All language subtitles for The Secret Life of Rock Pools BBC 720p HDTV EN Sub_Subtitles01.ENG

Every day when the tide retreats,
a secret world is exposed.

A magical and intriguing place

full of remarkable
and unusual characters.

The rock pool
is a cornucopia of life.

It's full of diverse animals.

Some we're familiar with,
some we're not.

There's a nice little cushion star,

there's a shrimp,

there's a dog whelk,
there's a top shell.

There's a little pipefish
wiggling about.

There's a porcelain crab.

All of these animals have
their own ecological parts to play

in the life of the rock pool.

But this unique environment

experiences some of the most extreme
conditions in the natural world.

My name's Professor Richard Fortey
and like everybody else,

I just love rootling
around in rock pools.

But I'm a palaeontologist,
so for me, rock pools are more

than just a collection of wonderful
and interesting animals.

They also provide
a window into the past.

Part the weeds on any rock pool,
and you open the curtains

onto a life and death drama
that has been played out

for hundreds of millions of years.

Some of the creatures that live here
have outlived the dinosaurs

and have evolved truly extraordinary
adaptations to survive.

I want to show you
how rock pool creatures

have stood the test of time.

We have created
our own rock pool laboratory

deep in the heart of the National
Marine Aquarium in Plymouth.

Here, under the guidance of some of
Britain's leading marine biologists,

we will take a closer look
at rock pool creatures

and reveal just how
they have evolved to cope

with the ever-changing tide.

Life in rock pools is more
complicated than we thought.

I think it's far more complicated
than we thought.

We will investigate how
they compete for food and space...

There are specialised tentacles
simply for fighting.

..and reveal the surprising
behaviour they use

to fight off predators.

It's really very agitated.

It becomes like a sort
of animated mushroom.

This is The Secret Life
Of Rock Pools.

It's high tide and the little world
of the rock pool

is connected to the greater
world of the ocean beyond.

It's a good place to be.
There's normal salinity,

there's plenty of oxygen
and above all,

there's nutrients coming in
from beyond.

And yet, it's not
going to last for long.

In a few hours,
everything will change.

As the tide falls, life becomes very
different for the creatures here.

The exposed shore is now subject
to unpredictable changes.

Changes that depend on the weather,
the time of year,

and the time of day.

Here, temperatures can
range from freezing to baking,

oxygen levels fluctuate and salinity
can increase or decrease,

causing body tissues to dehydrate
or swell with water.

But before any of these changes
even begin to come into play,

there is a more immediate problem.

There is now less room
for everyone to live

and resources are diminished.

Everything is dictated
by competition.

Finding a good position becomes
a matter of life or death

for all the creatures here.

For anemones, it is important
to have a good spot

to catch the most food.

Anemones appear sedentary,
but they do move around very slowly.

To find, secure and defend the best
spot, they have a secret weapon.

And to shed some
light on their lives,

Dr Mark Briffa of the University
of Plymouth has come into the lab.

So, Mark, sea anemones
are beautiful creatures,

but most people might think
that they're pretty inactive.

They just sit there
waiting for food to come along.

Yes, they are relatively slow-moving
animals, but they are animals,

and that means
they have to consume food.

And one of the things sea anemones
have to do before they can consume it

is to capture their food.

Can you see the feeding tentacles?

There are six rows of tentacles
on the top of the animal,

192 in total. And just by looking
at them for a small amount of time,

you can see that the tentacles
are moving about

and these tentacles are there
to trap food and bring it in

towards this structure
in the middle of the animal.

This is the oral disc.
Otherwise known as a mouth.

A mouth, yes.

And they ingest the food through
their oral disc, or their mouth.

They have two different types of cell
which will help them trap food.

Nematocysts are stinging cells
common to all anemones

and jellyfish.

When stimulated,
they fire a venomous dart

attached to a thread
into their prey.

We can look at the use
of the tentacles to trap food

by taking a small piece of food,
this is a little piece of limpet,

and dropping it over
the ring of tentacles.

They kind of close in on it
and pull it down.

Oh, it likes that.
It likes that a lot.

We've got a very hungry
anemone here.

It's closing all of the tentacles,
all six rings.

It's closing them in to push the food
back down towards its mouth.

And they're not just
for trapping prey either.

In this species of sea anemone,
there are specialised tentacles

simply for fighting.

And these specialised tentacles
appear as little blue beadlets

in a ring around the outside
of the six feeding tentacles.

Hence the name "beadlet".

That's where it gets its name from,
yeah.

And they will use them in combat
with rival anemones

who are of the same species
and therefore require exactly

the same resources in terms
of a good place in the rock pool.

Using a specialist
time-lapse camera,

we can speed these battles up
to see what's really happening.

Twisting their flexible bodies,

anemones take aggressive swipes
at each other,

tearing off ribbons of skin.

Losers have no choice
but to find another place to settle.

