0:01:25 > 0:01:30Most of the earth is covered by water.
0:01:30 > 0:01:33In fact, two-thirds of it is.
0:01:33 > 0:01:36And it's only in this generation
0:01:36 > 0:01:42that we have been able to move about it with any degree of freedom
0:01:42 > 0:01:45as I am doing now.
0:01:45 > 0:01:52So perhaps it's not surprising that still most of this vast domain
0:01:52 > 0:01:54is still unexplored.
0:01:56 > 0:02:00And in the geographical sense,
0:02:00 > 0:02:05the surface of the sea, the floor of the sea,
0:02:05 > 0:02:08is even more varied than the surface of the land.
0:02:24 > 0:02:27To see just how varied it is,
0:02:27 > 0:02:30let's take an imaginary journey across the Pacific
0:02:30 > 0:02:33starting in the west, where the ocean is deeper
0:02:33 > 0:02:36than anywhere else on the globe - The Mariana trench.
0:02:36 > 0:02:40The bottom of this immense valley seven miles below the surface
0:02:40 > 0:02:43is grooved by deep faults.
0:02:43 > 0:02:46If Mount Everest rose from the bottom here,
0:02:46 > 0:02:50its summit would still be beneath 7,000 feet of water.
0:02:50 > 0:02:53Down at the very bottom, the water pressure
0:02:53 > 0:02:56is some seven tons per square inch,
0:02:56 > 0:02:59the temperature is close to freezing, and it's pitch dark,
0:02:59 > 0:03:01for it's far, far beyond the reach of sunlight.
0:03:15 > 0:03:18As we climb up out of the trench,
0:03:18 > 0:03:21we move onto a plain covered with reddish mud.
0:03:27 > 0:03:29A few hills rise from it,
0:03:29 > 0:03:33but there are still some 20,000 feet of water above us.
0:03:35 > 0:03:38Travel eastwards over these plains for 1,000 miles,
0:03:38 > 0:03:41and we reach a range of fantastic mountains.
0:03:41 > 0:03:44Their summits are covered by a white deposit like snow,
0:03:44 > 0:03:48composed of the limestone skeletons of microscopic organisms
0:03:48 > 0:03:51that have drifted down from the surface waters.
0:03:51 > 0:03:53They never reach the lower slopes,
0:03:53 > 0:03:56for the water pressure becomes so great they dissolve.
0:03:58 > 0:04:01Currents sweeping up from the south
0:04:01 > 0:04:04pile the sand into dunes 150 feet high
0:04:04 > 0:04:07which advance slowly across the sea floor
0:04:07 > 0:04:09as dunes do in a desert on land.
0:04:14 > 0:04:17In places, the sand is littered with metallic lumps,
0:04:17 > 0:04:22some as big as cannon balls - manganese that under these pressures
0:04:22 > 0:04:24has precipitated out from the salty water.
0:04:34 > 0:04:38After a journey of 4,000 miles,
0:04:38 > 0:04:40we reach the biggest mountains of all.
0:04:40 > 0:04:44These are the flanks of the great volcanic islands of Hawaii.
0:04:44 > 0:04:47Their sides are far steeper than any mountain on land,
0:04:47 > 0:04:51for they are never eroded by frost or by rivers armed with gravel.
0:04:51 > 0:04:55They rise from the sea floor 15,000 feet to the surface
0:04:55 > 0:04:59and then continue for an almost equal height above it,
0:04:59 > 0:05:03so they can truly be reckoned the highest mountains in the world.
0:05:04 > 0:05:07As we climb up their sides towards the surface,
0:05:07 > 0:05:12we return once more to light and to abundant life.
0:05:18 > 0:05:23Life began in sunlit waters like these some 3,000 million years ago,
0:05:23 > 0:05:27and creatures very similar to those ancient primeval organisms
0:05:27 > 0:05:31still flourish in shallow seas all over the world.
