The Blue Planet (2001): Season 1, Episode 7 - Tidal Seas - full transcript
Tidal marshes are one of the most productive parts of the world. Numerous plants support numerous animals, yet life is not easy: predators are attracted to these enormous quantities of food, forcing animals to seek constant protection from attack.
There is a force sufficiently powerful
to move the oceans of this world
It is a force, not of this earth
The moon is large enough
to generate gravity
and with sufficient force
to pull on the earth,
two hundred and thirty
thousand miles away
As the moon orbits the earth its gravity
sweeps across the face of our planet
Its power drags a great bulge of oceanic
water in its wake
- the rising tide
The River Amazon in Brazil
On some special days the
gravitational forces
of the moon and the sun pull together
- to extraordinary effect
A growing tidal wave from the ocean
is being forced two hundred miles inland
This is a tidal bore
Fortunately tidal bores are rare,
but the moon does create strong
tides out in the world's oceans,
on every day of the year
The Bay of Fundy, in Nova Scotia
The tides here are
the largest in the world
and have a profound effect on marine life,
creating a rich feeding ground
A feast that attracts some of the
largest diners on the planet
Humpback whales
But they are not the biggest
threat to the herring
These are finback whales
At seventy tonnes - the second
largest animal on earth,
but so beautifully streamlined that
it is the fastest of the great whales
This combination of
speed and immense size
makes the finback a voracious
hunter of schooling fish
The Bay of Fundy can attract so many fish,
that during the summer,
as many as five hundred of these
magnificent whales hunt here every day
The feeding is best where
the tides run strongly
So the whales move
further into the bay,
following tidal rips
and searching for fish
Their movements are closely watched
by flocks of Cory Shearwaters
As the whales dive down
toward the fish
- more and more birds gather,
anxious to pick up scraps
The flowing tide may provide
a feast for the whales,
but before long it will turn
In just six hours,
one hundred billion tonnes of water
will flow out of the bay
The sea level falling
by as much as 15 metres
and exposing vast tracts
of mud... and sand
At first sight a barren place,
entirely devoid of life
In fact, the damp sand is
packed with microscopic life
- the meiofauna,
feeding in a sandy underworld,
quite unaffected by
the departure of the sea
But life is not all roses
in this miniature world
A sand bubbler crab - in Northern
Australia - it hunts meiofauna
Just a centimetre across, the sand
bubbler works at breakneck speed,
passing sand grains
into its mouth,
filtering out all the meiofauna
and kicking aside the waste
The crab will clean every grain of
sand within a metre of its burrow
Endless practise for the best back
heel in the Natural World
The crabs work fast because they can
only sieve when the sand is damp
Remarkably, they work the entire
surface of the beach
within just a couple of hours
of the tide retreating
Then they simply return to their
burrows and await the next tide
Underwater a falling tide is the
cue for some bizarre activity
These slow moving clams
use their muscular feet
to bury themselves under the sand
If they fail to get under cover,
the tide will leave them exposed
to the air and they will perish
But once underground they can
wait deep down in the sand,
safe beneath the beach
And not a moment too soon
June in Southeast Alaska
and in just four hours
a vast sandy beach is exposed
by the falling tide
The bears are hungry
- at this time of year
the pickings on land
are few and far between
But any food here has long since
buried itself deep under the sand
To a hungry adult bear
that is no barrier
- they smell the clams through
the sand and simply dig them out
For such large animals,
they show quite extraordinary dexterity
at opening the unfortunate
shellfish
Cubs try their luck, too,
none too successfully!
But for the adults the shellfish feast
lasts as long as the tide remains out
Table Mountain in South Africa
Every day the retreating waves leave
flotsam somewhere on the beach...
...and this creature is scenting the
currents for the odour of rotting fish
The tide carries the scent
far into the surf zone
Responding to the smell,
snails emerge from the sand
This is a race against the tide
- the snails need to find their meal
before the tide leaves it
beyond their reach
But snails are slow and
the tides fall rapidly
These, however,
are no ordinary snails
They can surf!
