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{\an8}Our shallow seas cover 10% of the ocean.
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A tapestry of coral reefs,
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sandy flats and seagrass meadows,
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long thought to be silent worlds.
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But in recent times,
new underwater microphones have revealed
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that these waters are alive
with extraordinary noises.
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A treasure trove of sounds
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that is changing our understanding
of life beneath the waves.
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And perhaps the strangest sound
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can be heard
off Australia's Great Barrier Reef.
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The largest reef on the planet.
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Here, each winter,
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mysterious noises come out of the blue.
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Once thought to be
the sonar of submarines...
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we've recently learned
that the truth is even stranger.
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For this is the song
of the dwarf minke whale.
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They spend most of their lives alone,
way out in the open ocean.
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But for just a few weeks each year,
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they travel to the ribbon reefs
off the northern edge of Queensland.
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It's thought
that whales use the coral reef
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as a kind of amphitheater
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to broadcast their otherworldly calls,
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named by scientists
as the Star Wars vocalization.
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It's created by pumping air
between their throat
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and their thousand-liter lungs,
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producing two harmonies simultaneously.
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A high melody.
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And some deep base.
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In shallow water,
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sound travels five times faster
than in air.
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So, when they call,
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it soon attracts the attention of others.
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Incredibly,
this is the only place in the world
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where these whales come together
and sing like this.
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It could be a chance for males to show off
to each other,
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or perhaps impress the females.
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Since scientists realized
that it was whales
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producing these alien-like calls,
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we've discovered a whole new world
of sound in the shallow seas.
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And the noisiest place of all...
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is on the reef itself.
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Here, creatures click, pop, and honk
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to defend territories and attract mates.
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Only passing predators, like reef sharks,
temporarily silence things.
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Low booms, recorded for the first time,
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are thought to be love songs
of grouper fish.
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And schooling jacks don't just hear noise,
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they feel it too,
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using vibrations to stay in formation.
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Healthy reefs are so loud,
they can be detected from ten miles away.
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In this coral cacophony,
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making yourself heard
is a constant challenge.
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So, one little fish has recently started
to make a brand-new sound.
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The Ambon damselfish.
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Just four inches long,
they are the Romeos of the reef.
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Males spend much of their time
sprucing up their bachelor pads
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in a bid to impress the females.
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For this young male,
cleaning up is a bit of a struggle.
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But when everything's just right,
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it's time to find a date.
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On such a busy reef,
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there can be hundreds of species
clicking and popping.
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So, damselfish do something different.
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They sing.
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We can only tune in
to their delicate warbles
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using specialist microphones.
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Most remarkably,
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this was heard for the first time
just eight years ago.
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Scientists believe that
one male began to sing this short melody
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and then other males copied him...
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making it perhaps
nature's newest love song.
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This underwater ballad
soon attracts a female's attention.
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Clearly a singing fish is quite a catch.
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Across the planet,
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noisy coral reefs make up less than 10%
of the shallow seas.
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Most of the seafloor
is expansive sand flats.
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In the quiet waters of the Bahamas,
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we're now learning that animals use sound
in evermore sophisticated ways.
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Perhaps none more so
than the Atlantic spotted dolphin.
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For these intelligent creatures,
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the greatest challenge
in this seemingly barren land
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is finding fish to eat.
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But we now know that they do this
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using an astonishing sonic superpower.
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Like all dolphins,
they hunt using echolocation.
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But in shallow waters,
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instead of using this skill
to find food in front of them,
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they use it to search for fish
completely hidden from sight.
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By forcing air
around their nasal passages,
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they create high intensity clicks,
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which are so powerful
that they penetrate through the sand,
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bouncing off objects beneath.
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This allows Atlantic spotted dolphins
to scan the seafloor like metal detectors.
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When prey is detected,
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they ramp their clicks up
to over 400 per second.
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Known as "the buzz,"
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it's so forceful
that it can stun the fish,
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making them easier to catch...
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as long as you don't let go.
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Success at last.
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The dolphins' clicks make them the masters
of acoustic hunting in the shallow seas.
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But on other tropical sandbanks
in Southeast Asia...
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one little fish also uses clicks,
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but for a very different purpose.
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Saddleback clown fish.
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Small fish with big attitudes.
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This raucous group of around a dozen
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has set up home on a sea anemone
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the size of a dinner plate.
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Unlike their cousins on the reef,
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these fish have almost nowhere
to hide from danger.
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So, the colony relies on sound.
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The smaller fish spend their days
playing rowdy games of chase.
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They're ruled over by the only female.
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The biggest and loudest fish.
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By knocking her teeth together,
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she produces powerful clicks
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to keep the colony in order.
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Because she needs them to work with her
to protect her precious offspring.
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Hundreds of little clown fish eggs,
each just the size of a grain of rice.
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The largest male softly calls to them,
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a behavior that has
never been recorded before.
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Incredibly, scientists believe
that the baby fish
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may sense this sound
inside their egg sacs.
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So, when they hatch,
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they can already recognize the calls
of their own species.
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Less than 1% will make it to adulthood
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because they're the perfect sized snack
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for hungry predators
who lurk beneath the sand.
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A swimming crab.
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An aggressive hunter
with a particular taste for fish eggs.
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With the intruder spotted,
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the clown fish alarm call
to alert the colony to the threat.
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And the female begins an acoustic attack.
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Her loud pops,
a warning to leave the eggs alone.
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Combined, the clown fish form a noisy mob.
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Finally, the biggest male gets physical,
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pushing with all his might.
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And the crab is sent scuttling.
