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The Planet Earth podcast - 'Fish poo, dead whales, and the Japan earthquake'.

23 March 2011

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The Planet Earth podcast - 'Fish poo, dead whales, and the Japan earthquake'.

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Hello, I'm Richard Hollingham, welcome to another edition of the Planet Earth Podcast. This time I'm in Exeter to investigate the connection between fish poo and the white cliffs of Dover. We'll also be meeting a scientist who studies dead whales.

Researcher's voice: When a whale normally dies it may gas up and float around for a bit and once those decompositional gases have left the body the carcass will sink to the seabed.

RH: So here's an intriguing question. Could the white cliffs of Dover have been formed from fish excrement? It's certainly a real possibility based on new research carried out here at the University of Exeter, led by Rod Wilson. I'm in the tropical aquarium; it's really pleasantly warm, a bit of a damp tang in the air, tanks of brightly coloured fish around me from the floor to the ceiling. And Rod is with me – Rod, what were you investigating?

RW: A little while back we discovered that rather surprisingly marine fish are major producers of a mineral called calcium carbonate within the oceans. Previously it was known that coral reefs, for example, produced lots of this white, crystalline mineral, and lots of marine algae do it to. But no one had really addressed the issue that fish produce it, and they simply precipitate these crystals within their gut and then excrete them to the external environment.

RH: So what's going on inside a fish gut to make these?

RW: Well fish are obliged to keep their water balance in check to drink lots of seawater. So your average fish might be drinking the equivalent of 12 litres of fluid a day compared to an adult human. And as part of the processing of that fluid, they precipitate calcium ions which are present in abundance in sea water as calcium carbonate, and they do this by producing lots and lots of a basic material called bicarbonate into the gut and any ingested calcium ions get precipitated as this mineral crystals of calcium carbonate. That in tern helps them to absorb water through a very interesting mechanism and also prevents them absorbing the calcium which would otherwise be potentially toxic.

RH: And how tiny are these crystals?

RW: Individual crystals are very tiny. They're one to two microns long in some cases, which is a 1000th of a millimetre. But what happens is they aggregate together and you'll get up to a million individual crystals in a small aggregate which is then visible – maybe half a millimetre long – and then that, or lots of these, get wrapped up in a mucous coating and excreted to the external environment via the gut.

RH: And you were tracing these and looking at their effect on that external environment. How on earth do you do that?

RW: The first place is to collect fish from the real environment, and we did this particularly study in the Bahamas at a place called Cape Eleuthera Island. Brought wild fish into the laboratory, waited for them to excrete these products and collected them from the bottom of the tanks and then we begin the analysis. First we clean up all the organic mucous, very simple, you use household bleach and what you're left with is the crystals of calcium carbonate. Then you can measure them quantitatively, or bring them back to the labs, in our case in the UK to a colleague in Manchester, and look at them under the scanning electron microscope so you can study the shape of the crystals and also the mineral type within that.

RH: And you're interested in what contribution they make to geology really, to the landscape?

RW: Yes, certainly the next step is to ask that question. But the reason we went to the Bahamas in the first place is because our predictions up to this point were that the crystals produced by fish are likely to dissolve quite quickly once they leave the body and enter the oceans. But then we realised that there are some parts of the world where there's a strong likelihood that they might actually be preserved in sediments and those places to look were warm, ie. tropical, and very shallow because the depth actually affects the dissolving of this mineral too. So we picked the Bahamas as a very likely place where we get lots of fish, lots of calcium carbonate sediment, and the right conditions for it to be preserved.

RH: Now also here is Erin Reardon. You're looking at this not in the Bahamas – she shakes her head sadly! – but in the UK.

ER: That's right. We're just getting started and we're doing a similar thing. We're targeting a range of species from a range of different lifestyles and habitats, collecting the material and then we're also working with a range of different scientists so find evidence of these crystals in the sediment. So it's like looking for a needle in a haystack so far.

RH: But again you're interested in what contribution they make to the sediment?