They ride the waves up
the beach but all too soon
the tide leaves the fish
beyond the surf zone
Without the sea there's a danger
that the snails will lose the scent,
but as long as the sand remains damp they
can still follow a faint trail to the food
Once there they tuck in
with macabre relish
Good things come to
those who wait!
Before long the heat
of the sun forces them
to retreat into the sand to
await the return of the next tide
February in Britain
The falling tide is eagerly
awaited by these knot
As the water retreats
countless small invertebrates
are seeking shelter under the mud
And with good reason
Waders are specialists
at probing in the mud,
their wide variety of beak
shapes designed
for reaching different
invertebrate dinners
Keys that unlock the safety
of the tidal flats
But within a few hours
the tide will turn again
Soon the waders are out
of their depth
and the creatures of the mud
are safe once more
Underwater incoming tides
can create a strong current
And flounder are experts
at hitching a tidal lift
They are shaped rather like a kite
- a perfect design for gliding on the tide
In Newfoundland on the
East Coast of Canada,
large numbers of flounder ride
the currents up into the shallows
They have come to hunt invertebrates that
will emerge now that the water is back
The pickings in the shallows
can be very good
The activity has
not gone unnoticed
But Ospreys can't dive deeply
As long as the water is more than a meter
deep, the found then will be safe
Going too far inshore
can be a risky business
This fish buries itself completely
in the sand at any sign of danger
But when the tide floods in again,
as long as the coast is clear
- these sand lancet will re-emerge
After a wait of six hours under the sand,
they are desperate for food and,
unlike flounder,
they head out to sea
They are looking for
shallow open water,
where the tidal currents will
concentrate their food - plankton
In their untold thousand they stream
toward the best feeding grounds
Where they simply pick up
tiny planktonic creatures from the water
But, if they swim too far off-shore
in search of food,
they risk running into large predators
that live out in deeper water
Dogfish - small sharks
The sand lancet have strayed out
of their safe depth
The effect of the turning tide can
be totally different on a rocky shore
Here on the coast of Vancouver Island
in Canada the sun bakes the exposed rock
It's virtually impossible to dig
underground when the sea retreats,
so these mussels and barnacles are
fully exposed to the heat of the sun
- literally cooking
in their own shells
And the seaweed simply dry to a crisp
It can be a wait of many hours
before the water returns
Throughout each month the size
and strength of the tide changes
The biggest tides of all happen
when the gravities of the
sun and moon pull in unison
That happens immediately
after the new moon...
...and again after the full moon
These are called the spring tides
They reveal vast tracts of sea bed
that would normally be covered
For these racoons it's a chance
to look for a seafood feast
A mother ventures forth with her kits
With the spring tide, they've
come further down the beach
than smaller tides would normally allow
Searching with their
extraordinarily sensitive paws
- they look for suitable prey
With the extreme low tide they
could find something special
And what could be better
than a red rock crab
That is, if it weren't for the risk
of a painful pinch
With large crabs
there's no substitute for experience
- the mother makes an expert's catch
But the kits learn fast!
And for those that don't
- begging is always worth a try!
