No abstract

The Nordic krill Meganyctiphanes norvegica and Arctic krill Thysanoessa raschii both dominate the krill community within the Estuary and Gulf of St. Lawrence system where they are central forage species for its pelagic ecosystem. We developed a species‐specific physiological individual based model that implements the critical physiological processes of growth, molting, and reproduction of female adults as responses to environmental forcing. Key innovations of our approach were the decoupling between the molting schedule and growth, as well as considering two distinct sources of prey (phytoplankton and mesozooplankton). Our simulation results revealed that the details of the feeding process were critical for an accurate representation of the production dynamics of adult individuals from both species. Their specific feeding preferences on phytoplankton and mesozooplankton resulted in distinct species‐specific phenological patterns that reproduced observations. The present study highlights the importance of detailed knowledge of diet and feeding behavior of krill species to improve our understanding of population responses in a rapidly changing environment.

The aim of this study was to quantify somatic growth and reproduction of Thysanoessa raschii in response to environmental conditions in the St. Lawrence Estuary and Gulf of St. Lawrence, Canada. We sampled between 2010 and 2016 from spring to late summer and incubated individuals. Fresh molts were collected daily and measured to calculate the growth increment following the instantaneous growth rate method while eggs were counted daily. Our results showed a seasonal pattern of somatic growth and reproduction driven by temperature and chl. a concentration with a decrease in somatic growth in August when egg production was maximal, suggesting a trade-off. Functional relationship analyses revealed a narrow optimal temperature window for somatic growth with maximum temperatures observed between 1.2 and 2.0°C in the cold intermediate layer (50–150 m). Maximum egg production was observed at temperatures between 3.8 and 5.7°C in the surface layer (0–50 m). A required minimum concentration of chl. a of 9 mg.m−3 for somatic growth was observed. For egg production, the minimum observed was integrated chl. a (0–50 m) of 80 mg.m−2. We also observed the importance of optimal conditions lasting for one to 3 weeks to support biological processes in T. raschii.