0:05:31 > 0:05:35Feather stars very like these waved their tentacles in the ancient seas
0:05:35 > 0:05:38long before any fish appeared,
0:05:38 > 0:05:41at a time when the land was still bare of life of any kind.
0:05:49 > 0:05:53Horseshoe crabs come from an equally antique stock.
0:05:53 > 0:05:56Fossils of them have been found in rocks 600 million years old.
0:05:56 > 0:05:59Most of their relatives have died out.
0:05:59 > 0:06:02These are the lonely survivors of what was once
0:06:02 > 0:06:04a widespread and successful group.
0:06:23 > 0:06:26Even older, indeed among the first of all living things,
0:06:26 > 0:06:30microscopic plants encased in shells of limestone.
0:06:30 > 0:06:32They use sunshine to build,
0:06:32 > 0:06:35from simple chemicals in the sea water, their own tissue.
0:06:35 > 0:06:39This act of photosynthesis, transforming mineral into vegetable,
0:06:39 > 0:06:42is the basis of all life in the sea.
0:06:47 > 0:06:49A myriad of creatures feed on them.
0:06:49 > 0:06:53Some are tiny animals, that are scarcely bigger than the plants
0:06:53 > 0:06:55that they waft into their mouths.
0:07:01 > 0:07:05This floating community of plants and animals is the plankton.
0:07:05 > 0:07:09Its members move endlessly through the blue seas.
0:07:09 > 0:07:12Many are fragile constructions of jelly that would collapse
0:07:12 > 0:07:14without the support of water.
0:07:24 > 0:07:28Some are colonial, several feet long.
0:07:36 > 0:07:39They call this Venus's girdle.
0:07:39 > 0:07:40It's two feet across.
0:07:40 > 0:07:42Light catches in the beating hairs
0:07:42 > 0:07:44that ripple over its body
0:07:44 > 0:07:46as it moves slowly through the water.
0:07:49 > 0:07:53The animals of the plankton, all those that can't photosynthesise,
0:07:53 > 0:07:57sweep up the tiny plants and other edible particles
0:07:57 > 0:07:59in many different ways.
0:08:01 > 0:08:04This one extends a forest of long tentacles
0:08:04 > 0:08:06in which smaller organisms get entangled.
0:08:09 > 0:08:12This, transparent as glass, trails stinging threads
0:08:12 > 0:08:15and pulls them in whenever they catch something.
0:08:29 > 0:08:32Worms actively pursue their prey.
0:08:40 > 0:08:43Creatures from many families of animals
0:08:43 > 0:08:46have representatives in this community.
0:08:46 > 0:08:49Some are permanent members, some only temporary,
0:08:49 > 0:08:53joining it when they are young larvae and drifting great distances
0:08:53 > 0:08:55before they grow up, change shape
0:08:55 > 0:08:58and settle down to a more static life.
0:08:58 > 0:09:00But all are ultimately dependent
0:09:00 > 0:09:03on the tiny microscopic plants.
0:09:13 > 0:09:16There is another way in which the drifting particles of food
0:09:16 > 0:09:17can be gathered.
0:09:17 > 0:09:20Instead of moving with the current, you can stay fixed to the rocks
0:09:20 > 0:09:23and allow the currents to bring food to you.
0:09:23 > 0:09:27That is the technique used by anemones and many other creatures.
0:09:29 > 0:09:33As the water sweeps by, the particles it carries
0:09:33 > 0:09:35stick to the waving tentacles.
0:09:46 > 0:09:49All kinds of creatures live in this fashion.
0:09:49 > 0:09:51This is a sea cucumber.
0:09:57 > 0:10:00And this, a basket star.
0:10:11 > 0:10:15The water brings not only food, but vital oxygen.
0:10:15 > 0:10:17If it doesn't bring it fast enough,
0:10:17 > 0:10:21it can be speeded by pulsing, as these coral polyps are doing.
0:10:26 > 0:10:28It's not only relatively simple creatures
0:10:28 > 0:10:31like anemones and corals that filter currents.