We may barely give anemones
a second glance,

but their remarkable fighting
behaviour has allowed them

to colonise the most sought-after
locations in the rock pool

and has helped them
thrive on our beaches

for around 540 million years.

Other creatures have dealt with
the lack of space very differently.

They have left the pools
altogether, taking up residence

on the rocks, where they
are exposed at low tide.

Around 530 million years ago,

molluscs developed hard shells
to house their soft body parts,

creating a microclimate
into which they could retreat.

And one of the first animals to do
this is still with us.

It's a living fossil. The chiton.

The chiton has a number of plates
which allow it to shuffle around

and grip tightly to the surface
of the rock.

But an even more effective way of
doing this is under a single shell,

and the mollusc that has done
this most successfully is still

with us in every rock pool
and every rocky shore.

It's the limpet.

Apart from clinging steadfastly
to rocks,

limpets play an important part in
the ecology of the rocky shore.

They too have to compete
for resources.

Professor Stephen Hawkins,
of the University of Southampton,

is a limpet expert.

You might think that a limpet
is a limpet is a limpet,

but actually we've got
three British species.

We do have three British species,
we have...

These are all patella vulgata.

And nearby, we also have
patella depressa,

which is a Southern species
of limpet and it goes from Senegal

up to North Wales.
And underneath here, I know there's

a patella aspera - they have a nice
hat of seaweeds on top of them.

And there it is. And there it is.

I'm told that they vary
in conicality according to where

they are on the shore.
Yes, and also with age.

I think as they get bigger and older,
they tend to get more conical

and it makes quite a lot of sense
to be conical like this,

because the circumference
is where water gets lost

when the tide's out, so there's more
of an animal contained,

there's more biomass contained,
within a more conical limpet

than, say, a flatter one,
or a younger one.

What about hiding under these weeds?

Well, different species have
different habits.

Patella vulgata actually likes
to shelter under seaweed.

They can actually munch away
at the bases of the seaweeds

and even, by feeding at night,
sort of gnaw away on the ends.

'So what physiological adaptation
allows limpets to hang on

'like the proverbial limpet?'

They've got a big extensive foot.
You can see on this animal here

and essentially it's
a very complicated

biological suction device.
That's how it works.

I mean, I notice most of the limpets
seem to be on the rocks,

but are they in the rock pools
as well?

You do get...

some limpets in rock pools.

The juveniles settle
out of the plankton

and actually settle in rock pools.
Is that one there? That's one there.

And they get attracted by chemicals
in the pink algae that are in

this rock pool.
It's a very good indication

of what's a nice place to settle,

and the limpets use these
rock pools as a nursery ground

for the first year
or so of their lives.

And then they move up
onto the barer rock surfaces?

They move up. And they're quite
vagrant when they're young, but once

they get to 15-20mm, then they start
homing on a fairly regular basis.

Surprisingly, limpets
are territorial.

They create a depression in the rock
known as a home scar.

As the tide starts to go down,
they return to this place

and hunker securely down.

Territorial fights are common,
and losers are prised off the rock.

I think limpets are really neat,

and they're a great experimental
animal to work with.

They're so interesting and they
move, but they don't move too far,

and you can do all sorts
of things with them.

I'm afraid I'm rather
fond of limpets.

Well, I've become a fan too.

As the tide covers them,
limpets leave their home scars

and begin to feed.

Limpets are very important
grazers on the seashore.

However, there is intense
competition.

To investigate further, we have
to go back into the laboratory.

Stephen, you were up early this
morning collecting us some limpets.

Yes, I collected these this
morning at low tide just as the tide

was about to come over them,

so we should be able to stimulate
them to set off on their

foraging excursions, to go off
feeding, if we put them in the tank.

It doesn't take long before they
sense they're surrounded with water.

Yes, when the tide is out they're on
a home scar, which they create

in the rock, which their shell
fits really well.

One of the limpets
is still on its home scar,

but the other is off and raised up.

Little tentacles coming out?

Yes, they have these fantastic
sensory tentacles all the way around

the edge of the shell.

The big ones, the primary tentacles,
actually match with those rays

you can see on the shell,
and there's smaller tentacles

in between, and that gives lots
of information about the physical

and biological environment
when they're out foraging.

And foraging means scraping algae
and other things

off the surface of the rock.

That's right, they feed by scraping
the rock surface

using their radula, yes.

The radula of the limpet
is a ribbon-like tongue

covered in teeth.

It moves back and forth scraping
algal slime from the rocks.

The limpet's radula is tipped with
haematite - an extremely hard

material that allows the limpets
to graze on hard surfaces.

So what's the consequence
of that?

'Stephen's research has shown
that limpets have a profound effect

'on the ecology
of the seashore.'

When they're off foraging, and this
is where I fenced the rock

to keep limpets out, and all the rest
of the area here is where

limpets were able to forage freely,
and just six months later... Wow.

