Supercooling sea spiders

Lloyd Peck of the British Antarctic Survey explains how some creatures in the Antarctic, like sea spiders, grow to giant sizes!

Chris -   Lloyd, so, you work in Antarctica.  It's not very Antarctic in here today.  In fact, it's approaching 9 million degrees because we've had to turn the aircon off, but tell us about your work!

Lloyd -   I've got a group that works in the Antarctic and some of those people there now, at Rothera station currently, it's over 30 degrees here and where there now, it's between about minus 15 and minus 20.  So, there's almost a 50-degree difference between where I do most of my work at the moment and the temperature we have here.  I'm really interested in how animals not only survive in low temperatures, but actually thrive in those environments and why they are different and how different they are, and I have some examples of that.

Chris -   When you say you've got some examples of these animals, what have you got with you there?

Lloyd -   Well, some of the animals and some of the adaptations that we have in the Antarctic are very unusual.  So, one of the best examples I guess is, there's a group of animals that live around the coast of the UK and you've all been on holiday to the seashore.  You've all looked in rock pools and there are animals in those rock pools called sea spiders.  One of the biggest sea spiders in the UK is that animal there.

Chris -   Hang on.  That's your...

Lloyd -   That's on the end of my finger.

Chris -   ...index finger.

Lloyd -   Yes.

Chris -   And there's a tiny speck that you stuck on the end of your finger.

Lloyd -   It's sitting on the end of my finger.  It's about 5 mm across and okay, its legs are curled up so that when it's up and walking around, it's maybe as much as a centimetre across.  And if you've looked in rock pools around the country, you will all have seen this animal.

Chris -   So, what does it actually look like if we sort of put a magnifying glass on there?  What do we see?

Lloyd -   They look like an 8-legged spider.  They look a little bit more chunky than most spiders.  Their legs are a little bit thicker.  Their bodies are a little bit more chunky than that but they do look a lot like a spider.

Chris -   Are they really spiders?

Lloyd -   No, they're not spiders.  They're a related group to spiders.  Say, there's a big group of animals generally called - the scientific name for them is chelicerates.  But in that group, you've got scorpions, terrestrial spiders, and sea spiders.  They're called chelicerates because these organs hanging down under their bodies that are hooked that are called cheli.  Our sea spiders use those chelis to carry their eggs around while they're developing their eggs.

Chris -   But, they don't make webs in the sea.

Lloyd -   They don't make webs in the sea, no.  There are some terrestrial spiders that live in the sea.  They live subtidally and they pull air down from the surface and make little bubbles on the seabed and live in those with their webs.  But these are sea spiders.  They don't do that.

Chris -   But that's not - if I'm honest - and don't take this the wrong way,  that's not very impressive as a specimen.

Lloyd -   That's one of the biggest European sea spiders.

Chris -   Well, that's what I mean.  It's not very impressive.

Lloyd -   Okay, now we have sea spiders in the Antarctic.

Chris -   Okay.  [laughter]

Lloyd -   Now, this sea spider is about 20 cm from leg tip to leg tip and it's not one of the biggest sea spiders from Antarctica.  The biggest sea spiders in Antarctica grow up to 50 cm from leg tip to leg tip.

Chris -   I mean, to be fair, that's the size of a dinner plate.  That's big.

Lloyd -   My dinner plate's are bigger than this, but it is the fair size.

Chris -   Big eater...

Lloyd -   Okay, it's a big animal, yeah.

Chris -   Certainly, it is.

Lloyd -   The biggest sea spiders in Antarctica are 3,000 times heavier than the biggest sea spiders in Europe, around the UK, in North America, in all the temporal latitudes.

Chris -   What does that eat?

Lloyd -   This species eats limpets.   They chase limpets around the seabed.  They catch limpets and they eat limpets.  They have a proboscis that they push under the side of the shell and they eat the limpet from underneath.  But sea spiders eat lots of different things depending on the species.  

And the reason they get big is because it's cold.  The cold allows them to get a lot bigger for two reasons.  One is that you need to spend energy to keep your body alive.  The bigger your body, the more energy it costs.  But when it's cold and you're a cold blooded animal, your metabolic rate is very low because the low temperature pushes your metabolic rate down.  So, the cost for each piece of tissue is a lot less.  The metabolic rates of these animals are 30 times lower than similar animals in the tropics.

Chris -   Does it also help them Lloyd, the fact that because it's really cold, there's so much oxygen in the water because when the temperature of water is lower, you can dissolve more gas in it when it's hot, can't you?