0:10:31 > 0:10:35Other more complex animals have also taken to doing so.
0:10:35 > 0:10:37This is a remote relative of the shrimps
0:10:37 > 0:10:41that has settled down on its back, grown a protective shell
0:10:41 > 0:10:44and fishes for the passing particles with its feet.
0:10:52 > 0:10:54It's a barnacle.
0:10:58 > 0:11:02Some crabs also rely on the currents to bring them meals,
0:11:02 > 0:11:05and pluck them from the water with tiny pincers.
0:11:10 > 0:11:12But the biggest of all filter-feeders
0:11:12 > 0:11:16propel themselves gently through the surface waters.
0:11:22 > 0:11:26A manta ray, 18 feet across.
0:11:26 > 0:11:28It often feeds at night
0:11:28 > 0:11:31when dense swarms of the plankton move up towards the surface.
0:11:31 > 0:11:34The water is channelled into its mouth
0:11:34 > 0:11:36by the blades on either side of its head,
0:11:36 > 0:11:38and then passes through filters
0:11:38 > 0:11:40in the slits in the sides of its throat.
0:11:46 > 0:11:52The basking shark gathers the same sort of food in a similar way.
0:11:52 > 0:11:54It grows even bigger than the manta -
0:11:54 > 0:11:5740 feet long and four tons in weight.
0:12:00 > 0:12:06Idling through the water, it filters over 1,000 tons of water every hour.
0:12:17 > 0:12:20And even bigger still - in fact, the biggest of all fish -
0:12:20 > 0:12:22the whale shark.
0:12:24 > 0:12:28This mountain of a creature can be up to 50 feet long.
0:12:40 > 0:12:44Other, more normal-sized fish live on and around it.
0:12:44 > 0:12:47Some collect its refuse.
0:12:55 > 0:12:59Others pick off morsels that get stuck in its tiny teeth
0:12:59 > 0:13:02in a mouth six feet wide.
0:13:03 > 0:13:07It's an astonishing proof of how sustaining and how abundant
0:13:07 > 0:13:08the plankton must be.
0:13:19 > 0:13:25But of course, not all sharks live on plankton or are quite so amiable.
0:13:28 > 0:13:32These are grey reef sharks, about six feet long.
0:13:42 > 0:13:46It's some consolation to know that those sharks
0:13:46 > 0:13:48don't normally attack human beings.
0:13:48 > 0:13:54Their prey is usually small fish or predators.
0:13:55 > 0:13:58And indeed, when one looks at them,
0:13:58 > 0:14:03it is not so much their danger that comes into your mind
0:14:03 > 0:14:05as their extraordinary beauty.
0:14:05 > 0:14:08The way in which they are so perfectly streamlined,
0:14:08 > 0:14:11every curve of their body, every curve of their fins
0:14:11 > 0:14:16precisely matching the shape that is needed to glide through the water
0:14:16 > 0:14:19with the least struggle.
0:14:19 > 0:14:21Most beautiful things.
0:14:22 > 0:14:26Sharks belong to a very ancient family that evolved this shape
0:14:26 > 0:14:28some 400 million years ago.
0:14:28 > 0:14:30But soon after they appeared,
0:14:30 > 0:14:33another group of fish established itself.
0:14:34 > 0:14:38These have skeletons of bone, not gristle as the sharks have,
0:14:38 > 0:14:41and they have two swimming aids that the sharks lack -
0:14:41 > 0:14:45swim bladders that give them buoyancy
0:14:45 > 0:14:47and paired fins that can twist in all directions
0:14:47 > 0:14:50and so give them great manoeuvrability in the water.
0:14:50 > 0:14:55These bony fish are the ones which today dominate the seas.
0:15:21 > 0:15:26Among them are the most powerful of all hunters in the sea - the tuna.
0:15:26 > 0:15:30When hunting, they can swim faster than any other fish.