Yes, it's amazing, isn't it?

Just six months later there's a
really dense growth of seaweeds,

bladderwrack, fucoids covering
the rock in the absence

of the limpet grazing,
so basically the limpets,

through their radulae,
really control the algae.

Limpets are synonymous with rock
pools, but through millions of years

of evolution, they have pushed back
the boundaries and have left

the pools to colonise the rocks
along the shore.

The rising tide not only gives
limpets an opportunity to feed -

it brings with it danger.

Starfish.

Starfish belong to a phylum
of animals called the echinoderms,

which first appear in the fossil
record more than 500 million
years ago.

Starfish have macabre eating habits.

Using their strong, sticky tube
feet, they force open the shells

of molluscs and then,
pushing their stomach out

through their mouth,
they digest the animal inside.

Limpets have been locked in an arms
race with starfish for millions

of years, and have evolved their own
way of dealing with them.

So, what are we looking for here?

What happens, usually, is that
the limpets get agitated

when they sense a predator
in the area and then,

when the starfish is in contact
with the limpet, the limpet tends

to raise up, and then it will
often stamp down on the starfish

and maybe drive it off.

Let's see if that behaviour happens.

In a rock pool, there is nothing
quite as sinister

as a marauding starfish.

Small limpets have no choice
but to flee.

A lucky escape.

Large limpets, however,
stand their ground.

'Using the edge of the shell,
a limpet can push the starfish away

'to prevent it climbing on top.'

Look at that!

'Continually scraping at the arm
can damage the tube feet,

'deterring an attack.'

I don't think I'd like to be
approached by a great battery

of wiggly tube feet,
if I was a limpet.

Didn't think they did this behaviour.
There he goes, look at that.

It's really very agitated.

It becomes like an animated
mushroom in the end, doesn't it?

Well, we can't say that
rock pools lack drama.

I'll never look at limpets
in the same way again.

Beneath that implacable shell
hides a strong personality.

Unseen by us, their battles
with starfish have been fought

beneath the waves for millennia.

But it is not just limpets
that have to face predators.

All the creatures
in the rock pool must be

constantly on their guard,
and have evolved many different ways

of dealing with potential
attackers from land and sea.

The majority of molluscs
living around rock pools rely on

their hard shells
for protection against predators,

but not all of them do so.

This orange blob is actually a sea
slug, and it's protected because

it absorbs toxins from other
sources, in this case the sponges

that it eats. So in spite
of its vulnerable appearance,

it's actually rather well
protected against predators.

It's pressure from predators
that has encouraged them to evolve

these incredible defence mechanisms.

This is a lemon sea slug.

Even more remarkable
is the sea slug elysia.

It sucks in rock pool algae

and keeps the photosynthetic cells
alive, providing energy

direct from the sun.

This rare Celtic sea slug,
found in rock pools around the UK,

is unusual in that it is descended
from terrestrial slugs.

It is often found grazing out
of the water as well as under it.

At high tide, the rock pools
are sometimes visited

by another mollusc.

But this mollusc
couldn't be more different

from its relative, the sea slug.

It is a fast-moving killer -

the cuttlefish.

Cuttlefish belong to a class
of molluscs called cephalopods

and are widely considered

to be the most intelligent
of all invertebrates.

I think they are the ultimate
rock pool predator.

At the Marine Biological Association
in Plymouth

I have a great opportunity
to get up close and personal

with these magnificent animals.

The ones here are kept
for fisheries research

and are easily trained
to take food from my hand.

Wonderfully accurate vision.

Tentacles at the front,

two of which are modified
to grasp the prey.

They also have remarkable
colour-changing abilities.

This colour change
is often used for camouflage,

allowing them to sneak up
on unsuspecting prey.

They're hiding
in little tubes down there,

which are obviously there
for their comfort, so they can lurk.

And when food comes around,
well, out they pop.

Let's see if we can get the bigger
one to come up this time.

Come on, you know you want it!

Whoa! It inked me!

Cuttlefish are one of the largest
predators to visit the rock pool.

Some rock pool predators though

are far less conspicuous
but no less deadly.

This is a dog whelk.

A fearsome predator
in the rock pools.

Unlike its limpet cousins,

this carnivore has devised
an ingenious way

of hunting other molluscs.

And one of its favourite prey
are mussels.

Mussels are filter feeders,

sieving off the abundant food
that drifts in the upper ocean.

They attach themselves
to the rock surface

by strong threads which they secrete
through their muscular foot.

These threads enable them
to cling to the rocks

despite the relentless pounding
of the ocean waves.

However, the stationary mussel is an
easy target for prowling dog whelks.

Their radula is specially modified
to drill through the shells

to reach the soft flesh
of the mussel.

It's a gruesome attack.

Mussels, however, can turn
the tables on a dog whelk.