Lloyd -   There's roughly twice as much oxygen in a litre of seawater in the Antarctic as the tropics.  So, there's more oxygen available to fuel your metabolism.  The metabolic rate is lower, the costs are lower, the two trade-off together to make much bigger animals in some groups.  We have a group of animals that were related to wood lice, isopods that grow up to about 14 or 15 cm long.  It's another group where we see giant size.  So, gigantism is one thing that happens at low temperature.  It also means because their metabolic rates are low, that if things go bad, they can just sit and wait.  We've done experiments with some predatory snails offering all the food types they like and some of them have eaten nothing for 3 years - and they're still walking around the tank, they're still reproducing, they're still interacting with each other.  The average number of males was one male every 11 months.  So, if things go bad, you can just wait for them to get better.

Chris -   I mean, that's nearly as bad as a Cambridge University student.

Lloyd -   Well, the alcohol is not available for our animals in the aquarium, but the food is limited, yeah.

Chris -   Are there any other animals that are also huge like that or are these the exception?  Is this sort of the rule down Antarctic?

Lloyd -   Sea spiders are one of the best examples that we have and there are no lobsters and that type of animal in the Antarctic to be predators.  So, sea spiders have radiated out and there are lots more sea spider species in the Antarctic and elsewhere.  We have 10 legged groups and 12 legged groups that you don't have anywhere else.  But there are other groups.  We have ctenophores, sea gooseberries that look like gooseberries in most oceans of the world.  They get up to about 80 cm long in the Antarctic and are much, much bigger than a rugby ball.  So, there are lots of groups that do get bigger, but not everything does get bigger.  There's got to be an ecological reason why large size is an advantage before they do get to that large size.

Chris -   But there've been some reports off the coast of Cornwall recently of these barrel jellyfish that are a meter across.  So, you don't just have to live in really cold water to get big though, do you?

Lloyd -   The biggest jellyfish in the Antarctic are even bigger than that.  I've seen one, 140 feet long and 2 meters across in the bell.  But the size is relative to the architecture of the animal, but also then temperature has an effect on how big that architecture can be.

Chris -   Do they sting?

Lloyd -   Yes, they do.

Chris -   Painful?

Lloyd -   Well, when I'm diving in the Antarctic, it's cold and I wear a full dry suit, so it doesn't matter how much it stings.  It doesn't get through the dry suit and I've never handled one with gloves off, so maybe.  I don't know.

Chris -   I think you should try, Lloyd.  Any questions for Lloyd so far?

Bob -   Hi.  I'm Bob from Godmanchester.  Thinking about temperature and keeping warm enough, how does being in the sea compare to being up on land in the Antarctic because up on land, you've got the wind, but under the water, you've got the water around you rather than air which is better at sucking the heat out of you?

Lloyd -   You're absolutely right.  There are very different adaptations on land and in the sea.  If you're a warm blooded animal then heat loss is a big problem at low temperatures.  Most animals, most of the warm blooded animals, the seals for instance use fat as an insulator.  The fattest animals on the planet are in the Antarctic.  The elephant seals are maybe 45% fat and the biggest elephant seals are 3 tons.  So, that's 3 times the biggest shire horse you've ever seen.  And they keep warm by having lots of fat.  If you're cold blooded then you're the same temperature as the environment.  In the sea and on the land, that's a very different problem because the land gets down to certainly minus 20, minus 30 and you have to be able to survive those low temperatures that you don't have in the sea.  You'll also have dehydration as a problem.

Chris -   We're talking about really cold stuff.  You've got in your experiment.

Lloyd -   Yeah, so animals on the land, really good question, have lots of ways of surviving really cold temperatures.  One is to use anti-freeze, but we have an example of another mechanism here and what I want is somebody from the audience to come out and stand close to where we are now.  Can we have a volunteer?  Come on.

Ginny -   Yeah, got someone over here.  What's your name?

Jessica -   Jessica.

Ginny -   Jessica, okay brilliant.  If you come and stand with me here.  So, I can see a big machine there that's making quite a lot of noise.  What have you got going on here?

Lloyd -   Well, what we've got is, we've got a chiller, a cooling unit.  In that cooling unit, I've got some beakers with a liquid in.  Here's a colourless liquid and what I want you to do is tell me what that temperature says on our thermometer that's in one of our beakers.  There's a minus...

Jessica -   27.

Lloyd -   Oh no, 2.7.  There's a dot.  So, the temperature in this beaker is minus 2.7.

Ginny -   So, what does that look like?  What can you see in there?

Jessica -   It looks like water.

Ginny -   Is it water?

Lloyd -   So, what happens to water when you take it down to minus 2.7?

Jessica -   It turns into ice.

Lloyd -   Is this ice?

Jessica -   No.

Ginny -   He's just drunk it.

Lloyd -   Do you want some, Ginny?

Ginny -   Go on then.  I'm not sure I believe that it's water because if it's minus 2.7, that's definitely still a liquid.  That shouldn't be happening.

Lloyd -   It should be ice, shouldn't it, but it's not.  You could try some and drink some and tell me what you think.

Ginny -   Okay, it's definitely water.  It's not vodka.  I thought you might be tricking me.