0:15:30 > 0:15:32Some say nearly 70 miles an hour,
0:15:32 > 0:15:35faster even than a cheetah can run on land.
0:15:35 > 0:15:40But the fish's dominance of the sea didn't go unchallenged.
0:15:40 > 0:15:43Some ten million years ago, warm-blooded creatures from the land
0:15:43 > 0:15:48invaded the sea, mammals, and they became equally streamlined.
0:16:17 > 0:16:22Dolphins and killer whales are descended from four-footed,
0:16:22 > 0:16:26land-living, air-breathing mammals that were flesh-eaters.
0:16:26 > 0:16:28In the sea, they lost their limbs
0:16:28 > 0:16:31but not their taste for meat, nor their teeth.
0:16:31 > 0:16:34Indeed, one of the family that lives only in the ice-strewn waters
0:16:34 > 0:16:39of the Arctic has grown one of its teeth to an extraordinary length.
0:16:48 > 0:16:51These are narwhals, and they are all males,
0:16:51 > 0:16:55for only the male produces the great tusk, up to nine feet long.
0:16:59 > 0:17:03These without tusks are females, one with a calf.
0:17:03 > 0:17:05And these are young males.
0:17:11 > 0:17:15No-one knows for certain what purpose the tusk serves,
0:17:15 > 0:17:18but it seems likely that it is used in courtship.
0:17:18 > 0:17:22That is confirmed by the fact that very rarely indeed
0:17:22 > 0:17:26males have been glimpsed, as here, fencing with one another.
0:17:52 > 0:17:56The best view that most of us can get for most of the time
0:17:56 > 0:18:00of most kinds of whales, is a brief glimpse
0:18:00 > 0:18:03as the animal comes to the surface to snatch a breath,
0:18:03 > 0:18:06but that's not the case with the beluga,
0:18:06 > 0:18:08these beautiful white whales.
0:18:08 > 0:18:14Up here in the Canadian Arctic, they come just during those brief weeks
0:18:14 > 0:18:17when the ice goes away from these shores,
0:18:17 > 0:18:21and assemble in vast numbers in this bay.
0:18:21 > 0:18:25There are hundreds, sometimes as many as a thousand.
0:18:32 > 0:18:35We don't really know why they come here, nor what they do
0:18:35 > 0:18:37now that they are here.
0:18:37 > 0:18:40Maybe there is some kind of specially attractive food
0:18:40 > 0:18:42in these shallow waters,
0:18:42 > 0:18:44for sometimes they seem to deliberately to stir up
0:18:44 > 0:18:46the gravelly bottom of the bay.
0:18:46 > 0:18:50Perhaps there is valuable food for youngsters or nursing mothers,
0:18:50 > 0:18:55for many that come are females with babies a few months old,
0:18:55 > 0:18:57swimming skilfully in their mother's slipstream.
0:18:57 > 0:19:00But whatever it is that they do here,
0:19:00 > 0:19:03they seem to be enjoying themselves hugely.
0:19:08 > 0:19:10And they haven't lost their mammalian habit
0:19:10 > 0:19:11of communicating by sound.
0:19:11 > 0:19:16So vocal are they that they are sometimes called sea canaries.
0:19:23 > 0:19:28The most recent family to colonise the sea, also mammals,
0:19:28 > 0:19:30were descended from bear-like creatures.
0:19:30 > 0:19:34The walrus and its cousin the seals are not so fully adapted
0:19:34 > 0:19:36to life in the sea as the whales,
0:19:36 > 0:19:39but then they haven't been there so long.
0:19:45 > 0:19:48They haven't lost their feet as the whales have,
0:19:48 > 0:19:52nor do they spend all their lives in the water.
0:19:55 > 0:19:56They come ashore to give birth
0:19:56 > 0:19:59and they often haul themselves out to rest.
0:19:59 > 0:20:01Nonetheless, they are superb swimmers.