Sensing a nearby attack,
others in the colony

start to produce
more and more sticky threads.

If they make contact, it can
spell doom for the dog whelk,

which will starve to death.

The hard shell of molluscs
like the dog whelk

persist long after

the soft parts of the animal itself
have decayed away.

But these empty shells
don't go to waste.

In the rock pool,
when one species dies or moves on

another takes over.

Empty shells are put to good use

by one of my favourite rock pool
creatures, hermit crabs.

Hermit crabs use shells as a very
effective defence against predators

and their bodies have evolved
to fit them perfectly.

Unlike other crabs, their abdomen
has become soft and asymmetrical

and their back legs
are very reduced,

allowing them to fit inside shells.

The asymmetry of their claws

also allows them to close up
the entrance to the shell

as a defence against predators.

The crab's shell must not only be
tough enough to withstand an attack,

but must also afford it
some camouflage.

Dr Mark Briffa from Plymouth
University has returned to our lab

to demonstrate how crabs
go about choosing shells.

Well, nothing in nature is wasted
and that goes for our shells too,

because here they are
with a new occupant.

That's right. The common
European hermit crab.

What's happened
in hermit crab evolution

is that they've become adapted
to occupy this free resource.

So they're taking advantage
of somebody else's hard work,.

That's right.
The snail has put all the effort

into growing these shells,

which means that
the hermit crab doesn't have to.

And how big do they grow?

Well, these are the sorts

that are the size of hermit crabs
that you'll find in rock pools.

This guy...

is the same species.

My goodness!

These tiny little guys and
this monster. They're all adults.

Shall I pop that one in here
so we can see him come out?

You can see the contrast in sizes.

Sort of orders of magnitude,

bigger than these tiny little
intertidal specimens.

Pushing some of the smaller guys
out of the way.

This is really as big as the common
European hermit crab will get.

So these shells are obviously
a protection. That's right.

But are the crabs even choosier

about which types of shells
they pick up?

The crabs are incredibly choosy
about what they want.

They'll spend a lot
of time and effort

deciding whether to change shells,

whether a potential new shell
is a good one.

They're also known to be particular
about the colour of the shell,

at least in terms of its contrast
against the background.

We can run a little experiment here,

So, what I have are two containers
with a dark-coloured substrate

and I have some
Littorina obtusata shells.

These are called citrina
and dark reticulata.

The only thing that's really
different about them is the colour.

What I'm going to do
is place these shells,

so you can see straight away that,
to our eyes at least,

the citrina shells
really stand out

and the dark reticulata shells
don't stand out so much.

So, I'm going to take four crabs
in the citrina shells.

And give them the option to move
into the empty black shells.

Now, the other half
of the experiment

is to take four crabs
in dark reticulata shells.

So, I'll find those.

If you fish out four crabs
in dark reticulata shells.

One, two, three four.

We'll put them into here,

and these guys have the option
of moving into citrina shells.

So, these crabs can move
into shells that blend in.

These crabs can move
into shells that stand out.

Very particular about
moving into new shells.

They want to make sure that
a new shell is absolutely better

than the shell
they're coming out of.

I think he's going to come out.

There he goes.
He's swapped shells. There we go.

He's gone from yellow into dark.

And I can count here

that three of the crabs are
in dark shells on this stage,

blending in well
with the background.

Except for that stubborn one there,

which, of course, has stayed
obstinately in a yellow shell.

Standing right out
against the background.

Maybe it hasn't
made its decision yet,

maybe it hasn't spotted
that the shell stands out.

It might have just got it wrong.
What it shows overall,

if we had run this experiment
lots and lots of times,

the overall trend would be

that significantly more crabs would
be in the darker-coloured shells.

And that just goes to show
how important

blending into the background,
or crypsis, is for these animals.

'And it's not just camouflage

'that's important as a defence
against predators.

'The shell must also fit well

'if it is to give the crab
the best chance of survival.

'Because of this, there is intense
competition for shells.'

OK, so here we are.

These crabs have been isolated
for about 16 hours.

We're going to use this tank
as an arena to stage a fight in.

And this large crab is in a shell
that's too small for it.

It's uncomfortable.
It doesn't fit in there very well.

It's trying to withdraw
but the claws are still exposed.

So let's put him in there.

This is a smaller crab

and you can see he's withdrawing
right into that shell.

He's shaking around
in a rather loose coat.

He's got a very, very
spacious house.

So we've got a big crab
in a shell that's too small

and a little crab in a shell that
is just right for the big crab.

'The large crab adopts
intimidation tactics

'in an attempt to make
the smaller crab leave it's shell.'

It's a little bit like
a war of attrition.

Who can keep going for the longest.

Will the attacker wear itself out
with the shell rapping

before the defender
decides to give up.

Here we go.

Eviction! So the attacking crab
just evicted the defending crab.

