Life and Death in ancient seas

The oceans were the cradle of life on Earth for billions of years before our ancestors took to the land and air. But they have also seen some of the most devastating mass...
11 October 2011


Anomalocaris model


The oceans were the cradle of life on Earth for billions of years before our ancestors took to the land and air. But they have also seen some of the most devastating mass extinctions in geological history. In this month's Naked Oceans we find out about the bizarre evolutionary experiments that appear in the first explosions of complex life over 600 million years ago, and what may have driven the catastrophic End Permian extinction event, and how it could teach us about potential future ocean extinctions. Plus we ask another marine expert to choose our Critter of the Month...

In this episode


01:21 - Antarctic species suffering from climate change

Researchers at the British Antarctic Survey have found an increase in iceberg scouring of the seafloor around the West Antarctic Peninsula, and that the chance of bryozoan colonies living...

Antarctic species suffering from climate change

David Barnes and his colleagues at the British Antarctic Survey have found that the sea-floor ecosystem of an area of the West Antarctic Peninsula is suffering from theeffects of climate change. The team were studying tiny organisms called bryozoansthat live on the sea floor, as a marker of the ecosystem's response to scouring byicebergs.

They also studied the duration of the skin of 'fast ice' that forms on thesea surface every winter. This skin helps to protect the shallower waters from beingscoured by ice flows, so if there is less ice in a particular year due to increasedtemperatures, then scouring of the seafloor communities will increase. They foundthat over the last 25 years, the duration of the fast ice has decreased, with now five days fewer ice coverage. Iceberg

There was also worrying data from looking at the bryozoans. Since 1997, the chance of a bryozoan colony reaching sexual maturity, around 2 years old, has halved. Obviously if they are killed before they can breed, this will have a damaging effect on the species. Plus benthic species like the bryozoans are important for carbon sequestration. Reduced sea ice coverage can mean an increase in growth, but the authors suggest that this will be counteracted by the damaging effects of ice scouring.

Prickly dogfish

03:16 - How sharks see in the deep sea

A discovery announced at the World Conference on Marine Biodiveristy reveals how deep sea sharks evolved eyesight to cope with the challenges of life in the dark depths.

How sharks see in the deep sea

Amy Newman from the University of Western Australia has discovered that the eyesight of deep sea sharks has evolved a variety of adaptations for finding food and avoiding getting eaten in the particular depths that they inhabit.

Prickly dogfishPresenting her work at the recent World Conference on Marine Biodiversity, Newman studied the light detecting cells, known as photoreceptors, in 7 species of deep water sharks all caught as incidentally as by-catch in trawling boats off the NW coast of New Zealand, from waters between 750 and 1100 m beneath the waves.

By examining the patterns of light receptors across the retina she found out a lot about how these sharks go about their daily lives, all that way down beneath the waves.

For example, she looked at the eyes of a very rare shark, the Beige catshark, which has only been found once before, which as well as another rare species, the McMillan's Catshark have a cluster of light detecting cells in a spot on their retina that allows them to catch sight of animals sneaking up on them from behind - and being fairly small sharks, around 50cm, it suggests that being able to spot a larger predatory shark approaching would be an excellent survival strategy.

Newman also found that all the species she looked at had a cluster of light detecting cells arranged to see clearly in the visual field right ahead of the shark - which would let them detect bioluminescent prey animals that they're prowling after.

The interesting thing about this research is how it's using detailed anatomical studies of dead specimens brought back up from the depths to understand more about the lives of animals that are otherwise extremely difficult to study in the wild as they roam around in the dark, deep seas.

Find out more:

World Conference on Marine Biodiversity

Moon jellyfish, Gijón Aquarium. Photograph by Julio Arrontes.

05:20 - Jellywatch shows a rise of slime

Initial results from the Jellywatch scheme set up in the Mediterranean Sea in 2008 suggest an increase in jellyfish blooms over the last few years.