ER: That's right. We basically want to know what happens when these carbonates leave the fish. Are they dissolving, are they contributing to the sediment? And we just don't know what's happening here in the UK.

RH: Which brings us back to the white cliffs of Dover. Do you really think that they could have been formed by fish?

RW: They're certainly not only produced by fish and in fact people have studied places like the white cliffs of Dover chalks and limestones for a long time and within that they're particularly looking for microfossils of things like coccoliths, which are very beautifully shaped shells on single celled organisms. What we're saying is there's quite a possibility that all the surrounding mush that they haven't really been able to identify previously, of which is about 50 per cent they don't know what it is, could potentially have come from fish because it's of a similar grain or crystal size to fish, and we're yet to actually analyse that.

The data from the Bahamas is very interesting because it's the first ever evidence of fish carbonates being found in nature and preserved within sedimentary material. And of course places like the white cliffs of Dover and other chalk and limestone rocks ultimately form by sediments settling out in very shallow areas of the ocean over geological time, becoming compressed and then they become chalk and limestone. So the next step will be to ask, well could fish from the ancient past have ever produced sufficient amounts of this material to actually make a major contribution to the limestone and chalks we see today? Some further evidence to point towards that, is that if you look at ocean chemistry and atmospheric conditions from say 100 million years ago in the middle of the Cretaceous period – and we know that there were plenty of fish around then – then every single factor that was different then we know from evidence in the laboratory, would have caused fish to produce a lot more calcium carbonate and of a type that's much more likely to be preserved in sediments. So it was warmer then, it had higher carbon dioxide in the atmosphere which we know enhances production by the fish, and most importantly the calcium concentration in the dissolved sea water that the fish are drinking was at some point four times more concentrated then than present day. So you put all those things together and you have a recipe for a massive, massive elevation in the amount of calcium carbonate fish were producing 100 million years ago and the next question is, would that turn up in today's rocks?

RH: And that's what you're trying to find out?

RW: Well, we'd love to get some more funding to look at that in the future so yes.

RH: Rod and Erin, thank you both very much and we'll come back and talk to you again Erin when you've done your research. And you can read more about the research on the Planet Earth Online website and see some pictures of the aquarium here in Exeter on our Facebook page. You can find both by searching for Planet Earth Online.

Earlier this month a 14-metre-long sperm whale died on the coast of Kent after becoming stranded on Pegwell Bay. Centuries ago a beached dead whale was worth a great deal and would automatically belong to the Crown, but that right has now passed onto London's Natural History Museum. And a whale carcass, for scientists like Nick Higgs, provides a valuable opportunity for study. Nick works, in partnership with the museum, at the University of Leeds, and as soon as he was told about the whale, headed to Kent to collect a sample for his research. Sue Nelson found out why. It's a tale of all creatures great and small.

NH: I'm interested in how whales become fossils. Everything that happens from when they die to when we find them in the rocks.

SN: I assume that most whales die at sea so what's the difference in having a carcass from a whale that's been beached, like the one at Kent?

NH: When a whale normally dies it may gas up and float around for a bit, and once those decompositional gases have left the body the carcass will sink to the sea bed and this is a massive event for the deep sea animals that live down there – something we call a whale fall. And it attracts a huge number of scavengers from sharks to hagfish and hundreds of amphipods – these shrimp-like animals that specialise on feeding on the flesh – as well as spider crabs that also come to have a pick at the meat.

SN: You're interested in a specific creature in particular aren't you? Which one's this?

NH: Well once all the meat's gone, you're left with the skeleton but the feast isn't over then. I'm interested in these worms that come along to specifically feed on the whale bones. They're called osidax worms, which means 'bone devourer' in Latin. They range in size from about the size of your finger to maybe the size of one of your joints. They look more like little palm trees really. They have what we call roots that grow into the bone and dissolve it away and eat the bone, and then they have this long trunk which sticks up out of the bone, and out of that trunk are four palps which are kind of like palm tree branches but they're bright red to pink and those are the gills of the animal, those are how it gets oxygen out of the water.