0:20:10 > 0:20:13So, in the 3,000 million years
0:20:13 > 0:20:16since living organisms first appeared in the sea,
0:20:16 > 0:20:19the oceans have acquired a population of immense diversity,
0:20:19 > 0:20:22from simple single-celled microscopic plants
0:20:22 > 0:20:26to advanced and complex highly intelligent mammals.
0:20:26 > 0:20:30Indeed, there are more different groups of animals living in the sea
0:20:30 > 0:20:31than there are on land.
0:20:34 > 0:20:37The oceans were the birthplace and the nursery of life,
0:20:37 > 0:20:40and they are still its main residence.
0:21:34 > 0:21:37But the sea is not uniform.
0:21:37 > 0:21:40Just as the land has different, specialised environments
0:21:40 > 0:21:44inhabited by creatures that occur nowhere else, so does the sea.
0:21:44 > 0:21:48The coral lagoon is a world of its own.
0:21:48 > 0:21:51Corals are very demanding in their requirements.
0:21:51 > 0:21:54They must have good light, clear, unpolluted water, and warmth,
0:21:54 > 0:21:59and they find those conditions in their very best in the tropics,
0:21:59 > 0:22:01particularly around the small islands that are the summits
0:22:01 > 0:22:04of submarine mountains. There, they flourish so well
0:22:04 > 0:22:07that they grow outwards into the clear blue water,
0:22:07 > 0:22:09building on top of their own skeletons
0:22:09 > 0:22:12to form these wide, shallow lagoons.
0:22:16 > 0:22:21The variety of corals is immense. Some are soft and rubbery,
0:22:21 > 0:22:24others are hard and slightly flexible, like a horn.
0:22:24 > 0:22:26But most are stony.
0:22:26 > 0:22:30The organisms that build these structures, ton upon ton,
0:22:30 > 0:22:32occupy only the outer skin.
0:22:32 > 0:22:34The rest is dead.
0:22:34 > 0:22:37As they develop, the little organisms branch,
0:22:37 > 0:22:41and the particular way they do so determines the shape of the colony,
0:22:41 > 0:22:46forming antlers and organ pipes, whips and fans, vases and buttons.
0:23:01 > 0:23:05If the jungle is the place on land
0:23:05 > 0:23:08where there are the greatest number
0:23:08 > 0:23:11and the greatest variety of life,
0:23:11 > 0:23:15then this, the coral reef,
0:23:15 > 0:23:19is surely the jungle of the sea.
0:23:19 > 0:23:21The number, the variety,
0:23:21 > 0:23:25the sheer beauty of all these myriad fish,
0:23:25 > 0:23:27corals and anemones,
0:23:27 > 0:23:29is quite breathtaking.
0:23:31 > 0:23:36Of course, the tiny anemone-like creatures that build these fans
0:23:36 > 0:23:40and fronds of coral are themselves animals.
0:23:40 > 0:23:42But within their tissues,
0:23:42 > 0:23:50there are tiny granules which are algae, plants,
0:23:50 > 0:23:53and it's they that harness the sunshine
0:23:53 > 0:23:58and use it to build living tissue.
0:23:58 > 0:24:01And onto these plates and branches of coral
0:24:01 > 0:24:06come a wide variety of creatures to browse.
0:24:06 > 0:24:10Some, like the parrotfish, bite off chunks.
0:24:10 > 0:24:14Others pick off little organisms and particles with the utmost delicacy.
0:24:32 > 0:24:36The tides, surging in and out of the lagoon,
0:24:36 > 0:24:40bring in regular supplies of fresh oxygenated water and fresh food.
0:24:40 > 0:24:43Angler fish sit in the current waiting patiently,
0:24:43 > 0:24:46like all fishermen, for whatever turns up.
0:24:46 > 0:24:50Even such specialised fish as these exist on the reef
0:24:50 > 0:24:53in several different versions. There's this lemon-yellow one
0:24:53 > 0:24:56that angles with a movable spine on its forehead.
