How do krill survive

Factors that may affect their numbers include such things as global warming, sea ice area, competition with other species, possible over-fishing in the future, and of course the ozone hole.

Surprisingly, it is only recently that the possible effects of UV on Antarctic krill have been examined in any detail. However, my first finding was somewhat alarming. I found that krill in captivity are remarkably susceptible to UVB, which killed them in under a week. The levels were quite low, similar to those seen at metres down. Then a friend of mine revealed krill DNA to be more prone to UV damage than any other animal yet examined and the story got more interesting overnight.

But there was something else going on out there in the oceans. If krill are so fragile around quite low levels of UVB, how come there are so many of them in the southern ocean? So how do the krill deal with all this? One possibility is that they simply go deeper, for UVB gets weaker the deeper it goes.

But to respond to something, you have to be able to sense it. So I asked the question: can krill react to UVB? After hours of watching krill react to different strengths and gradients of UV radiation in horizontal and vertical fish tanks, the short answer to whether they react to UVB is:.

When put under UVB krill behave as if nothing is happening when in fact they are slowly having their cells, membranes and DNA damaged. This was a worry until we tried UVA, and found that krill do indeed react to UVA by either swimming away or going deeper. Why waste effort? We have shown that there is very little food within the ice but nevertheless the larvae persist in scraping away at the surface as there is quite literally nothing else to do.

This is thought to be for predator avoidance as well as entrapment of food released from the ice above. Big stretches of dead flat sea ice usually had very low larvae numbers, the high concentrations we observed were in the shelves and caves in the complex rafted ice. This has the effect of immediately separating them from the piece of ice that they descended from that evening, at sunrise they will come back up under a different piece of ice, potentially some that has not yet been heavily grazed, therefore providing more food for them.

Our models show that their movement being carried along on the ice flows during the day together with their movement when in the water currents under the ice at night overall adds to propelling them towards the marginal ice zone MIZ. This zone is much more productive than the pack ice zone with more chlorophyll.

As the season approaches late winter or early spring, due to increasing ice temperature, the surface of the sea ice begins to melt and it starts to release materials that were locked in the ice during the period when the ice froze and this allows the larvae access to this material.

Ice algae also start to grow as the light level increases. So I would see the animation looking something like larvae tucked away on a shelf under the ice, grazing away like a flock of sheep, with a sun high in the sky above them.

The sun then sets and exactly at the time the sun sets the larvae all herd off the ice shelf like lemmings and swim down into the upper 20 metres of the water. As soon as they get just below the sea ice you show the larvae being carried along below the ice by the currents.

Whereas adult krill are truly pelagic, they can swim both vertically and horizontally. So for the entire time the sun is down you show the pattern of ice flows above the larvae changing. And last year we sailed across one school of krill that was , tonnes in one school, about a nautical mile wide. In fact, construction has started on this wonderful new ship already, and Rob, I know you've had a lot to do with the design of the ship to enable it to really be the foremost ship for krill research.

What kind of things have made this ship special for krill work? When we go to Antarctica, the sea is frozen over with solid ice. This ship has doors that open in the bottom of the hull, so you can lower equipment, remote controlled vehicles, nets, and all sorts of things, into the water and take samples.

Plus, we have a wet well where five tonnes of water every minute will flow through pipes into there, to filter out krill and plankton. So, this is a feature that no other vessel has ever had, so we're really excited to work there.

We've just been looking at our new Icebreaker, and one of the exciting things we're doing with the Icebreaker is we've been looking for a new name. We've had a big competition, where school kids all around Australia have contributed, and we'll be getting close to announcing a new name, and the schools who have contributed the winning name will be able to send some kids with us, this coming summer, down to Antarctica.

So, if any of you have any questions as we go through, please send them through. We'll do our best to answer them as we go, and I know Rob will go online after we're finished going live here, and answer some more of your questions. One of the really interesting things around krill is that a lot of animals depend on eating them for their own lives. And here at the Antarctic Division, we have scientists working on krill and also on the very largest of animals who eat them.

So, Dr Elanor Bell is one of those people. Do you want to tell us a little about the work you do, and especially how it is you get an insight into how whales live in the Southern Ocean and interact with the krill? Absolutely, Nick. Well, as you've just said, whales are the largest creatures on the planet, and one of the biggest species we work with is the Antarctic Blue Whale, which can grow up to 30 metres long, and they can eat up to three tonnes of krill in one day.

So, Rob, your krill are in big trouble. What one of the exciting things we do is, we can use technology, such as satellite tagging, to track whales and work out where they're going to find their food, how deep they dive, how often they dive, what type of krill they're targeting. And we were putting out satellite tags on the Minke whales, and again, looking at information about how they were using the krill, where they moved to get it.

But the most exciting tag we put out was a video suction cup tag. So, we can watch them with their huge mouth engulfing swarms of krill, swallowing the krill down, and then we also get information about then how they're interacting with other whales and the environments. So, if you have any questions, please send them through and we'll be doing our very best to answer them.