All too soon the returning tide
will cover the racoon's table
For all the invertebrates
it is a welcome relief,
but in rough weather they are
exposed to the worst of the waves
Even when there are no waves
- the incoming tide
can create considerable forces underwater
The gaps between these small islands on
the East coast of Vancouver
Island channel the tidal flow
As the tide keeps rising,
gradually the water flows
faster and soon these giant thirty metre
long bull kelp plants bend to the current
They are sufficiently flexible
to cope without too much damage,
but there are some spots where
the currents are especially powerful
This is the Nakwakto Rapids
At the turn of the tide,
water from almost seven hundred miles
of coastal fjords will have
to empty through a gap
of less than half a mile wide
Within a few minutes the current
is already picking up speed,
until water roars by at over
seventeen miles per hour
Tidal currents are not always
a damaging force
- here in the Poor Knight
Islands of New Zealand,
weak tides run through rock arches,
making an ideal resting
place for stingrays
These rays congregate here
in huge numbers every March
- they've come to breed
The arches funnel the current,
which the rays can ride
with a minimum of effort,
so saving energy
Nearby, out in open water,
a school of two spotted desmoiselle fish
are feeding on plankton
and the current
is perfect for sweeping
their food past them
Once the current starts to weaken,
there is insufficient food to
warrant the risks of swimming
about out here in the open
So the desmoiselles head off
to find shelter en-masse
Safety is in numbers
More and more desmoiselles pour
towards the cave entrances
that riddle the Poor
Knight's islands
Safe at last - inside the cave
they are far less exposed
to attack from predators
Thousands of desmoiselles and blue mao mao
wait for the return of the current,
when once again they will
head out into the open to feed
The moon's gravitational pull
is weaker nearer to the earth's equator,
so the more equatorial the location,
the smaller the tides
And out here in the Caribbean Sea
the tidal movements are slight
Even so, they are sufficient to push
free swimming plankton in their path
These are thimble jellyfish
They swim towards the sunlight
and invisible boundaries
formed by the tidal motion
help to herd them together,
until they gather in immense swarms
They put the tropical
sunshine to good use
- their brown colour
comes from algae that
live inside the jellyfish's bodies
and photosynthesise energy from the sun
In open water they
are fairly safe,
but the tide is sweeping the whole
swarm gently towards the Bahamas,
where hungry mouths are waiting
Although the sea level
does not change much
- the tides are still pushing
an enormous volume of water
from the ocean through the
small gaps between the island cays
Underwater the tidal currents
race past soft corals
And on over the sandy
banks themselves...
It is an immense area of coral sand
that is only just submerged at high tide
This incoming tide is bringing
in a fresh supply of oceanic plankton
and razorfish gather at the best spots
to catch the pick of the microscopic feast
Although there is plenty here
for these small fish to eat,
gathering in one place makes it
easy for their predators to find them
A nurse shark is little threat
But this sound heralds
a quite different danger
A bottlenose dolphin
It's using its sonar to locate
razor fish beneath the sand
Once it finds a suitable target
it simply digs out its prey
The buried fish have no defence
against this attack
They will simply have to wait
and hope they aren't found out
This dolphin appears to have a razor
fish craving - well, she is pregnant
Success, at last
The incoming tide sweeps
on towards America,
flooding across vast flat
plains of seagrass
They are so shallow that,
at low tide,
all large fish are forced
to retreat into deep water channels
Like these nurse sharks...
and these stingrays
Both predators hunt crustaceans
on the seagrass beds,
but until the flooding tide brings
enough water for them to swim in,
they will have to wait
So for now this tulip
snail it appears safe
to patrol the shallows
in search of a meal
But is it?
This I s a rather
bigger kind of snail
At five kilogrammes in weight,
the giant horse conch
has little to fear from any shark...