Jellywatch shows a rise of slime

Another presentation at the World Conference on Marine Biodiversity in Aberdeen came from Professor Ferdinando Boero from the University of Salento in Italy. He launched a project with the Mediterranean Science Commission in 2008 called Jellywatch to get the public in Italy to monitor jellyfish blooms in the Mediterranean.

JellyfishThey produced posters to help people identify the jellies - aimed attourists, divers and fishermen. The project then expanded to Israel and Spain andother areas of the Mediterranean sea. The idea is to see what species make up these blooms - aggregations of large numbers of jellyfish, where and how frequently they occur.

They are a major problem for tourist areas, preventing people from going into the water, but also represent a more worrying trend - sometimes known as 'the rise of slime', with a shift in the balance of ecological 'power' in the Med. Due to habitat loss, pollution and particularly overfishing, many species of fish are under threat and are dwindling in number. The jellyfish then muscle in and fill the ecological niches left bare, creating what Professor Boero terms a 'gelatinous sea'.

Results from the early stages of the project suggest a marked increase in blooms in the last few years, plus a shift in the ranges of some jellies and even the influx of new species previously only found in the Atlantic. As the project is rolled out to other areas of the Med, the teams behind it hope that it will help us to understand the causes behind the increase in these jellyfish blooms.

Red Mangrove

07:41 - Plans underway for the 'IPCC for nature'

Plan for an Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) will do for nature what the IPCC does for climate change.

Plans underway for the 'IPCC for nature'

The latest news on an important new initiative in global conservation was  announced at the World conference on Marine Biodiversity with plans now well underway for the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) - which will do for nature what the IPCC does for climate change, and is being seen as a global response to tackle the demise of the natural world.

Because, while there are lots of organisations that work on issues biodiversity loss and the vital services that ecosystems provide us - things like pollinating crops, mitigating against floods, and providing food - but until now there hasn't been a joined up, global strategy to bring together all the expert information we have and use it to help make decisions about how best to protect the natural world - including the oceans, of course.Red Mangrove

There was a resolution from the United Nation General Assembly last December, and this month a plenary meeting in Nairobi in Kenya will see various groups get together to talk about how the IPBES will be set up and what it's programme of work will be.

Things we should be seeing coming out of the panel include regular expert assessments of the state of biodiversity around the world - similar to the 5-yearly assessment of climate change produced by the IPCC. The panel will also help identify and prioritise key areas where more science is needed, and provide support and capacity to help build bridges between scientists and decision makers.

It's an exciting development and something no-doubt we'll be hearing about much more about as the IPBES gets up and running.

Find out more:


Dickinsonia fossil

11:02 - Ediacaran and Burgess Shale fossils

Complex life forms first evolved in the oceans around 630 million years ago, but they didn't look much like to anything we see today...

Ediacaran and Burgess Shale fossils
with Ken McNamara, Sedgwick Museum of Earth Sciences, Cambridge

Life on Earth evolved in the oceans around 4 billion years ago, but it's not life that we could see with the naked eye. The first complex life we see in the fossil record turns up around 630 million years ago, but they still don't bear much resemblance to anything we see today. Sarah spoke to Ken McNamara of the Sedgwick Museum in Cambridge, to find out more about the evolutionary experiments of the Ediacaran and Cambrian eras... 

A fossilised stromatolite:

Fossil stromatolite Sedgwick Museum


Dickinsonia, an example of the bizarre Ediacaran biota:

Dickinsonia fossil


A reconstruction of the Burgess Shale fossil Wiwaxia:

Wiwaxia reconstruction Sedgwick Museum 2

Ken - This rather unprepossessing lump of rock doesn't looking very exciting at all, but in terms of what it actually is, is the earliest evidence of life on earth. So it's a lump of rock that's about 3.5 billion years old and the strange structures are actually made by the activity of microbial communities. You've got the same sort of organisms today - cyanobacteria, that we call blue-green algae - making these same sort of structures in lakes and shallow seas today. They were doing it 3.5 billion years ago. And really that's the only evidence of life in the oceans for a phenomenal period of time - for about 3 billion years.