SN: When you went down to Kent, you got the call, you went to see the stranded sperm whale. What did you get out of it, or what did you want from it?

NH: Well, we were going down to get some bones that we could put on the sea bed to try and find some of these osidax worms and we came back successfully with a whole flipper which has got several nice bones in it that the worms like.

SN: And where is this flipper at the moment?

NH: The flipper's stored at the Natural History Museum at the moment awaiting deployment in the deep sea.

SN: Meanwhile Nick can also study the effects of osidax worms in the palaeontology clean room at the university. And the bone samples, which are preserved in alcohol, don't always need to be from whales.

[i:Sounds of doors opening.}

SN: Several jars here, the sort that you'd expect to see a lot of chutney in. Sponge-like in appearance, although one of them, that does look like what you'd expect to see of a bone.

NH: Yes, that's actually the leg bone of a cow. It seems that they'll live on several different types of bone. They're quite happy living on any old bits of bone.

SN: And these two jars then, with the more sponge-like appearance – if I can read that, that's it's an elephant seal vertebra and what's in this one?

NH: That's the top of it that we've cut off to get it into the jar. This was from an elephant seal carcass that was put down in the same area that we previously sank the whale carcasses to see if these worms would like the bones of other animals as well. So we're starting to think that they might have a much bigger impact on the fossil record, of not just whales but any marine vertebrate.

SN: Let's take a couple of these jars, back out of the clean room, away from the noise of the fume cupboard and into the lab. What am I looking for? I'm not going to see any worms in this, am I?

NH: No, you may just see some of their tubes hanging out of the bone because they tend to dry up in the alcohol. They don't quite look as magnificent as they do in real life but can you see here these parchment-like bits sticking out of the bone? Those are the tubes.

SN: These tiny little tubes, that almost look like rolled up spider webs.

NH: Yeah, they've kind of decomposed because they've been in the jar for so long. You can see there are several small holes on the bone and I don't know if you can just tell if I change the light slightly, there's a kind of mottled colour to the bone surface. That's the extent of where they've bored away the bone underneath the surface. So all that black area is where the bone has been eaten away.

SN: Why is it so important to know the effect that your bone-eating worms have on a whale? Is it purely so that you know that you've got the correct age of a whale fossil or is it more basic than that? Do they have such an effect on it you can't necessarily tell what the creature is or when it was from?

NH: Exactly. Within ten years they may be able to eat away whole bones so in which case we'd have no record of that whale ever existing. Whereas in some whales, like the one I'm investigating in Italy, a lot of the bones where found and couldn't really be properly described because they were so mangled and partially destroyed by these worms. And what I'm really interested in is figuring out whether the gaps in the fossil record of whales may be caused by these worms. There's a significant period in the evolution of whales when they become ocean-going, when they move away from shallow habitats. And we get this gap in the record that is incredibly tantalising because at the next stage after this gap you start to see what we know as the ancestors of modern whales – the tooth whales and the baleen whales – but there's this tantalising gap when they started moving out into open water which is exactly when the carcasses would have started arriving in the deep sea. So, are these worms responsible? We don't know.

SN: And the only way to find this out then is to see a carcass in its entirety in situ on the sea floor. How easy is that?

NH: It's very hard and in fact that's only happened a few times when we've found natural whale falls on the seabed. What we do is we tend to sink carcasses that wash up so we know where they are and we can go back and study the process in its entirety.

SN: It sounds like you need a series of fortunate coincidences from a scientific point of view so you get a whale and you can immediately transfer it to somewhere that you can study.

NH: It is. It's immensely coincidental. All we can do is get everything ready and then sit and wait. When one already dies and washes up then we try and make the most of that opportunity. And it's not always possible, in which case we'll just try and get some bone samples or whatever we can. And in fact most of the whales that wash up go to landfill or are incinerated which is such a shame because we can learn so much from them even though they are already dead, and what we'd like to see is them sank at sea so we can find out more about this process.