and it has a taste for tulip snail
Sensing the approaching danger
- the snail flees
But in a world of snail paces
- the conch is something of a Ferrari
It calls for desperate measures
Exhausted by the effort
of its last ditch attempt,
the tulip snail is slowly gunned down
The tide still has to rise for another
hour before the big predators can feed
But out on the flats the scent of
dying snail wafts away on the tide
It's a scent that these hermit crabs
are particularly partial to
It's vital that the crabs have
the best possible protection
from the heavy teeth of
the waiting sharks and rays
For that they need the shell
with a perfect fit
Today there is new real
estate on offer
- and competition in this
housing market is fierce
The action becomes even
more desperate
when the shell of the devoured
snail is ready for release
This crab simply can't
wait any longer
But it's a decidedly
risky acquisition
The risk paid off handsomely
- the new shell is both lighter
and stronger than the old home
and it's not a moment too soon
because the tide is flowing in strongly,
flooding the plains
At last, the predators are free
to start their foraging
Both the stingrays and sharks have
a highly developed electrical sense
which they use to search
for buried invertebrates
- they can sense minute
movements beneath the sand
Finding a promising signal,
this ray digs out its meal,
an unprotected hermit crab
would have no chance
Within a few hours the tide
ebbs out once more,
and all the predators
are forced to leave
They will have to wait
until the next high tide
before making another feeding foray
At certain times of the
year called the equinox,
spring tides are exceptionally large
and rise even higher than normal
Now predators can reach the very
shallowest fringes of the seagrass flats
These two metre long tarpon
are heading further inshore still
They are heading for the mangroves
These flooded forests cover huge
areas of the coastal shallows
Extraordinarily, the roots
of the mangrove trees
can live in salt water and they
make a perfect nursery for small fish
Silversides and snapper find
sanctuary in the maze of roots
- big predators seldom
find a way in here
And now the tide is
falling once more
The water starts losing
what little oxygen it contained
and quickly becomes stagnant
Most predators have
abandoned the mangroves,
but these tarpon are still
here trapped by the falling tide
The dissolved oxygen
is fast running out,
but they have a vital
survival technique...
...they can breathe air
Pumped up with fresh oxygen
they can easily out
manoeuvre the dozy silversides
The tide has turned again
And this is no ordinary tide
Since it is the equinox
- the tide is rising fast
but now out to sea a hurricane is on
its way, forcing the tide yet higher
The passing storm leaves large areas
of the coast flooded by the sea...
...and the low lying islands
like the Bahamas
are even more prone
to storm flooding
The sun's power here is immense
As the tide recedes and the
remaining flood water evaporates
- a remarkable transformation
takes place...
The mud is coated with
a magical world of salt
Any remaining water is extremely salty
- very few creatures can survive here...
...except these brine shrimp
And on the water's edge, brine flies
Both are the favourite food
of an extraordinary animal
The Caribbean Flamingo
Remarkably, they actually
seek out such briny places
- they are the best spots for
them to find their food
And they also provide the protection
the flamingos need to raise their young
Nesting sites like this are
surrounded by corrosive brine
It's a formidable barrier to any predators
seeking to dine on flamingo chicks
The Flamingo takes the precaution
of building next
Just in case of further flatting
Strangely, it's actually the
power of the storm tides
that gives the flamingos
both their food
and a perfect habitat in which to breed
The breeding of many animals in the ocean
is closely co-ordinated
with the tidal cycles
A half moon in November.
It is the time for small tides.
Christmas Island in the Pacific
Strange happenings are afoot
It is one of only a few nights each year
when female Christmas Island crabs
risk heading down towards the sea
Around the island they number
in tens of thousands
and all of them are laden
with hundreds of eggs
They have to shed them into the ocean
if the eggs are to develop into baby crabs
But these are land crabs and they can
neither swim nor breathe underwater
There is a great risk of drowning,
which is why they pick the
smallest tides of the month
- to minimise the danger
The eggs will develop far
offshore and in exactly
one month's time a great swarm
of baby crabs will return,
again choosing the perfect tide
Whether it's the daily or monthly cycle,
tides are the rhythm of the ocean
- its pulsing clock
For every tide brings opportunity
to marine life somewhere in the world
Now a spring tide is flooding the
shallows and hunters are on the prowl
