0:00:05 > 0:00:09Every day, when the tide retreats, a secret world is exposed.
0:00:09 > 0:00:12A magical and intriguing place,
0:00:12 > 0:00:15full of remarkable and unusual characters.
0:00:15 > 0:00:17SEAGULLS CALL
0:00:17 > 0:00:20The rock pool is a cornucopia of life.
0:00:20 > 0:00:23It's full of diverse animals.
0:00:23 > 0:00:25Some we're familiar with, some we're not.
0:00:25 > 0:00:29But this unique environment experiences some of the most
0:00:29 > 0:00:32extreme conditions in the natural world.
0:00:34 > 0:00:36My name's Professor Richard Fortey.
0:00:36 > 0:00:39I just love rootling around in rock pools.
0:00:39 > 0:00:43But I'm a palaeontologist, so for me, rock pools are more than
0:00:43 > 0:00:46just a collection of wonderful and interesting animals.
0:00:46 > 0:00:49They also provide a window into the past.
0:00:51 > 0:00:53Part the weeds on any rock pool
0:00:53 > 0:00:57and you open the curtains onto a life and death drama
0:00:57 > 0:01:00that has been played out for hundreds of millions of years.
0:01:02 > 0:01:05Some of the creatures that live here have outlived the dinosaurs,
0:01:05 > 0:01:09and have evolved truly extraordinary adaptations to survive.
0:01:12 > 0:01:15I want to show you how rock pool creatures have stood
0:01:15 > 0:01:17the test of time.
0:01:29 > 0:01:31This is the intertidal zone -
0:01:31 > 0:01:35the land between the high and low tide marks.
0:01:35 > 0:01:40Here, animals have to cope with extreme fluctuations in moisture,
0:01:40 > 0:01:45temperature and salinity, as well as predators on land and in sea.
0:01:45 > 0:01:49It is a hostile place in which to survive.
0:01:53 > 0:01:57As the tide changes, so do conditions on the beach,
0:01:57 > 0:02:01and this has a profound effect on all living things,
0:02:01 > 0:02:03even the sea weeds.
0:02:03 > 0:02:05For more than a billion years,
0:02:05 > 0:02:11life on Earth was dominated by very simple single-celled organisms.
0:02:11 > 0:02:12Slime, if you like.
0:02:12 > 0:02:14This rock's covered in it.
0:02:14 > 0:02:19But those organisms included photosynthesising blue-green
0:02:19 > 0:02:24bacteria called cyanobacteria that formed living films and breathed
0:02:24 > 0:02:30oxygen into the atmosphere, thereby transforming the early Earth.
0:02:30 > 0:02:34And about 1.3 billion years ago, they were joined by much larger
0:02:34 > 0:02:37multi-celled organisms - algae.
0:02:37 > 0:02:40Doing the same job, still photosynthetic,
0:02:40 > 0:02:45but these today dominate what we see on the beach and in the rock pools.
0:02:45 > 0:02:48Of course, most people know it simply as seaweed.
0:02:52 > 0:02:56With more than 9,000 species of seaweed in the UK alone,
0:02:56 > 0:03:01the sheer variety and volume of them is staggering.
0:03:01 > 0:03:06A quarter of the total global energy captured by photosynthesis is
0:03:06 > 0:03:08fixed here in the intertidal zone.
0:03:08 > 0:03:14So seaweeds are the basis of a rich and complex food chain.
0:03:16 > 0:03:20Constantly changing salinity and exposure can have a dramatic effect
0:03:20 > 0:03:24on their survival, and determine where they colonise the beach.
0:03:26 > 0:03:29Distinct patterns from upper to lower shore can be seen.
0:03:29 > 0:03:32This is known as zonation.
0:03:32 > 0:03:37The intertidal zone can be divided into four vertical zones...
0:03:45 > 0:03:49Each zone is exposed to moisture, temperature and salinity
0:03:49 > 0:03:53in different ways, and this dictates what can survive.
0:03:54 > 0:03:57Seaweed produce eggs and sperm.
0:03:57 > 0:04:01After 24 hours, the fertilised eggs develop into embryos
0:04:01 > 0:04:06which are extremely sensitive to the fluctuating levels of salinity
0:04:06 > 0:04:08in each zone.