Then, at some stage, we had the evolution of more complex cells of which animals and plants are make - eukaryotic cells. But it wasn't until you're getting much closer to the modern day, 6, 7, 800 million years ago that you had these cells coming together producing multicellular, more complex organisms.

Sarah - So these other fossils that I can see here on the table, are they the first evidence of complex, multicellular life?

Ken - They are. You find evidence there are trace fossils, trails of who knows what made them, worm-like things. Seemingly relatively quickly just under 600 million years ago you start finding really quite large fossils, and complex-looking fossils. This fauna that's known as the Ediacaran, well I shouldn't say fauna, Ediacaran biota, are either round jellyfish-type things or they're more frond-like structures. You can break them down into these two groups.

They have a resemblance to later forms but there's something not quite right about them. I like to call them the gutless wonders, because you can't see any sign of a mouth, any sign of an anus, no sign of a gut. So there's this big problem: what were these things? Where they animals? If so, how did they get their nutrients? How did they feed? So the big question is, are they the ancestors of all alter animals, or are they something completely different. And that's one of the suggestions that have been put forward a couple of times. Maybe they were a great evolutionary experiment?

Sarah - So these were pre-Cambrian. I think a lot of people will have heard of the Cambrian explosion of life where we saw this massive explosion of all different types of body forms, of complex organisms. These are earlier than that?

Ken - Yes they are. They immediately pre-date the Cambrian explosion. Then you had this amazing change around about 540 million years there's a relatively sudden change in the nature of fossils. At this time there were probably sponges and things around but at the beginning of the Cambrian there was the relatively rapid appearance of whole groups of organisms that we're familiar with today, like clams, worms, even very primitive early fish, early vertebrates. Much more familiar-looking organisms that had recognisable mouths, they had guts that we even have the gut contents from some of them, we know what they fed on. And so we can see that they developed this ability to feed off plants, but also to feed off other animals. So it's a completely different change in lifestyle.

Sarah - And I believe you have some examples here in the museum of probably the most famous examples of the Cambrian explosion which are from the Burgess Shale in Canada.

Ken - Yes, we have some really good specimens here in the Sedgwick Museum because this is where a lot of the original research was done in the last 30 years. So we can go and have a look at some of those if you like.

Sarah - So what are we looking at here then?

Ken - What characterises the Burgess Shale is their soft parts are preserved. Not only that but in rocks of this age we start finding animals develop the ability to produce minerals - hard shells or spines - which is something that the Ediacaran animals just didn't do. The advantage of this is there's a greater chance of it being fossilised. But surprisingly there are a lot of deposits of this age where you have the soft tissue preserved. So we can learn a lot about the whole biology of the animals.

One that I really like is this strange slug, worm like thing here. It's called Wiwaxia and it has what looks like a whole row of steak knives sticking out of its back. You would look at them and say it's got those because they are protective. If something tried to eat it, it would get a mouthful of those spines. It wouldn't taste very nice. It's also got armoured plates.

This is what characterises what was going on the Cambrian explosion. We seem to have the evolution of predators and prey. Animals develop this ability to feed on other animals and this is what basically drives a lot of evolution: predation pressure. And so the predators are trying to outcompete the prey and the prey are coming up with new strategies to stop being eaten. So Wiwaxia probably did it really quite successfully for a while.

There's another thing here called Halceria, which is like a huge slug but it's covered in amazing armour. It's like medieval armour of tiny, really hard plates. But we also have animals that are quite similar to modern day things. We have crustaceans there that really look quite like modern day crustaceans. We have a reconstruction that we've done of one of these. So there are some groups of organisms that evolved at this time, that hit on the right body form and haven't changed dramatically over a long period of time. Their interspersed with some of these weird things like Wiwaxia, with steak knives, that last for a short period of time and then became extinct.