A small group of bottlenose dolphin
are working their way
inshore to start a quite
extraordinary hunting campaign
After one successful pass the dolphin
move off to start again
One animal peels off from the group
and swims rapidly in a circle,
stirring up the mud and driving
the mullet towards the other waiting dolphins
It's a remarkable team effort
and it is extremely effective
The dolphin will feed like this
for as long as the tide grants
them access to the shallows
Eventually the falling tide will
force the dolphin to leave the flats
and the mullet will be safe once more
- until the next high tide
Because in the ocean every
turn of the tide spells
the difference between
life and death, somewhere
to move the oceans of this world
It is a force, not of this earth
The moon is large enough
to generate gravity
and with sufficient force
to pull on the earth,
two hundred and thirty
thousand miles away
As the moon orbits the earth its gravity
sweeps across the face of our planet
Its power drags a great bulge of oceanic
water in its wake
- the rising tide
The River Amazon in Brazil
On some special days the
gravitational forces
of the moon and the sun pull together
- to extraordinary effect
A growing tidal wave from the ocean
is being forced two hundred miles inland
This is a tidal bore
Fortunately tidal bores are rare,
but the moon does create strong
tides out in the world's oceans,
on every day of the year
The Bay of Fundy, in Nova Scotia
The tides here are
the largest in the world
and have a profound effect on marine life,
creating a rich feeding ground
A feast that attracts some of the
largest diners on the planet
Humpback whales
But they are not the biggest
threat to the herring
These are finback whales
At seventy tonnes - the second
largest animal on earth,
but so beautifully streamlined that
it is the fastest of the great whales
This combination of
speed and immense size
makes the finback a voracious
hunter of schooling fish
The Bay of Fundy can attract so many fish,
that during the summer,
as many as five hundred of these
magnificent whales hunt here every day
The feeding is best where
the tides run strongly
So the whales move
further into the bay,
following tidal rips
and searching for fish
Their movements are closely watched
by flocks of Cory Shearwaters
As the whales dive down
toward the fish
- more and more birds gather,
anxious to pick up scraps
The flowing tide may provide
a feast for the whales,
but before long it will turn
In just six hours,
one hundred billion tonnes of water
will flow out of the bay
The sea level falling
by as much as 15 metres
and exposing vast tracts
of mud... and sand
At first sight a barren place,
entirely devoid of life
In fact, the damp sand is
packed with microscopic life
- the meiofauna,
feeding in a sandy underworld,
quite unaffected by
the departure of the sea
But life is not all roses
in this miniature world
A sand bubbler crab - in Northern
Australia - it hunts meiofauna
Just a centimetre across, the sand
bubbler works at breakneck speed,
passing sand grains
into its mouth,
filtering out all the meiofauna
and kicking aside the waste
The crab will clean every grain of
sand within a metre of its burrow
Endless practise for the best back
heel in the Natural World
The crabs work fast because they can
only sieve when the sand is damp
Remarkably, they work the entire
surface of the beach
within just a couple of hours
of the tide retreating
Then they simply return to their
burrows and await the next tide
Underwater a falling tide is the
cue for some bizarre activity
These slow moving clams
use their muscular feet
to bury themselves under the sand
If they fail to get under cover,
the tide will leave them exposed
to the air and they will perish
But once underground they can
wait deep down in the sand,
safe beneath the beach
And not a moment too soon
June in Southeast Alaska
and in just four hours
a vast sandy beach is exposed
by the falling tide
The bears are hungry
- at this time of year
the pickings on land
are few and far between
But any food here has long since
buried itself deep under the sand
To a hungry adult bear
that is no barrier
- they smell the clams through
the sand and simply dig them out
For such large animals,
they show quite extraordinary dexterity
at opening the unfortunate
shellfish
Cubs try their luck, too,
none too successfully!
But for the adults the shellfish feast
lasts as long as the tide remains out
Table Mountain in South Africa
Every day the retreating waves leave
flotsam somewhere on the beach...
...and this creature is scenting the
currents for the odour of rotting fish
The tide carries the scent
far into the surf zone
Responding to the smell,
snails emerge from the sand
This is a race against the tide
- the snails need to find their meal
before the tide leaves it
beyond their reach
But snails are slow and
the tides fall rapidly
These, however,
are no ordinary snails
They can surf!
