Studies of adult krill

 

Bettina Meyer1, Ulrich Freier1, So Kawaguchi2, Rob King2, Kerrie Swadling3, Patti Virtue3, Zhongnan Jia3

1. Alfred Wegener Institute for Polar and Marine Research, Germany (AWI)

2. Australian Antarctic Division (AAD)

3. IMAS University of Tasmania (UTAS)

Adult krill have a suite of overwintering mechanisms (reduction in metabolic rates and feeding activity, utilization of stored body lipids, omnivorous feeding behavior, slow growth and body shrinkage). Previous investigations in different regions of the Southern Ocean during winter have seldom observed adult krill associated with sea ice. At the onset of winter, when their metabolism is depressed, it is hypothesised that krill migrate inshore to over-winter at depths over 200 m and might be foraging on the sea floor.

Recent findings from both laboratory and field studies indicate that reduced feeding and metabolic activity during Antarctic winter are not directly caused by food scarcity, but represent an inherent overwintering adaptation influenced by the Antarctic photoperiod (day length). It appears that a timing mechanism is operating in krill, and that photoperiod acts as the main Zeitgeber (synchronising environmental factor). The mechanism of temporal synchronisation of krill to their environment is unclear. The influence of photoperiod on the metabolic activity of krill appears to vary with krill age. It is not known at which developmental stage (e.g. one year old krill) the shift of metabolic activity between seasons takes place. In contrast to the adults, the physiological functions that larval krill adopt during winter (reduced metabolism, delayed development, lipid utilisation, and variable growth rates) are under direct control by the available food supply.

PolarTime is an international project funded by the German Helmholtz Association (4 million euro over 5 years -starting January 2013). This project is lead by the AWI (Bettina Meyer) and was designed to investigate the biological clock in krill with respect to their seasonal life cycle. The AAD are partners in the Polar Time project with both the krill group led by So Kawaguchi and molecular group led by Simon Jarman. Krill is used as model organism to study and understand biological rhythms and clocks in other polar pelagic key invertebrates.

 

Hypotheses

1. During SIPEX II (late winter/early spring), the metabolism of adult krill will still be somewhat depressed. We hypothese that adult krill revert to an active metabolic state in spring when light duration exceeds 12h per day.

2. At this time of the year, we also expect to find adult krill more frequently at depths greater than 200m rather than directly below the sea ice.

 

Sampling approach at sea ice stations

We will use two different collection systems to catch adult krill: A large fish pump (see sampling approach of larval krill) and light traps. The light traps are mounted on the CTD rosette (see photo), then deployed into the ocean below the ice to depths approaching 3000 metres. The traps are triggered to close by sending electrical signals down a cable from the ship. Lights inside the traps attract krill. The trap is then closed and returned to the surface.  Cameras mounted on the rosette will also film the sea floor, krill’s behaviour and the operation of the traps.

Standard CDT

Deploying standard CDT

The freshly caught adult krill will be transferred to the ship. They will be examined (sexed and sized) under stereo microscope before being frozen at -80°C for analysis of dry weight (DW), elemental (carbon: C, nitrogen: N), biochemical composition (total body lipid, protein, and fatty acid (FA) composition), stomach and gut contents, and molecular as well as stable isotopic (δ15N) analysis. We will also measure growth of krill and metabolic rates (oxygen uptake and ammonium production rates).

We will use the same approach next year on the German winter voyage WISKY with RV Polarstern on which Rob King, So Kawaguchi, Simon Jarman, Klaus Meiners and others will participate. In that way we can compare our results between regions and years.

Dr. Bettina Meyer, bettina.meyer@awi.de.

Dr. Ulrich Freier, Ulrich.freier@gmx.net

Rob King rob.king@aad.gov.au

Patti Virtue, p.virtue@utas.edu.au

Zhongnan (Molly) Jia, Zhongnan.Jia@utas.edu.au