0:25:02 > 0:25:06Little reef fish find it an irresistible bait.
0:25:14 > 0:25:18More prey to be angled for by the decoy fish.
0:25:26 > 0:25:30A dorsal fin patterned with a false eye and mouth
0:25:30 > 0:25:32so that it looks remarkably like a little fish
0:25:32 > 0:25:35and therefore may attract other small fish -
0:25:35 > 0:25:37or possibly predatory ones.
0:25:37 > 0:25:40This one is the wrong way round.
0:25:40 > 0:25:42Its spines would stick in the mouth.
0:25:46 > 0:25:48That's better.
0:25:48 > 0:25:51One of the fastest actions in the animal world.
0:25:54 > 0:25:57And the angler, perhaps to prevent a second fish arriving
0:25:57 > 0:26:00before it has properly digested the first,
0:26:00 > 0:26:03changes colour so that the lure vanishes.
0:26:09 > 0:26:12In the reef, there are many species with many ways of life.
0:26:12 > 0:26:15Just take the crustaceans, for example.
0:26:15 > 0:26:17Hermit crabs live by scavenging.
0:26:17 > 0:26:20Often, they share the shells they have commandeered
0:26:20 > 0:26:22as a home with anemones.
0:26:22 > 0:26:26The anemones benefit by picking up bits of the crab's meal
0:26:26 > 0:26:29and giving the crab in return a certain protection
0:26:29 > 0:26:32with their stinging tentacles.
0:26:32 > 0:26:36This crab actually uses a particular kind of anemone as a weapon,
0:26:36 > 0:26:40wearing one on each claw like boxing gloves.
0:26:41 > 0:26:45This one tries to put on a sponge like an overcoat.
0:26:45 > 0:26:48It seems to be rather overdoing things, for the brown jersey
0:26:48 > 0:26:51it's already wearing is also a sponge, and a well-established one.
0:26:51 > 0:26:54But the arrangement will suit both parties.
0:26:54 > 0:26:57The crab gets the camouflage, and the sponge may benefit
0:26:57 > 0:26:58from the crab's crumbs.
0:27:04 > 0:27:07Crabs and their relations, the lobsters and shrimps,
0:27:07 > 0:27:10are found from top to bottom of the reef.
0:27:10 > 0:27:14Big ones like this lobster prowl openly through the coral branches.
0:27:19 > 0:27:23Little ones like the mantis shrimp are rather more cautious
0:27:23 > 0:27:25and build themselves tunnels.
0:27:34 > 0:27:37If the coral reef is the equivalent of the jungle,
0:27:37 > 0:27:40than maybe these waving beds of kelp
0:27:40 > 0:27:43in the cold Atlantic waters off the coast of Norway
0:27:43 > 0:27:46are like the dark evergreen forests of the north -
0:27:46 > 0:27:52bitterly cold, dense and uniform, and swept by raging gales.
0:28:12 > 0:28:16Bleak though the kelp forest may seem, there are riches here,
0:28:16 > 0:28:18and eider duck know it.
0:28:30 > 0:28:33The eiders settle in flocks on the surface of the water
0:28:33 > 0:28:35above the kelp forest,
0:28:35 > 0:28:37and they are almost as adept in flying through the water
0:28:37 > 0:28:39as they are through the air.
0:28:56 > 0:29:00This is what they seek - mussels.
0:29:09 > 0:29:11Eiders are true creatures of the sea,
0:29:11 > 0:29:14seldom, if ever, visiting fresh water.
0:29:14 > 0:29:19They prefer to fish for mussels on an ebb tide when the water is low,
0:29:19 > 0:29:22but they are such good swimmers that they can stay below water
0:29:22 > 0:29:25for a minute or more, and dive down to 50 feet below the surface.
0:29:35 > 0:29:39The streaming current causes great problems
0:29:39 > 0:29:40to the fish of the kelp forest.
0:29:40 > 0:29:43Simply maintaining a position there is a struggle.