They ride the waves up
the beach but all too soon
the tide leaves the fish
beyond the surf zone
Without the sea there's a danger
that the snails will lose the scent,
but as long as the sand remains damp they
can still follow a faint trail to the food
Once there they tuck in
with macabre relish
Good things come to
those who wait!
Before long the heat
of the sun forces them
to retreat into the sand to
await the return of the next tide
February in Britain
The falling tide is eagerly
awaited by these knot
As the water retreats
countless small invertebrates
are seeking shelter under the mud
And with good reason
Waders are specialists
at probing in the mud,
their wide variety of beak
shapes designed
for reaching different
invertebrate dinners
Keys that unlock the safety
of the tidal flats
But within a few hours
the tide will turn again
Soon the waders are out
of their depth
and the creatures of the mud
are safe once more
Underwater incoming tides
can create a strong current
And flounder are experts
at hitching a tidal lift
They are shaped rather like a kite
- a perfect design for gliding on the tide
In Newfoundland on the
East Coast of Canada,
large numbers of flounder ride
the currents up into the shallows
They have come to hunt invertebrates that
will emerge now that the water is back
The pickings in the shallows
can be very good
The activity has
not gone unnoticed
But Ospreys can't dive deeply
As long as the water is more than a meter
deep, the found then will be safe
Going too far inshore
can be a risky business
This fish buries itself completely
in the sand at any sign of danger
But when the tide floods in again,
as long as the coast is clear
- these sand lancet will re-emerge
After a wait of six hours under the sand,
they are desperate for food and,
unlike flounder,
they head out to sea
They are looking for
shallow open water,
where the tidal currents will
concentrate their food - plankton
In their untold thousand they stream
toward the best feeding grounds
Where they simply pick up
tiny planktonic creatures from the water
But, if they swim too far off-shore
in search of food,
they risk running into large predators
that live out in deeper water
Dogfish - small sharks
The sand lancet have strayed out
of their safe depth
The effect of the turning tide can
be totally different on a rocky shore
Here on the coast of Vancouver Island
in Canada the sun bakes the exposed rock
It's virtually impossible to dig
underground when the sea retreats,
so these mussels and barnacles are
fully exposed to the heat of the sun
- literally cooking
in their own shells
And the seaweed simply dry to a crisp
It can be a wait of many hours
before the water returns
Throughout each month the size
and strength of the tide changes
The biggest tides of all happen
when the gravities of the
sun and moon pull in unison
That happens immediately
after the new moon...
...and again after the full moon
These are called the spring tides
They reveal vast tracts of sea bed
that would normally be covered
For these racoons it's a chance
to look for a seafood feast
A mother ventures forth with her kits
With the spring tide, they've
come further down the beach
than smaller tides would normally allow
Searching with their
extraordinarily sensitive paws
- they look for suitable prey
With the extreme low tide they
could find something special
And what could be better
than a red rock crab
That is, if it weren't for the risk
of a painful pinch
With large crabs
there's no substitute for experience
- the mother makes an expert's catch
But the kits learn fast!
And for those that don't
- begging is always worth a try!