The attacking crab
has gone into the shell

that it's just pulled
the defending crab out of,

and it's trying to
keep the defending crab...

No, the defending crab
has now gone into the shell

that the attacking crab vacated.

But not putting up
much of a fight, I have to say.

Well, you're not going to
hang around without a shell

if you can possibly avoid it.

Hermit crabs are
an evolutionary marvel,

perfectly adapted to recycle
the discards of another species

as a defence against predators.

As well as competing for space
and avoiding attack,

other creatures have evolved
remarkable adaptations

to deal with
the ever-changing environment.

Well, the tide's now really out

and this place has become
quite a hostile environment.

Everything's drying out.

You'd think that
any organism with any sense

would have retreated out to sea
with the ebbing tide,

and yet, hiding away here,

is something really extraordinary.

It's a fish.

A blenny.

Not just one, but several,
hiding away in a crack in the rocks.

They have chosen not to
retreat with the tide,

but to stay and risk life
as a fish out of water.

Gulping air, they absorb oxygen

through blood vessels
in their oesophagus.

It will be six hours or more
before the sea returns

and they can resume
their normal fishy lives.

By staying put
when the tide retreats,

a blenny does not
leave its territory

and does not have to
compete for a new one

every time the tide returns

and it also avoids larger predators
it might encounter at sea.

But they must return to
their chosen rock crevice

before the tide retreats.

Timing it wrong could be fatal.

Anticipating tidal change

is a problem
all rock pool creatures face.

Dr David Wilcockson
of the University of Aberystwyth

is going to show me how animals
are adapted to cope with this.

So, the tide is out,

and the question is

how do the organisms on the beach
know when it's coming in?

That's actually
is a very good question,

because all organisms, including
ourselves, have biological clocks

which enable us to anticipate
changes in our environment,

such as night and day,
and in this case,

the incoming and outgoing
of the tides.

And this organism we have
buzzing around in these tanks

is a marine equivalent
of the woodlouse.

It's an animal called
Eurydice pulchra.

And Eurydice has a very, very good
12.4-hour or tidal clock,

whereas ours is run
on a 24-hour basis.

But they come out of the sand
and swim when the tide is in

and feed and breed,

and then what they'll do
before the tide goes out

is actually bury
back into the sand

so they maintain
their position on the shore,

their preferred position
on the shore.

'And, as we have seen, maintaining
the best position on the shore

'is essential for survival.

'To best illustrate tidal rhythms,

'David has devised
a unique experiment.'

So, what we have here, Richard,
is activity monitors,

and in each tube is a little bit
of sand and some seawater

and there's an individual Eurydice
in each of these tubes

and they're all inactive
at the moment

because currently they're
expecting it to be low water.

When they expect high water,
they'll start to swim

and across each tube
is a little infrared beam.

And when they swim through
that beam the beam is broken

and the beam break
is recorded on the computer.

We can actually turn
those recordings into plots

so we can visualise their activity,

and this is a plot from
one individual Eurydice.

And you can see these black bars
here represent beam breaks,

or activity periods.

And these bouts of activity
are occurring every 12.4 hours.

On the nail.

A very precise 12.4-hour rhythm.

So we can actually show
they have a tidal rhythm,

and the important thing is

that this will continue
in the absence of any tides.

The tide outside has now risen

and there is a definite change
in activity of our subjects.

Well, there's an amazing sight.

It's been a few hours
since we looked at them last

and we can see now that
they think it's high tide,

or they're expecting it
to be high tide,

and they're zooming up and down,
crossing the infrared beam.

I can see the numbers going up.
That's right.

And those beam breaks are being
recorded on the monitor here.

So, in nature, this is when
they'd be feeding and on the hunt,

but obviously this internal clock
needs some controls on it.

I mean, are there things
in the natural environment

that help set those controls?

There are. What happens is
that each individual animal,

its clock will be slightly
different to the next one.

Their clocks drift out of phase
with the natural cycle,

if we remove it from
its natural environment.

So the incoming and outgoing tide
actually resets their clock.

It re-synchronises their clock.

Life in rock pools is more
complicated than we thought.

It's far more complicated than
we thought, yes.

The ability to anticipate
the changing tide is essential.

Knowing when to feed, breed or hide
is vital for any creature

living on the shore.

As the tide changes,
so do conditions on the beach,

and this has a profound on all
living things - even the seaweeds.

For more than a billion years,
life on Earth was dominated by very

simple single-celled organisms
slime, if you like.

This rock's covered in it.

But those organisms included
photosynthesizing blue-green

bacteria called cyanobacteria that
form living films and breathed

oxygen into the atmosphere, thereby
transforming the early Earth.

And about 1.3 billion years ago,
they were joined by much larger

multi-celled organisms algae.

Doing the same job,
still photosynthetic,

but these today dominate what we see
on the beach and in the rock pools.

Of course, most people know it
simply as seaweed.