We know there were predators around because we have examples of these and the most spectacular is this amazing thing called Anomolocaris, which is a sort of arthropod, so it's sort of related to lobsters and crabs and so on, and they grew up to nearly a metre long. Huge claw-like structures at the front and an amazing mouth part. And one finds lots of other fossils of things like trilobites, segments animals that are now extinct, but with a big armoured head, and many of these you find with bits broken off them, bite marks, and they've survived and they've re-grown part of the bite mark.

So there was a lot of predation going on. Sometimes it was successful, sometimes it wasn't successful. So as I said, this predation pressure which is driving a lot of evolution, and that's what really marks the beginning of the Cambrian explosion, and that's then continued on to the present day.

Sarah - So this is the first real example of things that we might recognise today but also some pretty wacky stuff as well, that perhaps wasn't as successful. It's really an example of evolution in action - things that have been successful and things that haven't?

Ken - That's right. It's really what you'd expect. Early on you'd have these evolutionary experiments, some will work, some won't. There's another one that's not shown here called Opabinia, which is a bizarre animals that had 5 huge eyes on its head, and this long thing coming out the front that looked like a vacuum cleaner. So there were some really quite bizarre experiments that didn't work. But a lot of standard ones that did and so we have these crustacean-like animals that are quite similar to things that are around today.

Sarah - and I believe also some things that are perhaps related very distantly to ourselves, as well?

Ken - Indeed. It's become realised in relatively recent times both in this deposit but also in other similar deposits, there's one in China, slightly older, called the Chengjiang fauna, there are worm-like animals but they have distinctive structures in them, particularly a notochord, precursor of a neural spine, that do indicate that chordates, that vertebrates - part of - were around at this time. So these were the earliest ancestral type fish, which evolved into amphibians, reptiles and us. So our long-lost ancestors were lurking around in these muds in Cambrian times.



20:17 - Exploring the oceans' greatest catastrophe

Why did 90% of ocean life vanish 250 million years ago? We find out as we dive into Permian seas to investigate an ocean in crisis.

Exploring the oceans' greatest catastrophe
with Paul Wignall, Leeds University

Helen - There have been 5 so-called Mass extinctions in the history of the planet earth when large swathes of life on land and in the sea disappeared. Most famous of these events was the one 65 million years ago that saw the end of the dinosaurs, probably thanks to a massive meteor crashing into the earth.

But the most devastating extinction took place in the oceans long before dinosaurs evolved, back at the end of the Permian era, around 250 million years ago.

Paul Wignall from Leeds University, here in the UK, is a geologist who researches the Permian extinction and I chatted to him about just want went on back then.

Paul - In a nutshell every died basically. To a first order you're seeing the extinction of just about everything. About 95% of species on the level seafloor disappeared. Most fish groups disappeared as well. So, it was pretty devastating.

It's so big is this extinction that we almost take the world back to the pre-Cambrian, the time before complex life evolved. So we have in the seas of the earliest Triassic, after the extinction, were in a sense almost dead seas, there's not much around. We just have a lot of microbial life which is very much like the pre-Cambrian world.

Helen - And what were the groups that we just don't see any more? Which ones were snapped out and wiped out completely?

TrilobitePaul - The end of the Permian, the groups that we loose completely, there's 2 major groups of corals, and they disappear. And although we have corals today they're not actually very closely related to these Permian corals. The trilobites, famous fossils, die out at this event. And things called sea scorpions, they go out at this time as well.

Helen - They were really big weren't they?

Paul - They were. They'd managed to colonise rivers and freshwater environments by the late Permian as well. They don't cross the boundary, so we don't see those ever again.

The main shelly group at this time was a group known as the brachiopods, which Spirifurella & Muirwoodiaswe do actually have today, I think you can find them around the shores of New Zealand in particular, but in the Permian they were the most common fossil around. So they were almost entirely wiped out.

Helen - And in terms of large vertebrate life in the oceans, was there much going on at the time in the Permian.

Paul - Various fish groups, particularly some armoured fish, with heavy armoured scales, they disappear. A lot of the famous marine reptiles like ichthyosaurs and plesiosaurs, they actually come along after the extinction. So following the extinction event we actually see a lot of reptile groups return to the oceans and you get all sorts of swimming reptiles in the Triassic, so in a way they benefit from the extinction because they radiate afterwards.