0:04:10 > 0:04:14Exposure to rainwater can have a dramatic effect.
0:04:17 > 0:04:18It's dead.
0:04:21 > 0:04:24The rainwater penetrates the cells by osmosis,
0:04:24 > 0:04:27causing them to swell and burst.
0:04:30 > 0:04:34And this is what determines where different species of seaweed
0:04:34 > 0:04:36colonise the beach.
0:04:36 > 0:04:39The environments in the different intertidal zones play
0:04:39 > 0:04:43a vital role in controlling where an organism can survive.
0:04:48 > 0:04:51Rock pool animals can go without food for a long time,
0:04:51 > 0:04:56they can survive changes in salinity, they're extremely tough.
0:04:56 > 0:05:00All this means they've evolved a whole series of adaptations
0:05:00 > 0:05:03to cope with life in the in-between zone.
0:05:05 > 0:05:11As the tide falls, life becomes very different for the creatures here.
0:05:11 > 0:05:16The exposed shore is now subject to unpredictable changes.
0:05:16 > 0:05:18Changes that depend on the weather,
0:05:18 > 0:05:22the time of year, and the time of day.
0:05:22 > 0:05:26Here, temperatures can range from freezing to baking,
0:05:26 > 0:05:28oxygen levels fluctuate,
0:05:28 > 0:05:31and salinity can increase or decrease,
0:05:31 > 0:05:35causing body tissues to dehydrate or swell with water.
0:05:35 > 0:05:40But before any of these changes even begin to come into play,
0:05:40 > 0:05:42there is a more immediate problem.
0:05:44 > 0:05:47There is now less room for everyone to live
0:05:47 > 0:05:49and resources are diminished.
0:05:51 > 0:05:54Everything is dictated by competition.
0:05:54 > 0:05:58Finding a good position becomes a matter of life or death
0:05:58 > 0:05:59for all the creatures here.
0:06:01 > 0:06:04For anemones, it is important to have a good spot
0:06:04 > 0:06:06to catch the most food.
0:06:07 > 0:06:11Anemones appear sedentary, but they do move around very slowly.
0:06:14 > 0:06:19To find, secure and defend the best spot, they have a secret weapon.
0:06:21 > 0:06:23'And to shed some light on their lives,
0:06:23 > 0:06:27'Dr Mark Briffa of the University of Plymouth has come into the lab.'
0:06:28 > 0:06:33So, Mark, sea anemones are beautiful creatures,
0:06:33 > 0:06:36but most people might think that they're pretty inactive,
0:06:36 > 0:06:39they just sit there waiting for food to come along.
0:06:39 > 0:06:44Yes, they are relatively slow-moving animals, but they are animals
0:06:44 > 0:06:46and that means that they have to consume food,
0:06:46 > 0:06:49and one of the things that sea anemones have to do
0:06:49 > 0:06:52before they can consume it is to capture their food.
0:06:52 > 0:06:55Can you see the feeding tentacles?
0:06:55 > 0:06:59There are six rows of tentacles on the top of the animal, 192 in total,
0:06:59 > 0:07:02and just by looking at them for a small amount of time,
0:07:02 > 0:07:05you can see that the tentacles are moving about,
0:07:05 > 0:07:09and these tentacles are there to trap food and bring it in
0:07:09 > 0:07:12towards this structure in the middle of the animal.
0:07:12 > 0:07:13This is the oral disc.
0:07:13 > 0:07:15- Otherwise known as a mouth. - A mouth, yeah.
0:07:16 > 0:07:18'Nematocysts are stinging cells
0:07:18 > 0:07:20'common to all anemones and jellyfish.'
0:07:22 > 0:07:25'When stimulated, they fire a venomous dart
0:07:25 > 0:07:27'attached to a thread into their prey.'
0:07:29 > 0:07:32We can look at the use of the tentacles to trap food
0:07:32 > 0:07:37by taking a small piece of food - this is a little piece of limpet -
0:07:37 > 0:07:41and dropping it over the ring of tentacles.
0:07:41 > 0:07:44They kind of close in on it and pull it down.
0:07:44 > 0:07:46Oh, it likes that. It likes that a lot.
