Grazing dynamics of Euphausia spinifera in the region of the Subtropical Convergence and the Agulhas Front

2001 ◽  
Vol 58 (2) ◽  
pp. 273-281 ◽  
Author(s):  
Renzo Perissinotto ◽  
Patrick Mayzaud ◽  
Jean-Philippe Labat ◽  
Suzanne Razouls

The feeding ecophysiology of the subtropical euphausiid Euphausia spinifera was investigated in the Indian sector of the Southern Ocean during January–February 1999. Gut pigment levels varied from 1.7 to 40.6 ng chlorophyll a (Chl a) equiv.·individual–1 in adults and from 0.3 to 9.3 ng Chl a equiv.·individual–1 in juveniles. Highest levels were observed at the Subtropical Convergence (Chl a concentrations 0.4–0.6 µg·L–1) and minima in the area north of the Agulhas Front (Chl a concentrations 0.2–0.3 µg·L–1). Gut evacuation rates ranged between 0.59 and 0.96·h–1. Gut pigment destruction levels were among the highest ever recorded in euphausiids, with 94.2–98.5% of total pigments ingested converted to nonfluorescing end products. Size-selectivity experiments with natural phytoplankton showed that E. spinifera ingests mainly cells in the 0.7- to 20-µm range. The grazing dynamics of this important species are compared with those of subantarctic (Euphausia vallentini) and Antarctic krill (Euphausia superba). Individual ingestion rates, estimated from the autotrophic component of its diet (2.78–4.46 µg Chl a equiv.·individual–1·day–1), were just sufficient to account for respiratory requirements. While E. spinifera is clearly able to ingest large amounts of heterotrophic prey, it is not known to what extent these contribute to its total energy budget.

PLoS ONE ◽  
2018 ◽  
Vol 13 (8) ◽  
pp. e0202027
Author(s):  
Ludvig A. Krag ◽  
Bjørn A. Krafft ◽  
Arill Engås ◽  
Bent Herrmann

2012 ◽  
Vol 36 (2) ◽  
pp. 300
Author(s):  
Peng-xiang XU ◽  
Ying-chun LI ◽  
Guo-ping ZHU ◽  
Hui XIA ◽  
Liu-xiong XU

Polar Biology ◽  
2021 ◽  
Vol 44 (3) ◽  
pp. 483-489
Author(s):  
Bjørn A. Krafft ◽  
Ludvig A. Krag

AbstractThe use of light-emitting diodes (LEDs) is increasingly used in fishing gears and its application is known to trigger negative or positive phototaxis (i.e., swimming away or toward the light source, respectively) for some marine species. However, our understanding of how artificial light influences behavior is poorly understood for many species and most studies can be characterized as trial and error experiments. In this study, we tested whether exposure to white LED light could initiate a phototactic response in Antarctic krill (Euphausia superba). Trawl-caught krill were used in a controlled artificial light exposure experiment conducted onboard a vessel in the Southern Ocean. The experiment was conducted in chambers with dark and light zones in which krill could move freely. Results showed that krill displayed a significant positive phototaxis. Understanding this behavioral response is relevant to development of krill fishing technology to improve scientific sampling gear, improve harvest efficiency, and reduce potential unwanted bycatch.


2021 ◽  
pp. 1-13
Author(s):  
Anna Belcher ◽  
Sophie Fielding ◽  
Andrew Gray ◽  
Lauren Biermann ◽  
Gabriele Stowasser ◽  
...  

Abstract Antarctic krill are the dominant metazoan in the Southern Ocean in terms of biomass; however, their wide and patchy distribution means that estimates of their biomass are still uncertain. Most currently employed methods do not sample the upper surface layers, yet historical records indicate that large surface swarms can change the water colour. Ocean colour satellites are able to measure the surface ocean synoptically and should theoretically provide a means for detecting and measuring surface krill swarms. Before we can assess the feasibility of remote detection, more must be known about the reflectance spectra of krill. Here, we measure the reflectance spectral signature of Antarctic krill collected in situ from the Scotia Sea and compare it to that of in situ water. Using a spectroradiometer, we measure a strong absorption feature between 500 and 550 nm, which corresponds to the pigment astaxanthin, and high reflectance in the 600–700 nm range due to the krill's red colouration. We find that the spectra of seawater containing krill is significantly different from seawater only. We conclude that it is tractable to detect high-density swarms of krill remotely using platforms such as optical satellites and unmanned aerial vehicles, and further steps to carry out ground-truthing campaigns are now warranted.


1982 ◽  
Vol 33 (1) ◽  
pp. 71 ◽  
Author(s):  
T Ikeda ◽  
P Dixon

Live E. superba were transported from Antarctic waters to a tropical laboratory where observations at the temperature of -0.5�C (0 to - 1.0�C), were made of intermoult period of specimens fed a mixture of microalgae (Dunaliella tertiolecta and Phaeodactylum tricornutum) or artificial pet fish food or starved. Mean intermoult period was 26.4-27.1 days for fed specimens and 29.6 days for starved specimens, with no relation to the size of specimens. The moult accounted for a loss of 2.63-4.35% of animal dry weight, which is equivalent to 1.1-1.8% of animal nitrogen or 1.4-2.3% of animal carbon. The contribution of moults to detritus in the Antarctic Ocean was estimated as 0.11 g C m-2 per year.


Polar Biology ◽  
2021 ◽  
Author(s):  
Carmen L. David ◽  
Fokje L. Schaafsma ◽  
Jan A. van Franeker ◽  
Evgeny A. Pakhomov ◽  
Brian P. V. Hunt ◽  
...  

AbstractSurvival of larval Antarctic krill (Euphausia superba) during winter is largely dependent upon the presence of sea ice as it provides an important source of food and shelter. We hypothesized that sea ice provides additional benefits because it hosts fewer competitors and provides reduced predation risk for krill larvae than the water column. To test our hypothesis, zooplankton were sampled in the Weddell-Scotia Confluence Zone at the ice-water interface (0–2 m) and in the water column (0–500 m) during August–October 2013. Grazing by mesozooplankton, expressed as a percentage of the phytoplankton standing stock, was higher in the water column (1.97 ± 1.84%) than at the ice-water interface (0.08 ± 0.09%), due to a high abundance of pelagic copepods. Predation risk by carnivorous macrozooplankton, expressed as a percentage of the mesozooplankton standing stock, was significantly lower at the ice-water interface (0.83 ± 0.57%; main predators amphipods, siphonophores and ctenophores) than in the water column (4.72 ± 5.85%; main predators chaetognaths and medusae). These results emphasize the important role of sea ice as a suitable winter habitat for larval krill with fewer competitors and lower predation risk. These benefits should be taken into account when considering the response of Antarctic krill to projected declines in sea ice. Whether reduced sea-ice algal production may be compensated for by increased water column production remains unclear, but the shelter provided by sea ice would be significantly reduced or disappear, thus increasing the predation risk on krill larvae.


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