All too soon the returning tide
will cover the racoon's table
For all the invertebrates
it is a welcome relief,
but in rough weather they are
exposed to the worst of the waves
Even when there are no waves
- the incoming tide
can create considerable forces underwater
The gaps between these small islands on
the East coast of Vancouver
Island channel the tidal flow
As the tide keeps rising,
gradually the water flows
faster and soon these giant thirty metre
long bull kelp plants bend to the current
They are sufficiently flexible
to cope without too much damage,
but there are some spots where
the currents are especially powerful
This is the Nakwakto Rapids
At the turn of the tide,
water from almost seven hundred miles
of coastal fjords will have
to empty through a gap
of less than half a mile wide
Within a few minutes the current
is already picking up speed,
until water roars by at over
seventeen miles per hour
Tidal currents are not always
a damaging force
- here in the Poor Knight
Islands of New Zealand,
weak tides run through rock arches,
making an ideal resting
place for stingrays
These rays congregate here
in huge numbers every March
- they've come to breed
The arches funnel the current,
which the rays can ride
with a minimum of effort,
so saving energy
Nearby, out in open water,
a school of two spotted desmoiselle fish
are feeding on plankton
and the current
is perfect for sweeping
their food past them
Once the current starts to weaken,
there is insufficient food to
warrant the risks of swimming
about out here in the open
So the desmoiselles head off
to find shelter en-masse
Safety is in numbers
More and more desmoiselles pour
towards the cave entrances
that riddle the Poor
Knight's islands
Safe at last - inside the cave
they are far less exposed
to attack from predators
Thousands of desmoiselles and blue mao mao
wait for the return of the current,
when once again they will
head out into the open to feed
The moon's gravitational pull
is weaker nearer to the earth's equator,
so the more equatorial the location,
the smaller the tides
And out here in the Caribbean Sea
the tidal movements are slight
Even so, they are sufficient to push
free swimming plankton in their path
These are thimble jellyfish
They swim towards the sunlight
and invisible boundaries
formed by the tidal motion
help to herd them together,
until they gather in immense swarms
They put the tropical
sunshine to good use
- their brown colour
comes from algae that
live inside the jellyfish's bodies
and photosynthesise energy from the sun
In open water they
are fairly safe,
but the tide is sweeping the whole
swarm gently towards the Bahamas,
where hungry mouths are waiting
Although the sea level
does not change much
- the tides are still pushing
an enormous volume of water
from the ocean through the
small gaps between the island cays
Underwater the tidal currents
race past soft corals
And on over the sandy
banks themselves...
It is an immense area of coral sand
that is only just submerged at high tide
This incoming tide is bringing
in a fresh supply of oceanic plankton
and razorfish gather at the best spots
to catch the pick of the microscopic feast
Although there is plenty here
for these small fish to eat,
gathering in one place makes it
easy for their predators to find them
A nurse shark is little threat
But this sound heralds
a quite different danger
A bottlenose dolphin
It's using its sonar to locate
razor fish beneath the sand
Once it finds a suitable target
it simply digs out its prey
The buried fish have no defence
against this attack
They will simply have to wait
and hope they aren't found out
This dolphin appears to have a razor
fish craving - well, she is pregnant
Success, at last
The incoming tide sweeps
on towards America,
flooding across vast flat
plains of seagrass
They are so shallow that,
at low tide,
all large fish are forced
to retreat into deep water channels
Like these nurse sharks...
and these stingrays
Both predators hunt crustaceans
on the seagrass beds,
but until the flooding tide brings
enough water for them to swim in,
they will have to wait
So for now this tulip
snail it appears safe
to patrol the shallows
in search of a meal
But is it?
This I s a rather
bigger kind of snail
At five kilogrammes in weight,
the giant horse conch
has little to fear from any shark...