0:07:46 > 0:07:48It's closing all six rings,
0:07:48 > 0:07:52it's pushed the food back down towards its mouth.
0:07:52 > 0:07:54And they're not just for trapping prey, either.
0:07:54 > 0:07:56In this species of sea anemone,
0:07:56 > 0:08:00there are specialised tentacles simply for fighting...
0:08:01 > 0:08:06..and these specialised tentacles appear as little blue beadlets
0:08:06 > 0:08:11in a ring around the outside of the six rings of the feeding tentacles,
0:08:11 > 0:08:14and they will use them in combat with rival anemones
0:08:14 > 0:08:20of the same species, and therefore require exactly the same resources
0:08:20 > 0:08:22in terms of a good place in the rock pool.
0:08:25 > 0:08:28'Using a specialist time-lapse camera,
0:08:28 > 0:08:31'we can speed these battles up to see what's really happening.'
0:08:33 > 0:08:37'Twisting their flexible bodies, anemones take aggressive swipes
0:08:37 > 0:08:40'at each other, tearing off ribbons of skin.'
0:08:44 > 0:08:48'Losers have no choice but to find another place to settle.'
0:08:58 > 0:09:02'We may barely give anemones a second glance,
0:09:02 > 0:09:05'but their remarkable fighting behaviour has allowed them
0:09:05 > 0:09:08'to colonise the most sought-after locations in the rock pool,
0:09:08 > 0:09:11'and has helped them thrive on our beaches
0:09:11 > 0:09:14'for around 540 million years.'
0:09:16 > 0:09:20'Other creatures have dealt with the lack of space very differently.'
0:09:20 > 0:09:24'They have left the pools altogether, taking up residence
0:09:24 > 0:09:27'on the rocks where they are exposed at low tide.'
0:09:29 > 0:09:34'Around 530 million years ago, molluscs developed hard shells
0:09:34 > 0:09:37'to house their soft body parts,
0:09:37 > 0:09:41'creating a microclimate into which they could retreat.'
0:09:41 > 0:09:44And one of the first animals to do this is still with us.
0:09:44 > 0:09:47It's a living fossil. The chiton.
0:09:48 > 0:09:52The chiton has a number of plates which allow it to shuffle around
0:09:52 > 0:09:55and grip tightly to the surface of the rock.
0:09:55 > 0:09:59But an even more effective way of doing this is under a single shell,
0:09:59 > 0:10:02and the mollusc that has done this most successfully
0:10:02 > 0:10:05is still with us in every rock pool and on every rocky shore.
0:10:05 > 0:10:06It's the limpet.
0:10:09 > 0:10:13'Professor Stephen Hawkins of the University of Southampton
0:10:13 > 0:10:14'is a limpet expert.'
0:10:16 > 0:10:18I'm told that they vary in conicality
0:10:18 > 0:10:20according to where they are on the shore.
0:10:20 > 0:10:23Yes, and also with age.
0:10:23 > 0:10:27I think as they get bigger and older, they tend to get more conical,
0:10:27 > 0:10:29and it makes quite a lot of sense to be conical like this,
0:10:29 > 0:10:34because the circumference is where water gets lost when the tide's out.
0:10:37 > 0:10:40'Retaining moisture is vital if the limpet is to survive
0:10:40 > 0:10:42'the drying effects of the sun.'
0:10:46 > 0:10:51They've got a big extensive foot, you can see on this animal here,
0:10:51 > 0:10:53and essentially, it's a very complicated
0:10:53 > 0:10:56biological suction device. That's how it works.
0:10:57 > 0:11:00'This adaptation allows them to hold on to the rock
0:11:00 > 0:11:02'and resist the force of the waves.'
0:11:04 > 0:11:07'Surprisingly, limpets are territorial.
0:11:07 > 0:11:10'They create a depression in the rock known as a home scar.'
0:11:11 > 0:11:13'As the tide starts to go down
0:11:13 > 0:11:16'they return to this place and hunker securely down.'
0:11:21 > 0:11:25'Territorial fights are common, and losers are prised off the rock.'
0:11:28 > 0:11:29'As the tide covers them,
0:11:29 > 0:11:32'limpets leave their home scars and begin to feed.'
