Long-Term Effect of Photoperiod, Temperature and Feeding Regimes on the Respiration Rates of Antarctic Krill (<i>Euphausia superba</i>)

Abstract

Antarctic krill is thought to undergo an annual cycle of biological processes to cope with seasonal changes in their environment. The question of whether, and to what degree, seasonal environmental parameters such as photoperiod, food availability and temperature govern metabolism in krill is not clear. In this long-term laboratory study, respiration rates were determined in krill incubated under simulated natural light cycle or total darkness, subjected to fed or starved conditions and on krill kept at different temperatures (−1˚C, 1˚C and 3˚C). There was a strong and significant increasing trend of respiration rates with month in all experimental treatments. In August (late winter), the mean respiration rates ranged between 0.22 -0.35 μL O 2 mg·DW ). The covariate total length of krill was found to be non-significant and there was generally no significant interaction of experimental treatment with month and only for photoperiod comparison was the treatment main effect significant. The dark treatment gave higher respiration rates, and this needs careful interpretation. Results here suggest that, although light, food availability and temperature significantly affect metabolic rates, overall general seasonal pattern of winter low-summer high in respiration observed through the current experiment seemed to have followed an endogenous seasonal rhythm which had already been adjusted to the annual cycle prior to commencement of the experiment.

Physiological response of adult Antarctic krill, Euphausia superba, to long-term starvation

“…The presence of food alone is not sufficient to trigger feeding activity (Atkinson et al 2002;Teschke et al 2007). Recent research indicated that endogenous (inherent) mechanisms exist to synchronise the seasonal and circadian rhythmicity of metabolic and physiological output (Teschke et al 2007(Teschke et al , 2008(Teschke et al , 2011Mazzotta et al 2010), triggered by light (Seear et al 2009;Teschke et al 2011;Brown et al 2013). On the other hand, it was clearly shown in short-term starvation experiments that food availability does play a role: even after only 18 days without food, krill switched to a mode that reduced energy consumption and initiated consumption of body lipids (Atkinson et al 2002;Auerswald et al 2009).…”

Euphausiid respiration model revamped: Latitudinal and seasonal shaping effects on krill respiration rates

“…from regions across the whole Antarctic Ocean. This pattern shows evidence for a general metabolic strategy in E. superba, which has been investigated from the molecular (Seear et al, 2009;Teschke et al, 2011) to the organism level Teschke et al, 2007;Gaten et al, 2008;Pape et al, 2008;Brown et al, 2013). Although, the signaling cascade that links the photoperiod cue to the target response still remains unknown, the photoperiodic cycle clearly seems to act as a major Zeitgeber for the seasonal cycle of RR, suggesting that krill has evolved an endogenous time keeping system that perceives seasonal variations in photoperiod (Meyer, 2011).…”

“…Thus, the seasonal cycle of RR in krill could be linked to an endogenous timing system, synchronized with the seasonal course of photoperiod in the environment. In a long-term experimental study lasting several years, Brown et al (2013) maintained E. superba first under simulated natural photoperiod, before they exposed part of the group to complete darkness and variable food availability and temperature over several months. These experiments showed that E. superba maintained similar RR patterns under constant darkness as under a simulated natural light regime.…”

Internal physiology of live krill revealed using new aquaria techniques and mixed optical microscopy and optical coherence tomography (OCT) imaging techniques

“…Current experimental procedures typically necessitate krill being sacrificed to determine any effect of environmental change on krill anatomy (e.g. Brown et al, 2013).…”

“…Observing any environmentally induced physiological effect typically requires the sacrifice of individual animals precluding repeated measures type analysis and requiring large control and treatment group sizes (e.g. Brown et al, 2013).…”