A deep sea ‘lighthouse’ 2,000 to 3,000 m below the sea ice will be used to lure Antarctic krill into a research trap during a spring sea ice voyage departing Friday.
The light trap is designed to capture live krill on the sea floor to use in experiments on growth rate and metabolism and to learn more about their diet, population structure and winter survival strategies.
Australian Antarctic Division krill aquarium manager, Mr Rob King, says if the trap works, it will be the first time live krill have been collected from the ocean floor at depths approaching the abyssal region.
‘We want to collect the krill to understand how they survive the winter,’ Rob says.
‘Recent footage of krill on the sea floor, filmed by deep-sea cameras, suggests that they may be feeding on marine snow — the debris raining down from above — and other sea floor fauna. We want to get a sample of these krill so that we can compare them to krill living in the sea ice above. Are they the same population and how do they compare in terms of what they eat, and their growth and metabolism?’
Rob and Antarctic Division instrument and electronics technicians customised the light trap to attach to a deep sea oceanographic instrument — the conductivity, temperature and depth (or CTD) rosette. Cameras will also be mounted on the CTD to film the krill being trapped.
‘This footage will allow us to know exactly where and on what kind of habitat the krill were caught,’ Rob says.
‘This will enable us to relate the condition of the krill to the habitat in which they were caught. For example, in the past, egg-laden krill have been observed at 3,500 m depth but it was not possible to sample them.’
The cylindrical light trap works by beaming a light from the top, down onto a prism. The prism reflects the light out of four small, open windows, much like a lighthouse. In theory, the krill will be attracted to the light and will swim through the windows. Once inside the cylinder they will encounter a funnel that directs them into a chamber from which escape is unlikely.
‘The trap’s entrance funnel is very similar to eel traps that Indigenous Australian’s have used for centuries,’ Rob says.
‘We don’t know yet whether the krill will be attracted to the light, but there is some evidence from deep sea cameras that they will be. And hopefully they will survive the 2,000 or 3,000 metre vertical lift back to the surface.’
Tests of the light trap in the krill aquarium were a success. But there’s no guarantee that there will be any krill to sample in the trapping zone.
‘We don’t know if our light trap will work and we don’t know what density of krill we’ll be able to sample. But the light trap is just one tool in a quiver of equipment we’ll use and hopefully one of our approaches will work,’ Rob says.