0:11:34 > 0:11:37'Limpets are very important grazers on the seashore.
0:11:37 > 0:11:40'However, there is intense competition.'
0:11:41 > 0:11:43'To see exactly what impact this has,
0:11:43 > 0:11:46'we have to go to the laboratory.'
0:11:46 > 0:11:48I collected these this morning at low tide
0:11:48 > 0:11:50just as the tide was about to come over them,
0:11:50 > 0:11:54so we should be able to stimulate them to set off on
0:11:54 > 0:11:57their foraging excursions to go off feeding, if we put them in the tank.
0:12:05 > 0:12:09It doesn't take long before they sense they're surrounded with water.
0:12:09 > 0:12:12Little tentacles coming out?
0:12:12 > 0:12:14Yes, they have these fantastic sensory tentacles
0:12:14 > 0:12:16all the way round the edge of the shell.
0:12:16 > 0:12:20The big ones, the primary tentacles, actually match with those rays
0:12:20 > 0:12:23you can see on the shell, and there's smaller tentacles
0:12:23 > 0:12:27in between, and that gives lots of information about the physical
0:12:27 > 0:12:30and biological environment when they're out foraging.
0:12:30 > 0:12:34And foraging means scraping algae and other things
0:12:34 > 0:12:35off the surface of the rock.
0:12:35 > 0:12:38That's right. They feed by scraping the rock surface
0:12:38 > 0:12:39using their radula, yes.
0:12:41 > 0:12:44'The radula of the limpet is a ribbon-like tongue
0:12:44 > 0:12:45'covered in teeth.
0:12:46 > 0:12:49'It moves back and forth, scraping algal slime from the rocks.'
0:12:51 > 0:12:53'The limpet's radula is tipped with haematite,
0:12:53 > 0:12:56'an extremely hard material that allows the limpets
0:12:56 > 0:12:58'to graze on hard surfaces.'
0:13:00 > 0:13:03Stephen's research has shown that limpets have a profound effect
0:13:03 > 0:13:05on the ecology of the seashore.
0:13:05 > 0:13:09When they're off foraging, and this is where I fenced the rock
0:13:09 > 0:13:10to keep limpets out,
0:13:10 > 0:13:13and all the rest of the area here is where limpets were able
0:13:13 > 0:13:15to forage freely, and just six months later...
0:13:15 > 0:13:16Wow.
0:13:16 > 0:13:17Yes, it's amazing, isn't it?
0:13:17 > 0:13:21Six months later there's a really dense growth of seaweeds,
0:13:21 > 0:13:25bladder wrack, fucoids, covering the rock in the absence
0:13:25 > 0:13:27of the limpet grazing, so basically,
0:13:27 > 0:13:30the limpets, through their radulae, really control the algae.
0:13:32 > 0:13:36'So although limpets appear to be immobile and stuck to the rocks,
0:13:36 > 0:13:40'in fact, they have a much more complicated life cycle
0:13:40 > 0:13:44'that plays an important part in the ecology of the intertidal zone.'
0:13:49 > 0:13:54'The rising tide gives animals an opportunity to hunt for food,
0:13:54 > 0:13:56'but this also means they can become the hunted.'
0:14:00 > 0:14:04'Starfish belong to a phylum of animals called the echinoderms,
0:14:04 > 0:14:05'which first appeared in the fossil record
0:14:05 > 0:14:07'more than 500 million years ago.'
0:14:08 > 0:14:11'Starfish have macabre eating habits.
0:14:13 > 0:14:15'Using their strong sticky tube feet,
0:14:15 > 0:14:19'they force open the shells of molluscs and then,
0:14:19 > 0:14:21'pushing their stomach out through their mouth,
0:14:21 > 0:14:23'they digest the animal inside.'
0:14:31 > 0:14:35'Limpets have been locked in an arms race with starfish for millions
0:14:35 > 0:14:39'of years, and have evolved their own way of dealing with them.'
0:14:41 > 0:14:44So what are we looking for here?
0:14:44 > 0:14:48What happens, usually, is that the limpets get agitated
0:14:48 > 0:14:50when they sense a predator in the area and then,
0:14:50 > 0:14:53when the starfish is in contact with the limpet,
0:14:53 > 0:14:54the limpet tends to raise up
0:14:54 > 0:14:59and then it will often stamp down on the starfish and maybe drive it off.
