An international team of scientists has pulled out the ‘big guns’ in experimental krill pumping technology to capture live specimens of the tiny and elusive larval and juvenile stages of this important crustacean in the East Antarctic sea ice zone.
Australian Antarctic Division krill aquarium manager, Mr Rob King, caught larval and juvenile krill in open water leads in the sea ice, using a high volume water pumping system off the side of the icebreaker, Aurora Australis, during the recent Sea Ice Physics and Ecosystem eXperiment-II (SIPEX-II).
The pump, designed originally for salmon by Aqua Life Products in Idaho, US, uses a large, insulated pipe to suck some 400 litres of water per minute into a filter system housed in the ship’s oceanographic instrument room. The captured krill are then gently hosed into a holding tank for transport to the ship’s laboratories.
“The pump is much gentler on krill than the traditional method of catching them in zooplankton nets,” Mr King says.
“Better than 95% of the krill that came through the pump were in good condition and survived. This is the first time we’ve tried using a fish pump in Antarctica and it’s an approach we’re exploring as an experimental technique. It seems to work well but we’re still to determine whether it’s efficient enough to deploy on a regular basis.”
The krill were collected by Australian and German scientists onboard, who are studying their metabolism, growth rate and diet, and the sea ice habitat they live in, to learn more about how these early life stages survive the winter.
“Most krill research has been conducted on adult krill during the Antarctic summer and only a few studies have focused on the larval stages during winter — mainly from the Atlantic sector of the Southern Ocean,” says krill biologist Dr Patti Virtue, from the Institute of Marine and Antarctic Studies.
“We think krill larvae depend on the winter sea ice algae for food. If climate change alters the thickness, extent and duration of Antarctic sea ice, as it is predicted to, this could affect the survival of krill larvae, with flow-on effects to the adult population, and higher organisms that rely on krill for food.”
Krill have 11 larval stages before they become juveniles and then sexually mature adults. The final larval stage caught on the voyage was about 9mm in size and looked much like a juvenile (25mm) or adult.
As well as the heavy duty krill pump, Dr Bettina Meyer and Dr Ulrich Freier from the Alfred Wegener Institute for Polar and Marine Research in Germany used a smaller sled-based pump on sea ice floes, to capture krill from directly under the ice.
Dr Meyer’s previous research in West Antarctica has shown that larval krill prefer the relatively favourable living conditions provided by rafted sea ice — where large pieces of ice push up over each other, forming pockets or icy caverns protected from strong ocean currents. Within these pockets of calmer water, sea ice algae associated with the underside of the ice provide an important food source for the developing krill.
“I want to compare the habitat we’ve observed in West Antarctica with what we find in East Antarctica, to see whether the larvae prefer an over-rafted refuge containing a developed sea ice algae community,” Dr Meyer said.
“In West Antarctica the krill population has shown a strong decline over the last 30 years and we think it has something to do with the survival of larvae over winter.
“Climate change is already having an impact there, with sea ice formation starting much later, when the algal blooms have finished. So there is less algae around to be incorporated into the sea ice and less light to stimulate production.”
Australian Antarctic Division