On our way to the Krill Aquarium, we're going to be talking a bit around how krill fit into the whole marine system. So, Rob, you've had a lot to do with this sort of work over the years yourself. Yeah, I mean the work we're doing in the lab that we're going to see shortly, is all about getting data to put into things called models, and models are really how we predict the future.

Yeah, definitely. So, Nick, the eco-system is literally everything. And so, krill are particularly important in the eco-system, partly because so many things eat them, including whales, but also seals and penguins, and a whole range of other species.

They play a role in recycling nutrients that are then important to the phytoplankton that they eat. All right. And so, my understanding is then that you use models to try and work out all those interactions, and how they live in that environment. So, a model is literally a simplification of reality. And the kind of models that we use in our work are mathematical models that again, are simplifications of this really complicated real eco-system.

And in fact, they're the only tools that we have available to try to peer into the future and ask questions about the way that eco-system might respond to changes in the environment, or to changes in the way that humans interact with it. So, they're really important. So, you sit at your desk, you do all this clever work with these eco-system models, have you ever actually been down south on the ship and had a look at the krill, so you can see them in the wild? We're dropping out a bit now, so for those of you who have just joined us, you're at the Australian Antarctic Division in Hobart in Tasmania.

We're doing a tour of the —. Okay — for those of you, thanks for your patience, we're just having a couple of drop out problems, and we're at the Australian Antarctic Division here in Kingston in Hobart, having a tour of our facilities, and we're about to head down to the Krill Aquarium.

We've got krill expert Jess Melbourne-Thomas and Rob King with us, and we'll be meeting another person before we get down to the krill. So, Jess, thanks so much for talking to us about your work. See you later. I mean, these guys run when they see me coming because they're just so useful these people. This is an electronics engineers, instrument technicians, marine science gear offices, and together they build the gear that we can ask questions that have never been asked before.

And then we bring the data back and analyse it. So, we really do rely on them. But we'll be getting to answer some of your questions in just a moment. We might just pause here in the corridor for a moment, because we've got some beautiful photographs, taken with a scanning electron microscope of tiny little animals.

Do you want to tell us a bit about them, Rob? So, some of these are the phytoplankton that form the base of the Antarctic food chain. So, this is what krill are eating. Maybe different species of these floating around the Southern Ocean, photosynthesising and putting all that energy from sunlight into joining water and carbon dioxide together, to make complex organic molecules, and that is the start of the whole system.

Sure Nick. And some of the most important decisions that we do make every year are around how we manage the fisheries, including the krill fishery, and make sure that the amount of krill that the fishing vessels take out of the marine environment, make sure that we allow for the needs of the penguins and the seals, and the whales, and all the other animals that rely on krill for their survival as well.

So, as I said, there are 25 member countries, and we have all of those countries turn up every year, and a whole bunch of other stakeholders as well, both the fishing industry and environmental organisations who are really passionate about the Antarctic environment. Great, thanks Gill. We've got a question I see coming in from Sacred Heart in Geelong, and they want to know how do krill survive in water at such very low temperatures?

Rob, you're the expert. If we jumped in the water at that minus one degree temperature, we would find ourselves freezing to death within five minutes or so.

All their enzymes work best at that temperature. If you try and keep krill in an aquarium above about three or four degrees, they start to go downhill quite quickly. So, everything about them is adapted to that because they've made gradual adjustments through time and evolution. So, we got an aquarium set up here at the Antarctic Division Rob, and I know you've been involved with this pretty much from the start. Do you want to tell us a little about what we're about to see?

Yeah, so this aquarium replaces one that was really a rudimentary aquarium, that was just built into a cold room in the s. That was when we were using the Nella Dan as our research vessel, so even before the Aurora. So those very first experiments we ran were in fridges, but this aquarium was purpose-built for krill and runs at 15 degrees for us, but —. Why do we actually keep them all the way up here in Hobart, so far from their normal area where they live?

You can do the best research in the field. Every scientist wants to work on their animal in the actual field where the animal lives. So, what we do is bring the krill back here and have the best of both worlds.

By bringing them here, we can have scientists fly in from anywhere in the world, land here, do research on krill, take their data and publish it. We can have a turnaround of a few weeks, from collecting data to sending off to a paper for peer review. If you try and do that in Antarctica, you're looking at a two to three year process.

And what are these amazing tubes, these great big — they look like a sports drink collection. What are these Rob? Well this is a sports drink for krill. This is Antarctic phytoplankton — you're looking at two different species here. But we're growing this and taking maybe 30 litres of this out every day, to pour into the krill as their food.

So, these are live versions of what we just saw on the photographs on the wall down the corridor. A question has just come in from Christine, asking what about krill and climate change?

Are they likely to be affected by climate change? Yeah, we believe they will be because krill are living in one of the areas that is showing the greatest hot spots for warming that we've seen on the planet so far. And krill really do rely on having that ice and that phytoplankton where they're expecting it when they need it — when they hatch out from eggs and they need to start feeding when they get to the surface.