0:15:05 > 0:15:06'In a rock pool,
0:15:06 > 0:15:10'there is nothing quite as sinister as a marauding starfish.'
0:15:22 > 0:15:25'Small limpets have no choice but to flee.'
0:15:28 > 0:15:30'A lucky escape.'
0:15:34 > 0:15:37'Large limpets, however, stand their ground.'
0:15:43 > 0:15:47'Using the edge of the shell, a limpet can push the starfish away
0:15:47 > 0:15:49'to prevent it climbing on top.'
0:15:49 > 0:15:51Look at that!
0:15:51 > 0:15:54'Continually scraping at the arm can damage the tube feet,
0:15:54 > 0:15:56'deterring an attack.'
0:15:58 > 0:16:01I don't think I'd like to be approached by a great battery
0:16:01 > 0:16:03of wiggly tube feet, if I was a limpet.
0:16:03 > 0:16:05There he goes. Look at that.
0:16:06 > 0:16:08It's really very agitated.
0:16:08 > 0:16:11Well, we can't say that rock pools lack drama.
0:16:17 > 0:16:18'Unseen by us,
0:16:18 > 0:16:21'there are many battles being fought beneath the waves.'
0:16:22 > 0:16:27'Over time, predators and prey have developed a range of adaptations
0:16:27 > 0:16:28'to attack and defend.'
0:16:29 > 0:16:32This is a dog whelk.
0:16:32 > 0:16:34A fearsome predator in the rock pools.
0:16:36 > 0:16:39'This carnivore has devised an ingenious way
0:16:39 > 0:16:41'of hunting other molluscs...
0:16:43 > 0:16:46'..and one of its favourite prey are mussels.'
0:16:50 > 0:16:53'Mussels are filter feeders sieving off the abundant food
0:16:53 > 0:16:54'that drifts in the upper ocean.'
0:16:57 > 0:17:00'They attach themselves to the rock surface by strong threads
0:17:00 > 0:17:03'which they secrete through their muscular foot.'
0:17:05 > 0:17:08'These threads enable them to cling to the rocks,
0:17:08 > 0:17:11'despite the relentless pounding of the ocean waves.'
0:17:13 > 0:17:16However, the stationary mussel
0:17:16 > 0:17:19is an easy target for prowling dog whelks.
0:17:21 > 0:17:24Their lethal weapon is a radula.
0:17:25 > 0:17:28A short, horny ribbon containing many rows of teeth,
0:17:28 > 0:17:32which are used like a file in combination with an acid secretion,
0:17:32 > 0:17:36to drill through the shells and tear the flesh of the mussel.
0:17:38 > 0:17:39It's a gruesome attack.
0:17:42 > 0:17:45Mussels, however, can turn the tables on a dog whelk.
0:17:46 > 0:17:49Sensing a nearby attack, others in the colony
0:17:49 > 0:17:51start to produce more and more sticky threads.
0:17:53 > 0:17:56If they make contact, it can spell doom for the dog whelk,
0:17:56 > 0:17:58which will starve to death.
0:18:03 > 0:18:07The hard shell of molluscs like the dog whelk
0:18:07 > 0:18:12persist long after the soft parts of the animal itself have decayed away,
0:18:13 > 0:18:15but these empty shells don't go to waste.
0:18:19 > 0:18:23In the rock pool, when one species dies or moves on,
0:18:23 > 0:18:24another takes over.
0:18:27 > 0:18:28Empty shells are put to good use
0:18:28 > 0:18:33by one of my favourite rock pool creatures - hermit crabs.
0:18:34 > 0:18:38Hermit crabs use shells as a very effective defence against predators,
0:18:38 > 0:18:42and their bodies have evolved to fit them perfectly.
0:18:43 > 0:18:46Unlike other crabs, their abdomen has become soft
0:18:46 > 0:18:49and asymmetrical, and their back legs are very reduced,
0:18:49 > 0:18:52allowing them to fit inside shells.
0:18:53 > 0:18:57The asymmetry of their claws also allows them to close up
0:18:57 > 0:19:00the entrance to the shell as a defence against predators.
