Krill: The fuel of the ocean
They can shrink, glow and stain penguin poop pink – why this scientist wants you to love krill.
If you’re like most people, you probably haven’t given krill much thought.
You’ve heard of them, of course. They’re the small, shrimp-like animals that live in great swarms in most of the world’s oceans.
You probably know that they’re the primary food source of the largest animal on Earth, the blue whale.
Perhaps you don’t know that seals, ocean birds, squid and penguins eat them too. In fact, some penguins consume so much krill that their krill-stained pink poop can be seen from outer space.
This fact–and many more – can be found in The Curious Life Of Krill, a book-length ode to the strange and enigmatic marine organisms.
It was written by biologist Stephen Nicol, a professor Institute for Marine and Antarctic Studies at the University of Tasmania in Hobart who has been studying a species of krill known as Euphausia superba for roughly 40 years.
But Nicol is more than a krill researcher – he’s also a devoted krill admirer.
His new book touches on elements of krill physiology, ecology and behaviour, but he says his ultimate goal is to “sing the song of the krill”.
“I like krill – and there are only a handful of people on the planet who can genuinely make this claim,” he writes in the preface.
Nicol notes that krill are among the most abundant animals on Earth, and in the Southern Ocean they can assemble in staggeringly large swarms of up of 30 trillion individuals.
Also, they can glow in the dark. And they are amazingly omnivorous, using their combed feeding legs to eat nearly everything in their path. That includes small plants and animals even tinier than they are, both living and dead. Indeed, researchers discovered that the digestive enzymes in their stomachs are among the most powerful on Earth.
Nicol hopes that his new book will inspire readers to praise the “delicate and feathery beauty” of krill, along with “their tremulous and sensitive behaviour”.
“Above all,” he writes, “I would wish that you find yourself liking krill as much as I do.”
Nicol talked at length about how he first became fascinated with krill, their role in the Antarctic ecosystem and their future in the face of climate change. This conversation has been edited for length and clarity.
Why study krill?
When I started my PhD in Canada, I was told there were these spawns of krill that came to the surface in the Bay of fundy and that it was a very spectacular phenomenon. I decided to see what was happening there, and that’s how I met krill. They were really enchanting.
People had thought of them almost as particles in the ocean, but when you see them in their natural environment, you realise they were more like little antelopes of the ocean. That really hooked me.
What do people misunderstand about krill?
That they are actually big – about 6cm across. Half the animals in the ocean are bigger than them, and half the animals in the ocean are smaller.
We have an aquarium here in Hobart where we have been keeping live krill for years. The first thing everyone who sees them says is, “Oh, I didn’t realise they were so big.” It’s uncanny.
What animals eat krill besides whales?
The great whales like blue whales, fin whales and humpback whales were the biggest predator of krill. It is estimated that when they were at their most abundant, before industrial whaling began in the early 1900s, they were eating as much as 220 million tons a year. That’s a lot of krill.
And then you’ve got the smaller whales, seals, sea birds, penguins, fish, squid – all of those depend on krill to a greater or lesser extent. So the poor krill is the target of a lot of predation. It is amazing that they can withstand it.
You write that they can amass in groups as large as 30 trillion individuals. Is that really true?
It’s not easy to put exact numbers on krill, but we know that there are hundreds – if not thousands – of animals in every cubic meter of water in a krill swarm. And if you multiply that up, you realise you are talking about billions and trillions of animals.
Also, they live in the Southern Ocean, which covers about one-sixth of the planet. When you have an animal that is locally very abundant and occurs in a huge habitat, you suddenly start looking at really big numbers.
What are the challenges of studying krill?
I’m sitting at home in Hobart now, and the Southern Ocean is right outside my window. But between here and the krill habitat is this incredibly stormy ocean.
It is the stormiest patch of water in the world. Every time we go south, we have to go through this really bumpy bit of water and we have to sail at least a week to get to where the krill live.
What else makes it hard?
for much of the year there is a layer of ice over most of the habitat where most of the krill are found.
Also, they spend most of their time below the surface, so we have to go looking for them using things like nets, which are very primitive and crude.
We use echosounders as well, and those are getting more sophisticated with time, but very often we don’t know what we are seeing on the echosounder because you can’t see into the water.
I was surprised to learn krill can shrink.
Yes. When we tell people about this they are not surprised. They say, “When I don’t eat food I shrink too.” But it is not quite as simple as that. They don’t just lose weight, they lose length. You can keep krill without food for about a year, and they will be about half the size they were when you started.
The trouble is, we have always used the size of the animal as an indication for how old they are. Now that we know krill can shrink, we know that the smaller animals may in fact be older animals.
Do you think krill will be affected by climate change?
The main issue for krill is likely ocean acidification, which is caused by the carbon dioxide that has been put into the atmosphere going into the ocean. Experiments in the laboratory have shown that the eggs and larvae of krill are fairly sensitive to increased acidity.
We’re actually kind of worried about that because ocean acidification is not something that can be stopped.
Are humans a threat to krill?
Back in the 1960s and 70s there was an idea was we can double the world’s fish catch by catching krill. The idea was that this would provide protein for the starving masses. Well, it wasn’t quite like that.
for a start, it’s incredibly expensive to go krill fishing. The cost of krill fishing is so high because of the amount of fuel required to get down to the Southern Ocean, and there are alternatives to krill products that are much cheaper.
People have desperately been trying to find something useful to do with krill to make a buck, but it’s really tricky.
What more do you want to know about krill?
I’d really like to learn more about their behaviour – their social interactions and responses to features like temperature and light. I think that’s the missing bit.
We know quite a lot now about their biochemistry and their physiology and so on, but we don’t really know much about their behaviour at all.
When we think about how the krill population will react to climate change, some of it will be their physiology, but a lot of it is behaviour. If they are able to detect warmer water and stay away from it, then they will be really resilient. If they can’t, then they are going to be affected badly.
We’ve got some behavioural ecologists who are getting interested in it, so I think that is where the next breakthroughs will come from.