Helen - Life on land also took an enormous knock didn't it? What was going on there at the time as well?

Paul - The end Permian extinction was utterly catastrophic on land. We see the loss of all forests at this time, all major trees and things die off. It's also the real extinction event for insects, because insects as we know are a very successful group which are generally diversifying all the time, but that wasn't the case at the end of the Permian, so we loose a lot of insect groups. Something severe happened on land and in the sea around the same time. We're looking at a whole global ecosystem breakdown.

Helen - So, the Permian extinction really did shake up life on earth like never before, and the big question is - why did it happen? What was it that made so many species go extinct?

Over the years, various theories have been drawn up - some say it could have been another meteorite impact like the one that wiped out the dinosaurs, although there isn't too much evidence for that.

But as Paul explained, there was something rather spectacular going on at the time that could ultimately be to blame.

Paul - We've got the culprit. There's a huge amount of volcanism going on at that Siberian trapp volcano depictiontime in Siberia so that seems to be the giant smoking gun, so we're trying to link that volcanism in to that extinction in the oceans.

Helen - And this was enormous volcanism wasn't it? We can't actually picture in our minds compared to the kind of volcanic activity we see today. It was enormous wasn't it?

Paul - Yes it was. It's a style of volcanism which fortunately we don't see today but it's known as flood basalt volcanism and basically it involves enormous eruptions involving thousands of cubic kms of lava. Most volcanic eruptions today involve less than a cubic km of lava. So we're talking about enormous individual flows covering large areas of Siberia.

But with those flows a lot of volcanic gas would come out as well.

Helen - And it was that potent cocktail of volcanic gases that's thought to have triggered the crisis in the Permian oceans.

One of the gases spewed out by the Siberian traps, those gigantic volcanoes, was sulphur dioxide - which has various effects in the atmosphere including forming acid rain.

And there was also an awful lot of carbon dioxide released, which as we know from what us humans have been getting up to in recent times is a powerful greenhouse gas, and there's evidence that back in the Permian the earth warmed up and its thought this led to the oceans becoming very low in oxygen, making them distinctly inhospitable for most forms of life:

Paul - If you look at the oceans today they're extremely well ventilated - there's oxygen available everywhere in the world's oceans and that's because they circulate very effectively. The circulation is essentially driven by the temperature difference between the poles and low latitudes, the equator, so you generate cold, dense water at the poles, which sinks and then warms surface waters travels to the poles, like the Gulf Stream for example.

Back in the Permian presumably a similar sort of circulation was going on but then if you turn that off that ocean conveyor as it's know, they you'd cease to supply so much oxygen to the ocean waters.

It's a bit like on a giant scale if you stick a goldfish bowl on a window on a sunny day that goldfish bowl will warm up and the oxygen in the water will decline and your goldfish will probably die.

EumorphotisSarah - Ok, so Helen we've got carbon dioxide billowing out of these enormous volcanoes and that would have heated up the planet and turned the oceans stagnant - which already makes conditions pretty unbearable- but what about the other affects of CO2? Did the oceans become more acidic as well, back then as they seem to be doing now?

Helen - Well, it's interesting because the idea of ocean acidification has only really been on our radar for less than a decade, and it's the scientists studying our present-day oceans and atmosphere who came up with the theory, and found that over the past 200 years the oceans have become around 30% more acidic, a consequence, we think, of more and more carbon dioxide dissolving into the oceans from the atmosphere - because as well as being a greenhouse gas, carbon dioxide is acidic.

But it was this discovery of recent ocean acidification - and concerns about what could happen in the future - that gave geologists studying the past, the idea that maybe this was what happened then too.

Paul - It's actually very hard thing to test for back in the rock record because acidification essentially dissolves things of course, it dissolves shells and it dissolves limestones and things. So in effect by removing something it leaves no evidence behind.