With more than 9,000 species
of seaweed in the UK alone,

the sheer variety
and volume of them is staggering.

A quarter of the total global energy
captured by photosynthesis

is fixed here
in the intertidal zone.

So seaweeds are the basis of a rich
and complex food chain.

Seaweeds show a distinct pattern
of colonisation,

from the upper to the lower shore.

This is known as zonation,

and gives us a visual indication
of how conditions vary.

But what causes zonation
and why is it important?

Professor Colin Brownlee
of the Marine Biological Association

is going to demonstrate.

These seaweeds grow on the rocks
as you know, and they produce eggs

and sperm, just like animals,
and they're produced into the

sea water and the eggs are fertilised
by the sperm and what they want

to do is sink to the rock surface
and then attach where they can grow.

We can analyse a sample of sea water
under the microscope.

So what can we see here?

The large round cells are the eggs.

Each one of those is a single egg

and all those small little creatures
swimming around them are the sperm.

Over the next day, the fertilised
eggs develop into embryos.

So this is what they look like
after about 24 hours.

They're no longer spherical eggs.

It's a pear-shaped embryo
and it's protruded a little rhizoid.

It's a tiny little root.

All seaweeds get a chance
to colonise the beach,

but one factor deciding
survival is rainfall.

Remarkably, fresh rain water can
kill some seaweed embryos.

And we can actually try
to demonstrate that now,

just by adding some dilute
sea water to this dish.

It's wobbling a bit as I add it.

It's twitching.

That's me dropping water onto it.

Good Lord! That's dead.

That is one seaweed less.

Fresh water penetrates the cells
by osmosis,

causing them to swell and burst.

And the difference between different
species and how they swell

really determines where
they can survive on that shore.

So there is a constant
bombardment of microscopic seaweed

embryos upon the shore,

and order is only
maintained by relative salinity.

Seaweeds provide food and shelter
for many other creatures.

They are the basis upon which much
life in the rock pool depends.

The rock pools highest up
the beach are exposed to the air

for the longest.

Sunshine causes evaporation
that, in turn, causes the salinity

of the pools to increase
and the temperature to rise.

Oxygen can fluctuate throughout
the day and night.

Here, everything is pushed
to its very limit.

Most active animals choose
to abandon the highest rock pools.

But one of our rock pool favourites
has evolved a unique biology

that has allowed it to survive
further up the shore.

Crabs are arthropods, which means
they have jointed legs

as well as this hard exoskeleton
which encloses their body.

It allows them to tolerate
conditions that other animals

might find difficult.

Of course, arthropods have
been around for a very long time.

In fact, my own favourite organism,
the trilobite,

is an arthropod,
sadly long extinct.

They died out about
250 million years ago,

but their relatives,
the crustaceans, prospered.

And it has to be said
that if you have an exoskeleton,

you also have one particular
drawback.

If you want to grow, you have to
moult and then you're vulnerable.

Prior to moulting, a crab secretes
enzymes to separate the old shell

from the underlying skin.

The crab then absorbs sea water,
causing the old shell to come apart

at a seam that runs
around the body.

The carapace then opens
up like a lid

and the crab extracts
itself from the old shell.

At this time, crabs are extremely
vulnerable and will usually hide,

but moulting is also
essential for another function.

Crabs don't just need to moult
when they want to get larger,

they also have to moult
when they want to mate.

To investigate this further
I have invited Dr David Wilcockson

back into the lab.

David, what's going on?

Well, Richard the female crab
has to be soft,

she has to have just moulted in order
for the male to transfer sperm.

So that's a soft-shell crab stage.

Yes. So she's very vulnerable at
this stage. She's quite immobile.

She's very soft and makes a nice meal
for a predator,

so the male crab will
actually guard her.

He'll embrace her like this,

and the female opens her abdomen,
that's the flap

on the underside of her body,
and the male also opens his abdomen,

and they transfer sperm through a
pair of modified legs from the male.

The male will detect the fact that
she's coming into moult

because she releases pheromones and
he'll stand over her and cradle her.

When she moults, he then flips her
over and they copulate,

and he'll continue to guard her
for quite a number of days,

maybe up to ten days or more.

So if anybody finds a pair of crabs
like this,

the message is "put them back".

Absolutely, yes.

So I can actually show you a neat
trick here in the lab

with the pheromone from females.

I've got here some water that I've
collected from an aquarium

that's contained female crabs
that are coming into moult

and I've got an inanimate
stone from an aquarium.

If I drop that into a tank over here,
we might be able to see

the male crab responses.

So he's scented the stone
and he's up on tip toes.

He's started to cradle.

He's definitely attracted to it.

Oh, dear. Poor crab.

Fancy having
a piece of stone for a partner.

Of course, this is all driven by
the pheromone, this behaviour.

This strong reaction to the scent
a female gives off

when she moults changes the male
from potential attacker to defender.

