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 ...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 O2 mg.DW-1.hr-1 for krill in both simulated seasonal light and complete darkness, and 0.25 - 0.26 μL O2 mg.DW-1.hr-1 for both fed and starved krill. Mean maximal respiration rates were recorded in October and December for all light and feeding treatments (0.46 - 0.56 μL O2 mg.DW-1.hr-1). Mean respiration rates for krill in the temperature treatments ranged between 0.24 - 0.30 μL O2 mg.DW-1.hr-1 in September reaching mean maximal rates in November and February (0.60 - 0.71 μL O2 mg.DW-1.hr-1). 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,展开更多
In situ characterization of krill morphometry, behaviour and orientation is not yet routinely feasible, yet is critical to understanding swarm characteristics. A first step is to measure individual and aggregation beh...In situ characterization of krill morphometry, behaviour and orientation is not yet routinely feasible, yet is critical to understanding swarm characteristics. A first step is to measure individual and aggregation behaviour. We report on successful use of a robust, low-cost underwater stereo video camera system to observe live Antarctic krill (Euphausia superba) in aquaria. The application of photogrammetry techniques allows animal length, orientation and three-dimensional position to be calculated from stereo video camera observations. Initially, we tested the efficacy of the stereo system by observing synthetic targets of known length and orientation to obtain estimates of measurement error. We found that on average the stereo camera system underestimated length by 0.6 mm and vertical tilt angle by +0.34°(head up), but that photogrammetric measurements of 100 randomly selected krill lengths were not significantly different from measurements of 100 randomly caught krill measured physically. During our investigation, we analysed three krill behavioural metrics: swimming speed, tortuosity, and vertical orientation under three behavioural states (undisturbed, feeding, and escape). We found that swim speed and tortuosity significantly increased when animals were feeding or exhibiting an escape response, but vertical orientation was not significantly different across states. Our investigation demonstrates that low-cost stereo video cameras can produce precise measurements that can be used for monitoring krill behaviour and population structure.展开更多
文摘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 O2 mg.DW-1.hr-1 for krill in both simulated seasonal light and complete darkness, and 0.25 - 0.26 μL O2 mg.DW-1.hr-1 for both fed and starved krill. Mean maximal respiration rates were recorded in October and December for all light and feeding treatments (0.46 - 0.56 μL O2 mg.DW-1.hr-1). Mean respiration rates for krill in the temperature treatments ranged between 0.24 - 0.30 μL O2 mg.DW-1.hr-1 in September reaching mean maximal rates in November and February (0.60 - 0.71 μL O2 mg.DW-1.hr-1). 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,
文摘In situ characterization of krill morphometry, behaviour and orientation is not yet routinely feasible, yet is critical to understanding swarm characteristics. A first step is to measure individual and aggregation behaviour. We report on successful use of a robust, low-cost underwater stereo video camera system to observe live Antarctic krill (Euphausia superba) in aquaria. The application of photogrammetry techniques allows animal length, orientation and three-dimensional position to be calculated from stereo video camera observations. Initially, we tested the efficacy of the stereo system by observing synthetic targets of known length and orientation to obtain estimates of measurement error. We found that on average the stereo camera system underestimated length by 0.6 mm and vertical tilt angle by +0.34°(head up), but that photogrammetric measurements of 100 randomly selected krill lengths were not significantly different from measurements of 100 randomly caught krill measured physically. During our investigation, we analysed three krill behavioural metrics: swimming speed, tortuosity, and vertical orientation under three behavioural states (undisturbed, feeding, and escape). We found that swim speed and tortuosity significantly increased when animals were feeding or exhibiting an escape response, but vertical orientation was not significantly different across states. Our investigation demonstrates that low-cost stereo video cameras can produce precise measurements that can be used for monitoring krill behaviour and population structure.