You can do more indirect ways of looking for it, for example you can look to see if the extinction was selective. Was it particularly hard on organisms whose shells dissolve easily? And that sort of work is really only just being done so we don't yet know the answer to that.

Helen - There was one study out earlier this year that provides some evidence of acidification in Permian seas, from a team who looked at Calcium isotopes in limestone deposits in China. But as Paul said, we're still a way off knowing if that's really what happened and what impact it had.

Sarah - So, we had this massive extinction, 250 million years ago, that virtually wiped out life in the oceans - but can this tell us anything about changes taking place with oceanlife today and the prospects for the future?

Helen - Well, it's often said that we are entering the 6th mass extinction, and this one hasn't got anything to do with asteroids or volcanoes but it's us humans who are to blame for churning out pollutants and greenhouse gases, and for wiping out habitats and species around the world.

The Permian extinction was far more catastrophic than even the gloomiest predictions for the impacts of humans on the planet, and it happened over a much longer time frame - tens of thousands of years - compared to the impacts we're having over a matter of decades.

But even so, there are some aspects of the Permian extinction that may help us understand what's going on today, and what might lie in store.

Acidification studies are one area that will surely benefit from understanding what happened in the past and how different animals responded to it, and as Paul said, that's ongoing research.

And studies of what happened following the Permian extinction tell us is how quickly surviving species were able to diversity and restore global biodiversity to its former glory. And that shows us how different groups of animals evolve into new species at different rates:

Paul - Things like bivalves are like evolutionary carthorses, they just plod along, they'll take a long time to recover. Other groups like for example fish, they evolve quickly, so we can predict that they'll start diversifying again very quickly if we drive them to extinction.

But I'm talking as a geologist here, so when I say something evolves quickly I'll say fish probably will have recovered in a million/1.5million years, bivalves might take 15-20 millions years. We're talking about long time scales. But it's quite easy to predict what will bounce back quicker than say other groups.

Helen - But I suppose that's a geologist's point of view on the planet and we may or may not be around to see this?

Paul - As a measure of just how long it takes, the end Permian extinction took about 80-100 million years later you've finally got back to the pre-extinction diversity levels, so it is a long time. Life gets there eventually, but anything as big as the end Permian extinction takes a long time to recover from.

Helen - It was thought that reefs took 5 million years to recover after the Permian extinction, but a new study just out in the journal Nature Geoscience shows that in fact it only took 1.5 million years for reefs to reform with multicellular life like sponges and serpulid worms, showing that as soon as environmental conditions returned to normal, reefs started growing again.

But as Paul said, it takes a very long time for life to recover from a mass extinction, and while, in the grand scheme of life on earth, things will go probably on, from our human perspective we can't simply expect to sit by and watch life recover from the damage we are inflicting on the oceans today- so efforts to protect life in the ocean are really very important indeed.

Find out more:

Paul Wignall, Leeds University

The Permo-Triassic Extinction - information from the Palaeobiology and Biodiversity Research Group at the University of Bristol

Sea cucumber snuggle - Scuba diving on the Great Barrier Reef off the coast of Australia

31:10 - Critter of the Month - Holothurians

Kevin Hardy tells us which marine creature he'd like to be and why...

Critter of the Month - Holothurians
with Kevin Hardy, SCRIPPS Institution of Oceanography

Kevin Hardy tells us which marine creature he'd like to be and why...

Sea Cucumber

I'm Kevin Hardy from the Scripps Institution of Oceanography. If I could be a marine critter I would be a holothurian.

I think that's a great sounding name to begin with, but they're also cool little animals. They run around and they have different forms. Some look like flat fish, some look like caterpillars, some can swim through the water column, they look like nudibranchs. You see them occasionally solo walking around by themselves, other times they're in herds. So, I just think they're cool.

What's exciting about them is I think their behaviour: they seem very placid, very calm. Totally unlike I am. They seem to get along with each other pretty fine, they come in brilliant colours. We see them off the Sea of Cortez, we see them offshore, pretty much anywhere you go and certainly in the deep ocean, in trenches, their down there.


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