Lloyd -   No, okay and it's minus 2.7.  So, if I drop a piece of ice inside, you can start to see that ice grows in the water around the piece of ice.  Can you see that?

Jessica -   Yeah.

Ginny -   So, what can you see around the ice?

Jessica -   Spikes.

Ginny -   It looks like little spikes are coming out from the ice and the piece is getting bigger, isn't it?

Jessica -   Mm-hmm.

Ginny -   You dropped in a tiny weeny piece of ice and now, the ice is almost kind of half-filling the beaker.  What's happening?

Lloyd -   You can see ice growing before your very eyes in the water.  Shall we do that again?  Here's another one, minus 2.7.  Do you want to tell people how fast the ice grows when I drop this little piece of ice inside?  Here we go.

Jessica -   Very fast.

Lloyd -   So the question is, what's going on?  The answer is, this is called supercooling.  If you take water out of your taps and put it into your freezer, it freezes at 0 degrees.  The reason it freezes at 0 degrees is, there are lots of impurities in the water that ice crystal starts to grow on.  

If you take all of those impurities out then there's nothing for the ice to grow on and the ice won't grow as quickly.  You can get the purest water we can get.  You can get down to about minus 40 before it freezes.  

This is water from my lab.  For this, technically it's called 18-mega ohm per cm water.  You measure purity of water by its resistance to electricity as it gets purer and purer, and this is really pure water.  I can get this down to about minus 6 before it freezes.  So, this is supercooling and some animals use supercooling to avoid freezing in the Antarctic in the winter.  They get rid of all the ice nucleators, all the particles that ice can grow on.  They throw them out of their body and that drops their freezing point by maybe as much as 5 or 6 degrees and you add anti-freeze to it and they can then go down below minus 20, maybe down to minus 30 before their bodies freeze.  Thank you very much for coming up.

Ginny -   So, what kind of animals use this?

Lloyd -   The best known animals are very small insects, microarthropods - things called springtails and mites and they're the real Antarctic terrestrial animals, the biggest Antarctic terrestrial animal that lives there year-round, is about 2 mm long and it's a mite or a springtail and they use supercooling and anti-freeze to survive down to about minus 35 degrees and they can survive in the crevices during the Antarctic winter, protected a little bit by snow from the minus 50s and 60s above.

Kelvin -   I'm Kelvin from San Francisco.

Chris -   Gosh!  You've come a long way.

Kelvin -   I have and since my name is Kelvin, I think it's very appropriate that I ask this question.  Is there any way for us to do this at home, so for example, by distilling water?

Lloyd -   If you can get your hands on any really pure water, yes, you can.  Your problem is going to be getting it low enough so that it's below freezing and getting it at exactly the right point.  The equipment I brought in here will run at minus 3 degrees all day which means I can set it up and running.  If you put it in your freezer, it's going to go - because your freezer is going to be at minus 18, your timings gonna to have to be good.  But I've done this at home in the freezer and I bought ultrapure water from the chemist and it works.

Chris -   Excellent!  Any more questions?

Kate -   My name Kate Bacher.  I'm also from Godmanchester.  You were talking about anti-freeze.  Is that anti-freeze as we would know it that we put in our cars?

Lloyd -   It's not the same as you would put in your cars, but there are lots and lots of chemicals that are used by animals as anti-freezes.  There's a whole range that are used by fish in the ocean that are proteins and glycoproteins.  Insects have a barrage of anti-freezes, glycerol they can use and they have a whole range that will allow them to survive very, very low temperatures.  They don't use glycol.  Ethylene glycol isn't one that they commonly use, but they got somewhere between 50 and 80 different anti-freeze molecules.  There are a couple of moths that can turn their bodies into 60 or 70% glycerol for the winter time to survive in a kind of semihibernation state over a long period of time and then when the temperatures come back up, they can resynthesize it back into the functioning molecules that they need.

Chris -   Georgia, you've got something.

Georgia -   Mark Shiverett on Twitter wants to know, "Are there any antibiotics or other natural products which come from the sea?"

Lloyd -   There are lots and lots of natural products that come from the sea.  So, there are alginates that are used in ice creams and there are many products, but I don't know about antibiotics.  I suspect there are because I suspect that some of the animals that we have in the sea and some of the bacteria that we have in the sea all interact and lots of them have chemical defences.  Some of those chemical defences will have antibiotic properties.

Georgia -   So, what are these products which go into ice cream?

Lloyd -   Well, alginates for instance...

Chris -   I see which way Georgia' mind works.

Lloyd -   Yeah, there are several low temperature products that are used to keep things slightly plastic in their makeup and they're used to help control the size of crystals when ice grows.  And so, if you control the crystal size very carefully, you can make a smoother ice cream.  And so, those products are used for those sorts of things with ice creams.

Chris -   Ladies and gentlemen, Lloyd Peck from the British Antarctic Survey...