0:19:03 > 0:19:07The crab's shell must not only be tough enough to withstand an attack,
0:19:07 > 0:19:09it must also afford it some camouflage.
0:19:11 > 0:19:14So these shells are obviously a protection.
0:19:14 > 0:19:15That's right.
0:19:15 > 0:19:17But are the crabs even choosier
0:19:17 > 0:19:20about which types of shells they pick up?
0:19:20 > 0:19:24The crabs are incredibly choosy about what they want.
0:19:24 > 0:19:27They'll spend a lot of time and effort deciding
0:19:27 > 0:19:31whether to change shells, whether a potential new shell is a good one.
0:19:31 > 0:19:36I mean, they're also known to be particular about the colour of the
0:19:36 > 0:19:42shell, at least in terms of if it's contrast against the background.
0:19:42 > 0:19:45We can run a little experiment here, so what I have are two containers
0:19:45 > 0:19:47with a dark coloured substrate,
0:19:47 > 0:19:52and I have some littorina obtusata shells.
0:19:52 > 0:19:55These are called citrina and dark reticulata.
0:19:55 > 0:19:59The only thing that's really different about them is the colour.
0:19:59 > 0:20:03What I'm going to do is place these shells, so you can see straight away
0:20:03 > 0:20:08that, to our eyes at least, the citrina shells really stand out,
0:20:08 > 0:20:11and the dark reticulata shells don't stand out so much.
0:20:11 > 0:20:14So I'm going to take four crabs in the citrina shells...
0:20:17 > 0:20:23..and give them the option to move into the empty black shells.
0:20:23 > 0:20:25Now, the other half of the experiment
0:20:25 > 0:20:28is to take four crabs in dark reticulata shells.
0:20:28 > 0:20:29So I'll find those.
0:20:29 > 0:20:32If you fish out four crabs in dark reticulata shells.
0:20:32 > 0:20:36One, two, three, four. There we go.
0:20:36 > 0:20:37We'll put them into here,
0:20:37 > 0:20:40and these guys have the option of moving into citrina shells.
0:20:40 > 0:20:43So these crabs can move into shells that blend in,
0:20:43 > 0:20:46and these crabs can move into shells that stand out.
0:20:46 > 0:20:48Very particular about moving into new shells.
0:20:48 > 0:20:51They want to make sure that a new shell is absolutely better
0:20:51 > 0:20:53than the shell they're coming out of.
0:20:53 > 0:20:55I think he's going to come out. There he goes.
0:20:55 > 0:21:00Swapped shells, there we go. Gone from yellow into dark,
0:21:00 > 0:21:04and I can count here that three of the crabs are in dark shells.
0:21:04 > 0:21:09And blending in well with the background.
0:21:09 > 0:21:12'Whereas the ones in the dark shells stay where they are.'
0:21:13 > 0:21:16What it shows overall if we'd run this experiment lots and lots
0:21:16 > 0:21:21of times, the overall trend would be that significantly more crabs
0:21:21 > 0:21:24would be in the darker coloured shells, and that just goes to show
0:21:24 > 0:21:27how important blending into the background is for these animals.
0:21:29 > 0:21:32'Choosing their shells carefully is a matter of survival
0:21:32 > 0:21:34'for the hermit crab,
0:21:34 > 0:21:37'as this affords it the camouflage and protection it needs
0:21:37 > 0:21:39'to hide from roaming predators.'
0:21:45 > 0:21:47'Anticipating tidal change
0:21:47 > 0:21:50'is a problem all rock pool creatures face.'
0:21:52 > 0:21:55'Dr David Wilcockson of the University of Aberystwyth
0:21:55 > 0:21:58'is going to show me how animals are adapted to cope with this.'
0:21:59 > 0:22:01So the tide is out,
0:22:01 > 0:22:05and the question is how do the organisms on the beach
0:22:05 > 0:22:06know when it is coming in?
0:22:07 > 0:22:09That's actually a very good question,
0:22:09 > 0:22:12because all organisms, including ourselves,
0:22:12 > 0:22:16have biological clocks which enable us to anticipate changes
0:22:16 > 0:22:19in our environment such as night and day,
0:22:19 > 0:22:21and in this case, the incoming and outgoing of the tides,
0:22:21 > 0:22:25and this organism we have buzzing around in these tanks
0:22:25 > 0:22:28is the marine equivalent of the woodlouse.