0:29:43 > 0:29:47The lumpsucker does it with modified fins on its underside,
0:29:47 > 0:29:51and gets such a firm grip that it is extremely difficult
0:29:51 > 0:29:53to pull it off, even by hand.
0:29:53 > 0:29:56Its young develop suckers at a very early age
0:29:56 > 0:29:58and sometimes fix themselves to their father,
0:29:58 > 0:30:00who ferries them off to deeper waters.
0:30:03 > 0:30:07Kelp grows in coastal waters all round the world,
0:30:07 > 0:30:10and in the seaweed forests of southern Australia
0:30:10 > 0:30:13lives one of the most extravagantly camouflaged of all fish.
0:30:23 > 0:30:26Other fish appear to be completely deceived.
0:30:26 > 0:30:28This small one, itself with a false eye
0:30:28 > 0:30:31so that it is difficult to tell whether it is coming or going,
0:30:31 > 0:30:36lives in these green leafy tatters as though they were real plants -
0:30:36 > 0:30:37but they're not.
0:30:37 > 0:30:42They're all part of the elaborate costume of the leafy seadragon.
0:31:12 > 0:31:16The dragon is really a kind of seahorse,
0:31:16 > 0:31:19as you can recognise if you can disentangle its main body
0:31:19 > 0:31:21from all its extraordinary outgrowths.
0:31:21 > 0:31:22And like its relatives,
0:31:22 > 0:31:26it has a tiny mouth with which it picks up small floating shrimps
0:31:26 > 0:31:31that ill-advisedly take shelter in what appears to be floating weed.
0:32:04 > 0:32:09As well as its forests, the sea has its deserts.
0:32:09 > 0:32:11Over vast areas of the ocean floor,
0:32:11 > 0:32:15there is nothing but shifting wastes of sand.
0:32:16 > 0:32:20It seems as lifeless as a desert on land in the heat of the day.
0:32:24 > 0:32:29An occasional fish wanders over the rippled surface as though lost.
0:32:31 > 0:32:34Here and there, a sea urchin levers itself along,
0:32:34 > 0:32:37extracting what nutriment it can find
0:32:37 > 0:32:38from particles within the sand.
0:32:43 > 0:32:46The goatfish looks for the same sort of thing,
0:32:46 > 0:32:49using sensitive barbels on its chin.
0:32:56 > 0:33:00To build a home or a shelter in sand demands special techniques.
0:33:00 > 0:33:05Garden eels cement the grains together with mucus to form a tube
0:33:05 > 0:33:06in which they cling with their tails
0:33:06 > 0:33:09while collecting plankton with their mouths.
0:33:11 > 0:33:15Bulldozer shrimps and a goby cooperate to build a shared tunnel,
0:33:15 > 0:33:17using coral rubble to prop up the roof.
0:33:37 > 0:33:41The bladefish can improvise a shelter on the spur of the moment.
0:33:50 > 0:33:53There are two very different reasons for hiding.
0:33:53 > 0:33:57The bladefish does it to get out of trouble.
0:33:59 > 0:34:01This little cuttlefish does it...
0:34:04 > 0:34:06..in order to cause trouble.
0:34:20 > 0:34:23The prey is a shrimp.
0:34:49 > 0:34:53And the cuttlefish has the shrimp firmly in its tentacles.
0:35:07 > 0:35:09The floating pastures of plankton
0:35:09 > 0:35:12on which so many ocean-going fish depend
0:35:12 > 0:35:15must live in the surface waters within the reach of sunshine.
0:35:15 > 0:35:18The coral lagoon and the kelp forests
0:35:18 > 0:35:21only flourish where good light reaches the bottom.
0:35:21 > 0:35:25But light can't penetrate much beyond 350 feet,
0:35:25 > 0:35:29and most of the ocean floor lies far deeper that that.
0:35:37 > 0:35:39Even quite near the surface
0:35:39 > 0:35:42you often have to take your own light with you.