This is vital
if crabs are ever going to mate.

So what happens next
is the question?

So the male crab has transferred
his sperm to the female

and the female will now produce eggs
which are fertilised,

and if I can just disturb them
gently...

She's not very keen to be disturbed.

Not keen at all.

So we can see, I'm trying not to take
them apart,

the female abdomen is open there,

and underneath there, she will
produce a very big mass of eggs.

We call them berried females.

The eggs females carry
look like small round berries.

They can carry this egg mass
for several months.

They eventually develop into
free-swimming larvae,

which feed among the plankton
for up to three years

before settling
on the seabed as juvenile crabs.

So you may find what you think is
a berried female on the shore

but actually it may not be,

and I've got something really quite
interesting I found earlier.

Sounds intriguing.

This is a shore crab again...

If I can just pick it up,

and on the underside we have what
appears to be an egg mass.

It looks like a berried female
but in actual fact,

if we look more closely,
this is a male crab,

and this egg mass
is a parasitic barnacle.

How on Earth do you know that?

We know it's a barnacle only
because of its larval stage.

It has the same larvae as all
the other types of barnacle.

It's only a millimetre or two
long?

Very small, yes, and the larvae
actually penetrate into the body of

the crab and sends out rootlets into
the body parts and absorbs nutrients.

It takes over the crab.

It's like something out of Alien.

It's converting the crab
into a machine

for producing more
parasitic barnacles.

That's exactly what that egg mass is.

After the invasion of sacculina,
the crab is unable to perform

its normal function of moulting.

Sacculina interferes with
the male crab's hormones.

It becomes sterile and even begins
to behave like a female.

It's hard to believe that such
a frankly disgusting creature

is related to the most abundant
things you find on practically every

shore, the regular barnacle.

It's very different, yes.

Crabs are a rock pooling favourite
but few can imagine how complex

and interesting their world
really is.

As well as their fascinating
reproductive cycle,

crabs have evolved to thrive in some
of the most extreme environments

on the rocky shore.

To explore the lengths some animals
will go in order to survive

in the most extreme
conditions of the rock pool,

I'm going on a little adventure.

Something I've never done before
night rock pooling

with Dr John Spicer
of Plymouth University.

I think at night it's more exciting

because things happen
much more quickly.

There's a lot going on and if you've
got a little bit of patience,

you can see so much,
even in a small pool like this.

It is a busy, violent,
exciting place.

One of the really nice things
about night is the fact that

even animals which would normally
be submerged,

because it's quite humid at night,
will come out and they will scuttle

across the rocks.

For instance if you look really
carefully, you can see

the shadows of little crabs as
they run from crevice to crevice.

They're no longer in the water
but as long as they're damp,

their gills are such that
they can still breathe

when they're out of water.

Although this is good news, this is
water when the water's gone.

It's a little refuge, a little sea.

It's still got its own problems.

At night, the plants are no longer
photosynthesizing.

The plants
and animals are using the oxygen

and so the oxygen declines
throughout the night.

Sometimes down to zero.

So you might finish up with
somewhere that's

extremely unpleasant for life.

It's one of the prices of
staying hydrated.

You have to put up with real
severe extremes of oxygen,

so if I take some water from this
rock pool, which should be

quite low in oxygen, we can take it
back to the laboratory,

and we can actually use it
in the laboratory

and see the response of some
of the creatures that live here

to that low oxygen water.

There's plenty of water in there!

Just don't spill it.

So, Richard, what I'm going to do
is actually here in the laboratory

set up an experiment with two
artificial rock pools.

And which species are we using?

Now, the animal we will use is
an animal called Palaemon elegans,

which sounds very grand.

It's a common glass shrimp, where you
can see all the inner working parts.

It's very beautiful.

And you're pouring
the water in slowly

cos you don't want to alter
the oxygen.

That's right.
The oxygen will alter by itself.

If we do it nice and slowly,
it should take a while to alter.

Now we'll bring
the shrimp across.

Here they are - Palaemon elegans.
Relatives of the common prawn.

This one used to be fished
commercially off Britain.

At least, its big brother did.

These particular shrimps you only
find intertidally in tide pools.

They're the ones you often see
almost colourless against the sand.

Yeah. They can change colour
within a few minutes.

Quite busy at the moment.

They're normally extremely
active animals.

We just have to leave them to settle
down a bit down now,

and see what happens.

Because it is found in the higher
rock pools, where the biggest

changes in oxygen occur, the glass
shrimp has evolved a unique

behaviour that we can see
in the laboratory.

You'll notice that it's now
crawled onto the rock here

and by lying on the side, it has
a partial immersion response.

It's not totally out of the water,

so it's actually making oxygen
come into the water by beating its

back limbs and also inside its gill
chamber, it's got a little device

called a scaphognathite, which is
beating and oxygenating the water.