0:22:30 > 0:22:33It's an animal called Eurydice pulchra,
0:22:33 > 0:22:38and Eurydice has a very good 12.4 hour, or tidal clock,
0:22:38 > 0:22:41whereas ours is run on a 24-hour basis.
0:22:41 > 0:22:45And they come out of the sand and swim when the tide is in,
0:22:45 > 0:22:47and feed and breed, and then what they'll do
0:22:47 > 0:22:51before the tide goes out is actually bury back into the sand
0:22:51 > 0:22:54so they maintain their preferred position on the shore.
0:22:55 > 0:22:57'Maintaining the best position on the shore
0:22:57 > 0:22:59'is essential for survival.'
0:23:00 > 0:23:02'To best illustrate tidal rhythms,
0:23:02 > 0:23:05'David has devised a unique experiment.'
0:23:05 > 0:23:09So what we have here, Richard, is activity monitors,
0:23:09 > 0:23:13and in each tube is a little bit of sand and some seawater,
0:23:13 > 0:23:16and there is an individual Eurydice in each of these tubes
0:23:16 > 0:23:18and they are all inactive at the moment,
0:23:18 > 0:23:21because currently they are expecting it to be low water.
0:23:23 > 0:23:26When they expect high water, they will start to swim,
0:23:26 > 0:23:29and across each tube is a little infrared beam,
0:23:29 > 0:23:33and when they swim through that beam, the beam is broken
0:23:33 > 0:23:37and the beam break is recorded on the computer.
0:23:37 > 0:23:38I see.
0:23:38 > 0:23:40We can actually turn those recordings into plots,
0:23:40 > 0:23:42so we can visualise the activity,
0:23:42 > 0:23:47and this is a plot from one individual Eurydice,
0:23:47 > 0:23:49and you can see these black bars here
0:23:49 > 0:23:52represent beam breaks or activity periods,
0:23:52 > 0:23:55and these bouts of activity are occurring every 12.4 hours.
0:23:55 > 0:23:57On the nail.
0:23:57 > 0:23:59A very precise 12.4 hour rhythm,
0:23:59 > 0:24:01so we can actually show they have a tidal rhythm,
0:24:01 > 0:24:04and the important thing is that this rhythm will continue
0:24:04 > 0:24:06in the absence of any tides.
0:24:15 > 0:24:19'The tide outside has now risen, and there is a definite change
0:24:19 > 0:24:20'in activity of our subjects.'
0:24:22 > 0:24:23Well, there's an amazing sight.
0:24:23 > 0:24:26It's been a few hours since we looked at them last,
0:24:26 > 0:24:28and we can see now that they think it is high tide,
0:24:28 > 0:24:30or they're expecting it to be high tide,
0:24:30 > 0:24:34and they're zooming up and down, crossing the infrared beam.
0:24:34 > 0:24:35I can see the numbers going up.
0:24:35 > 0:24:38That's right, and those beam breaks are being recorded
0:24:38 > 0:24:40on the monitor here.
0:24:40 > 0:24:43So, in nature, this is when they'd be feeding and on the hunt.
0:24:43 > 0:24:44That's right, yeah.
0:24:44 > 0:24:49But obviously this internal clock needs some controls on it.
0:24:49 > 0:24:52I mean, are there things in the natural environment
0:24:52 > 0:24:53that help set those controls?
0:24:53 > 0:24:57There are. What happens is that each individual animal,
0:24:57 > 0:25:01its clock will be slightly different to the next one.
0:25:01 > 0:25:04- Their clocks drift out of phase... - Right.
0:25:04 > 0:25:06..with the natural cycle, if we remove it
0:25:06 > 0:25:08from its natural environment.
0:25:08 > 0:25:10So the incoming and outgoing tide
0:25:10 > 0:25:13actually re-synchronises their clock.
0:25:13 > 0:25:16Life in rock pools is more complicated than we thought.
0:25:16 > 0:25:19I think it's far more complicated than we thought, yes.