RH: Nick Higgs from the University of Leeds. And in a couple of months he'll be travelling to California to visit whale carcasses sunk in the sea. You'll be able to hear how he gets on in a future edition of the Planet Earth Podcast. As I speak the situation and the aftermath of the earthquake and tsunami in Japan seems to be becoming worse by the day, and as the recovery effort continues geologists have been investigating what caused this latest disaster. I'm joined by Tamera Jones from Planet Earth Online who's been writing about this for the website. Now Tamera, this earthquake was so powerful it was even felt in the UK. Is it clear what happened?

TJ: Well yes, I think scientists are pretty clear about what happened. I spoke to David Kerridge at the British Geological Survey, he's the head of earth hazards, and he was explaining to me that what happened in this particular case was you've got the Pacific plate going underneath the plate that Japan is on, and it's like a conveyor belt at Tesco's, so the Pacific plate is like the conveyor belt and it disappears underneath the Japan plate. And what happens is it sticks as it goes down, and once it stops sticking that's when it springs up and they think it sprung up by about ten metres which is a large amount, and of course that meant that huge volume of water, the ocean above it, moved and that's what created the tsunami.

RH: And that really is the cause of a lot of the damage, this tsunami?

TJ: Yes, exactly. And I spoke to Simon Boxall at the National Oceanography Centre and he was explaining to me that the tsunami is not like your normal wave which is only a few metres maybe in length. This wave can range from ten to hundreds of kilometres in length so it's a massive volume of water. And it was really close to the northeast coast of Japan so when it hit the coast all its energy hadn't dissipated, it just went straight into the land. The wave was travelling at about 500 miles an hour, which is the speed of a jumbo jet, when it hits the shore but of course it has to slow down because it hits all that land, even though its quite low-lying along the northeast coast of Japan. And the back of the wave catches up and it builds up in height and it got to about ten metres in height which is really big, and it went in upto about six miles inland. And of course it hits trees, it hits cars, buildings, and it carries all that six miles into the land, and then it has to recede and comes back. So it's like a double hit really, which is why there's so much devastation and you can see all the damage on the TV.

RH: And what are the geologists doing now?

TJ: Well usually if an earthquake happens on land they can use a technique called INSAR and that means that they can use satellites and the satellite takes images of the land around where the earthquake happened. The INSAR manages to look at where the stresses are and where the future possible hazards are. But in this particular situation, because the earthquake happened under the ocean, INSAR can't look through the water unfortunately. So what they have to do is use seismic computer models, and look at the seismic waves that this particular earthquake generated and say well, if the fault happened this way, if there were particular problems in this fault here, would it create these sort of seismic waves? Or if there was a fault there would it create these seismic waves? And by doing that lots and lots of times they can actually look at where the future hazards probably will be.

RH: Well thanks Tamera. We've got several scientists around the world recording audio diaries about their research and one of them is Sophie Hollis who's in French Polynesia – Pacific islands about 10,000 kilometres from the earthquake. She's just sent us this despatch and I think her experience gives us a sense of the scale of this earthquake and tsunami.

SH: It's 4.52 in the morning and we've just been woken up by the sound of a tsunami alarm so everyone's grabbing their stuff and we're going to jump in the cars and drive up the mountain. We decide to get in the car to evacuate and we're stood by this normally really quiet road and there are cars and cars and cars going past. Everyone's driving up the mountain to get away from the tsunami. We don't know yet how high it's going to be, but we're going to get in the car and get to a high point to be safe.

Sounds of cars and voices, and radio in the background.

SH: So up on the mountain – pretty much the population of Moraya waiting for the wave. Apparently it's 40 centimetres. We're just waiting to hear on the radio when it's going to be safe to go back down.

RH: University of Bristol researcher Sophie Hollis in French Polynesia, who is safe and now getting back to her research. We'll hear more from Sophie about the work she's doing in the coming weeks. And that's the Planet Earth Podcast. I'm Richard Hollingham, thanks for listening.