interest for trophic match-mismatch analysis).…”