If they were totally out of the
water, the gills would collapse

and it suffocates. If it
stays in the water, it suffocates.

This partial immersion response...

Is a way of keeping
alive in a time of crisis.

That's exactly right.

Its closely-related,
deeper-water relative

Palaemon serratus doesn't do
this behaviour.

So this guy is able to survive
for longer in shallower

and more challenged rock pools
than its close relative.

That's right. And we see that
on the shore.

You go the middle, lower shore,
you get both species.

The high shore
and it's only this one.

So it's a tough little beast.

It is this sort of
ingenious behaviour

that makes rock pool creatures
so resilient

to the extremes of
the intertidal environment.

They've risen to every challenge
that has been thrown at them.

Through geological history,
some of these animals have survived

global catastrophes that have wiped
out much of life on Earth.

With their physiological
and behavioural adaptations,

they have had what it takes
to endure.

But - what does the future
hold for them?

The tide's almost in but there's
still some animals that can survive

having been out of water for
more than half the day.

And the last toughest ones
are barnacles,

and when the sea finally
splashes over them,

they'll feed at last,
extracting all their nutrients

in just an hour or two
in the whole day.

Like all intertidal animals,
barnacles have to deal with

fluctuating conditions on both
a daily and seasonal basis.

However recent research suggests
that barnacles and other

creatures have to cope with changes
over a much bigger timescale.

Changes that we may be
responsible for.

Nova Mieskowska
of the Marine Biological Association

has been analysing long-term data
on barnacles here in Devon.

Well, if you don't know barnacles
very well, it has to be said that

they do all look rather alike but
when you do know barnacles well,

like you, you know that there are
subtle differences between species

and that those species' differences
are connected to climate change.

Is that right?

Yes, we've found over the many
decades that we've been studying

barnacles all around the UK but
especially down in the South West

here that the warm water barnacles,
which you can see here

with the slightly more
greenish tinges, they're kite shaped.

These warm water barnacles have
become a lot more abundant,

especially over the last 20, 25 years

since climate change really
started to take hold.

Their northern limits are in Scotland
for warm water barnacles

and they go and they
go all the way down south

past the Mediterranean and slightly
into north Africa,

whereas the cold water barnacles
these are the ones

that are slightly whiter.

This is the one Semibalanus
balanoides here.

I can see it now. You have to
get your eye in, don't you.

Their northern limits go way
up into the Arctic Circle,

but their southern limits have been
cut back and back, further north.

They used to be in northern Spain
in the Bay of Biscay,

where there has
been a big trimming northwards

because it's plainly too warm
for them to live there anymore.

We're even seeing
the effects here in the South West.

We've seen a massive decline
in the survival

of these cold water barnacles.

Do they get bigger than this
or is this their usual size?

This is quite a representative
size, however

when you find shores further up
north with just the cold water

species, Semibalanus balanoides
can grow quite large.

In its first six months, it can grow
significantly bigger than

the warm water ones do.

So given an opportunity, it can
increase its size quite rapidly.

And have they got their natural
predators dotted around the surface?

Yes, you can see we've got some
marauding dog whelks

and these dog whelks do
preferentially eat the cold water
barnacles

Semibalanus balanoides, so it will be
very interesting to see whether,

when we lose these for good
in the South West,

whether the dog whelks will be
able to change

and feed entirely
on the warm water barnacle or not.

Well, I guess the story of evolution
is often change or die.

Yes.

It is alarming to think that
we might be responsible

for affecting the survival of the
creatures we know and love so well.

However because they have adapted to
one of the toughest places on Earth,

rock pool animals have outlived many
other species they shared

the seas with, including
my favourites, the trilobites.

As a palaeontologist,
I marvel to think that their

ancestors lived alongside fossil
species I have studied

but whose lives
I can only really imagine.

And rock pool animals may well
outlive us.

For if anything has got what it
takes to endure, it is them,

for they are masters of
an ever-changing environment.

And if we look around, we can
see that they have played

an important part in our own
evolution.

Here on Oronsay in the Western Isles
of Scotland,

the whole hill behind me
is a shell midden.

Our ancestors 7,000 years ago
or more collected huge numbers

of limpets and some cockles that
became a staple part of their diet.

This shows what an extraordinary
asset the intertidal zone

has been in the course
of human evolution.

So maybe it is our hunter-gatherer
past that leaves us

with such a basic
curiosity about rock pools.

Now we number in our billions,
we are probably the biggest threat

to the seashore,
but, as we have seen, the creatures

of the rock pool have what it takes
to survive well into the future.

On my journey, I have had just
a brief glimpse into the world

of rock pools but have discovered
first-hand the marvels they hold.

Throughout hundreds
of millions of years,

they have evolved extraordinary
adaptations to survive

one of the toughest
environments on Earth.

They have also played a part in our
own colonisation of the planet.

May they continue to be a source
of joy and wonder to us all.

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