0:25:26 > 0:25:29Creatures of the rock pool provide one of the most sensitive
0:25:29 > 0:25:34barometers to monitor the way our natural environment is changing.
0:25:36 > 0:25:40'Like all intertidal animals, barnacles have to deal with
0:25:40 > 0:25:43'fluctuating conditions on both a daily and seasonal basis.'
0:25:46 > 0:25:50'However, recent research suggests that barnacles and other creatures
0:25:50 > 0:25:54'have to cope with changes over a much bigger timescale.
0:25:54 > 0:25:57'Changes that we may be responsible for.'
0:25:59 > 0:26:03'Nova Mieskowska of the Marine Biological Association
0:26:03 > 0:26:08'has been analysing long-term data on barnacles here in Devon.'
0:26:09 > 0:26:13We've found over the many decades that we've been studying barnacles
0:26:13 > 0:26:17all around the UK, but especially down in the southwest here,
0:26:17 > 0:26:20that the warm water barnacles, which you can see around here
0:26:20 > 0:26:24with the slightly more greenish tinges, they're kite-shaped.
0:26:24 > 0:26:27These warm water barnacles have become a lot more abundant,
0:26:27 > 0:26:30especially over the last 20, 25 years since climate change
0:26:30 > 0:26:33really started to take hold.
0:26:33 > 0:26:34Their northern limits are in Scotland
0:26:34 > 0:26:36for the warm water barnacles,
0:26:36 > 0:26:38and they go all the way down south,
0:26:38 > 0:26:41past the Mediterranean and slightly into north Africa
0:26:41 > 0:26:43whereas the cold water barnacles,
0:26:43 > 0:26:46these are the ones that are slightly whiter.
0:26:46 > 0:26:49Here's one. You can see. This is Semibalanus Balanoides here.
0:26:49 > 0:26:52Oh, I can see now, yes. You have to get your eye in, don't you?
0:26:52 > 0:26:56Their northern limits go way up into the Arctic Circle,
0:26:56 > 0:26:59but their southern limits have been cut back and back further north.
0:26:59 > 0:27:02They used to be in northern Spain around the Bay of Biscay,
0:27:02 > 0:27:04where there has been a big trimming northwards
0:27:04 > 0:27:08because it's just plainly too warm for them to live there any more.
0:27:08 > 0:27:11And we're even seeing the effects here in the southwest.
0:27:11 > 0:27:12We've seen a massive decline
0:27:12 > 0:27:16in the survival of these cold water barnacles.
0:27:16 > 0:27:17And have we got their natural predators
0:27:17 > 0:27:19dotted around on the surface?
0:27:19 > 0:27:23Yes. You can see that we've got some marauding dog whelks,
0:27:23 > 0:27:25and these dog whelks do preferentially
0:27:25 > 0:27:28eat the cold water barnacles Semibalanus Balanoides,
0:27:28 > 0:27:30so it will be very interesting to see whether,
0:27:30 > 0:27:33when we lose these for good in the southwest,
0:27:33 > 0:27:35whether the dog whelks will actually be able to change
0:27:35 > 0:27:39and then feed entirely on the warm water barnacle or not.
0:27:39 > 0:27:42Well, I guess the story of evolution is often change or die.
0:27:42 > 0:27:43Yes.
0:27:46 > 0:27:48It is alarming to think that we might be responsible
0:27:48 > 0:27:53for affecting the survival of the creatures we know and love so well.
0:27:56 > 0:27:59However, because they have adapted to one of the toughest places
0:27:59 > 0:28:04on Earth, rock pool animals have outlived many other species
0:28:04 > 0:28:06they shared the seas with.
0:28:06 > 0:28:10'As a palaeontologist, I marvel to think that their ancestors
0:28:10 > 0:28:13'lived alongside fossil species I have studied,
0:28:13 > 0:28:15'but whose lives I can only really imagine.'
0:28:17 > 0:28:21'And rock pool animals may well outlive us.
0:28:21 > 0:28:25'For if anything has got what it takes to endure, it is them,
0:28:25 > 0:28:28'for they are masters of an ever-changing environment.'
0:28:52 > 0:28:55Subtitles by Red Bee Media Ltd