and it has a taste for tulip snail
Sensing the approaching danger
- the snail flees
But in a world of snail paces
- the conch is something of a Ferrari
It calls for desperate measures
Exhausted by the effort
of its last ditch attempt,
the tulip snail is slowly gunned down
The tide still has to rise for another
hour before the big predators can feed
But out on the flats the scent of
dying snail wafts away on the tide
It's a scent that these hermit crabs
are particularly partial to
It's vital that the crabs have
the best possible protection
from the heavy teeth of
the waiting sharks and rays
For that they need the shell
with a perfect fit
Today there is new real
estate on offer
- and competition in this
housing market is fierce
The action becomes even
more desperate
when the shell of the devoured
snail is ready for release
This crab simply can't
wait any longer
But it's a decidedly
risky acquisition
The risk paid off handsomely
- the new shell is both lighter
and stronger than the old home
and it's not a moment too soon
because the tide is flowing in strongly,
flooding the plains
At last, the predators are free
to start their foraging
Both the stingrays and sharks have
a highly developed electrical sense
which they use to search
for buried invertebrates
- they can sense minute
movements beneath the sand
Finding a promising signal,
this ray digs out its meal,
an unprotected hermit crab
would have no chance
Within a few hours the tide
ebbs out once more,
and all the predators
are forced to leave
They will have to wait
until the next high tide
before making another feeding foray
At certain times of the
year called the equinox,
spring tides are exceptionally large
and rise even higher than normal
Now predators can reach the very
shallowest fringes of the seagrass flats
These two metre long tarpon
are heading further inshore still
They are heading for the mangroves
These flooded forests cover huge
areas of the coastal shallows
Extraordinarily, the roots
of the mangrove trees
can live in salt water and they
make a perfect nursery for small fish
Silversides and snapper find
sanctuary in the maze of roots
- big predators seldom
find a way in here
And now the tide is
falling once more
The water starts losing
what little oxygen it contained
and quickly becomes stagnant
Most predators have
abandoned the mangroves,
but these tarpon are still
here trapped by the falling tide
The dissolved oxygen
is fast running out,
but they have a vital
survival technique...
...they can breathe air
Pumped up with fresh oxygen
they can easily out
manoeuvre the dozy silversides
The tide has turned again
And this is no ordinary tide
Since it is the equinox
- the tide is rising fast
but now out to sea a hurricane is on
its way, forcing the tide yet higher
The passing storm leaves large areas
of the coast flooded by the sea...
...and the low lying islands
like the Bahamas
are even more prone
to storm flooding
The sun's power here is immense
As the tide recedes and the
remaining flood water evaporates
- a remarkable transformation
takes place...
The mud is coated with
a magical world of salt
Any remaining water is extremely salty
- very few creatures can survive here...
...except these brine shrimp
And on the water's edge, brine flies
Both are the favourite food
of an extraordinary animal
The Caribbean Flamingo
Remarkably, they actually
seek out such briny places
- they are the best spots for
them to find their food
And they also provide the protection
the flamingos need to raise their young
Nesting sites like this are
surrounded by corrosive brine
It's a formidable barrier to any predators
seeking to dine on flamingo chicks
The Flamingo takes the precaution
of building next
Just in case of further flatting
Strangely, it's actually the
power of the storm tides
that gives the flamingos
both their food
and a perfect habitat in which to breed
The breeding of many animals in the ocean
is closely co-ordinated
with the tidal cycles
A half moon in November.
It is the time for small tides.
Christmas Island in the Pacific
Strange happenings are afoot
It is one of only a few nights each year
when female Christmas Island crabs
risk heading down towards the sea
Around the island they number
in tens of thousands
and all of them are laden
with hundreds of eggs
They have to shed them into the ocean
if the eggs are to develop into baby crabs
But these are land crabs and they can
neither swim nor breathe underwater
There is a great risk of drowning,
which is why they pick the
smallest tides of the month
- to minimise the danger
The eggs will develop far
offshore and in exactly
one month's time a great swarm
of baby crabs will return,
again choosing the perfect tide
Whether it's the daily or monthly cycle,
tides are the rhythm of the ocean
- its pulsing clock
For every tide brings opportunity
to marine life somewhere in the world
Now a spring tide is flooding the
shallows and hunters are on the prowl
A small group of bottlenose dolphin
are working their way
inshore to start a quite
extraordinary hunting campaign
After one successful pass the dolphin
move off to start again
One animal peels off from the group
and swims rapidly in a circle,
stirring up the mud and driving
the mullet towards the other waiting dolphins
It's a remarkable team effort
and it is extremely effective
The dolphin will feed like this
for as long as the tide grants
them access to the shallows
Eventually the falling tide will
force the dolphin to leave the flats
and the mullet will be safe once more
- until the next high tide
Because in the ocean every
turn of the tide spells
the difference between
life and death, somewhere