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By using their voices,
and a little brute force,
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these feisty clown fish work together
to protect the next generation.
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But in shallow waters,
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it's not just animals
that make unusual noises.
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Off the coast of Florida...
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plants make sounds too.
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Here, vast seagrass meadows
turn the ocean an emerald green.
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As sunlight penetrates the water,
they start to fizz.
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Seagrasses use light and carbon dioxide
to make their food,
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and in doing so
produce tiny bubbles of oxygen.
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Slowed down over a hundred times...
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each one creates the
faintest whooshing sound
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as it peels away from the leaf.
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Billions of these bubbles bursting free...
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build to a sizzling soundscape.
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These meadows absorb carbon dioxide
35 times faster than the rain forest
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and produce so much oxygen,
these shallow seas are vital
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in the battle against climate change.
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For one precious gentle giant,
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the sound of fizzing vegetation
must be like a dinner bell.
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The West Indian manatee.
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A distant relative of the elephant,
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there are less than 7000 individuals
left in the wild.
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From an animal that weighs half a ton,
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you might expect to hear
great grunts or bellows.
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But in fact,
manatees make a surprising sound.
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It might not sound like much,
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but new research shows that these
high-pitched squeaks
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travel up to 800 feet
in quiet, shallow waters.
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For mothers and calves,
this is crucial for keeping together.
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Each winter, temperatures out at sea
plummet so low,
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the little ones can perish in the cold.
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So, they must travel six miles inland,
through rivers,
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to reach the safety of warm water springs.
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An annual manatee migration.
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When the playful calf wanders off...
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Mum calls her back in line.
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The pair constantly chatter
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so they can stick together
on their journey.
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But in recent times,
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the soundscape
of the manatees' ancient migration route
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has started to change.
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The human population in Florida
has increased dramatically.
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There are now a hundred and thirty
vessels for every manatee.
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In shallow waters,
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propeller sounds
can disorientate the manatees,
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drowning out their soft squeaks...
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making it harder for mums and calves
to keep in touch.
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It takes two days of swimming
before the sound of boats starts to fade.
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And in the distance,
there are some familiar chirps.
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This mum and calf
aren't the only ones to have made it.
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Manatees from far and wide have traveled
from the dangerously cold ocean
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to this warm spring.
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By using squeaks to keep in touch...
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these threatened mammals can make it
to this lifesaving refuge.
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It's just one of the many new discoveries
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that are changing our understanding
of the importance of sound
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in these so-called silent waters.
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To capture the soundscape
of the coral reef
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in more detail than ever before,
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the Earthsounds team
traveled to Raja Ampat
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in the heart of Southeast Asia.
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The underwater world is famously called
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the Silent World by Jacques Cousteau,
but it's really far from it.
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{\an8}There's all sorts of popping and clicks
and almost whistles that you hear.
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So, there's a real cacophony of sounds
down there.
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With the reef so busy,
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working out exactly who is calling
can be tricky.
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So, the team enlisted the help
of marine biologist, Isla Hely.
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{\an8}On tropical reefs, fish chat
to each other for a myriad of reasons.
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We've known this for a long time,
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but we've been limited by the technologies
that we have to capture that sound.
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Isla hopes to be able to
decipher some of this reef chatter
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using a sound recording device
built specially for the series.
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So, this is our diver-operated
recording apparatus.
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We like to call her DORA.
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So, there's the microphone on top,
which is a hydrophone,
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but then you also have a camera
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so you can match what's making the noise
with the visuals.
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DORA enables Isla
to record the sound of the entire reef
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or point and focus on individual species.
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And with its removable head,
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Isla can suspend the hydrophone
away from her,
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allowing her to capture
close proximity recordings
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of reef residents who like to hide away.
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We've collected a whole cohort of sounds.
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There's some base-y, low frequency,
boing-y sounds
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and we believe those to be grouper.
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We have the quite sweet
weeping sound of the Ambon damselfish.
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But there have been some bizarre sounds
that we've been picking up.
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There could be a cryptic species
that's just hidden in a cave
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that we just haven't been able to see.
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Armed with DORA,
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Isla has been able to capture
individual fish conversations.
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And uncover sounds
that have never been recorded before.
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But whilst reefs here may be thriving
and full of sound,
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that isn't the case across the world.
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Warming oceans mean
90% of live coral reefs
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are expected to disappear by 2050.
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I'm increasingly seeing
more and more degraded reefs
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due to climate change.
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And when you listen,
it's quite haunting actually
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because all that sound
that creates the cacophony of the reef
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is missing.
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But a silent reef
isn't necessarily a dead one.
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Isla hopes that sound
could hold the key to conserving them.
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Recent research has shown
that when you play back sounds
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of healthy reefs within a degraded reef,
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you can actually bring in both fish larvae
and coral larvae,
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00:26:46,773 --> 00:26:51,028
and all the settlers that would help
to restore these ecosystems,
250
00:26:51,612 --> 00:26:54,323
potentially to the beautiful reefs
that they once were.
251
00:26:58,202 --> 00:27:00,621
Through new scientific breakthroughs,
252
00:27:01,288 --> 00:27:05,209
we're only just uncovering
how crucial sound is
253
00:27:05,209 --> 00:27:06,752
in these shallow seas.
254
00:27:09,046 --> 00:27:13,759
And just how noisy
healthy reefs really are.
255
00:27:14,718 --> 00:27:18,055
Every recording is a joy to listen to.
256
00:27:18,055 --> 00:27:20,557
And this is what reefs should be like
around the world.