0:35:52 > 0:35:54Fish, too, carry lights.
0:35:59 > 0:36:03The flashlight fish use theirs to find their food
0:36:03 > 0:36:06and to maintain contact with one another
0:36:06 > 0:36:08like other species in deeper water.
0:36:10 > 0:36:13Their batteries are little colonies of bacteria living in a pouch
0:36:13 > 0:36:15beneath the fish's eye
0:36:15 > 0:36:18that give off light as a by-product of their chemistry,
0:36:18 > 0:36:21and the fish turns its lights off and on
0:36:21 > 0:36:23by raising and lowering a flap of skin.
0:36:28 > 0:36:31At greater depths, giant amphipods, primitive relatives
0:36:31 > 0:36:35of the horseshoe crabs, plod along the bottom.
0:36:35 > 0:36:39Very little is known about these strange creatures.
0:37:01 > 0:37:05Even at 3,000 feet down, there is life.
0:37:05 > 0:37:09Almost all the creatures here feed on dead bodies that fall from above.
0:37:09 > 0:37:12The eel-like hagfish, which have no jaws,
0:37:12 > 0:37:15knot themselves against the carcass to get a better hold.
0:37:29 > 0:37:32Bigger fish grip with their teeth and spin,
0:37:32 > 0:37:34tearing off strips of the flesh.
0:37:36 > 0:37:40The smaller particles drifting down from the surface
0:37:40 > 0:37:43are collected by deep-sea stars and smaller fish.
0:37:43 > 0:37:46It is here that all the nutrients produced by decay
0:37:46 > 0:37:48finally collect as ooze.
0:37:48 > 0:37:52The very deepest parts of the ocean lie below the paths of currents,
0:37:52 > 0:37:56so the water is not only black and cold, but almost still.
0:37:58 > 0:38:03The weird tripod fish perches on its extended fins and its tail.
0:38:09 > 0:38:12Even in the deepest place of all, the Mariana trench,
0:38:12 > 0:38:15seven miles down, there is life.
0:38:15 > 0:38:18Shrimps are slowly picking clean the skeleton of a fish
0:38:18 > 0:38:22that may have taken months to drift down to these still depths.
0:38:29 > 0:38:33But at the surface of the sea, the water is never still.
0:38:45 > 0:38:48Storms whip it up into great waves
0:38:48 > 0:38:50which may travel for hundreds of miles
0:38:50 > 0:38:54before, eventually, they crash into the coasts.
0:39:04 > 0:39:06The water in these waves doesn't travel far,
0:39:06 > 0:39:09but circulates more or less in the same place
0:39:09 > 0:39:12while the wave itself moves on.
0:39:12 > 0:39:14But that circulation
0:39:14 > 0:39:16is of crucial importance to the creatures of the sea,
0:39:16 > 0:39:19for it is this that allows the waters of the sea
0:39:19 > 0:39:23to absorb the vital oxygen from the air above.
0:40:02 > 0:40:05But deep currents do move through the oceans.
0:40:05 > 0:40:08They are created by the spin of the earth
0:40:08 > 0:40:11which gives the waters at the equator a westward drift,
0:40:11 > 0:40:14and by the sun which warms these equatorial waters
0:40:14 > 0:40:17and sends them away to the poles.
0:40:17 > 0:40:21This produces vast ocean-wide eddies that replicate the whirlpools
0:40:21 > 0:40:27of tidal races, but do so on a scale that is thousands of miles across.
0:40:32 > 0:40:35In the Pacific, the equatorial current divides,
0:40:35 > 0:40:38and in the south it flows down as far as New Zealand.
0:40:41 > 0:40:45In the Indian Ocean, the southern system is almost circular.
0:40:45 > 0:40:48The northern has to swirl around the great triangle of India.
0:40:50 > 0:40:55In the Atlantic, the north-flowing current is called the Gulf Stream,
0:40:55 > 0:40:58and it encloses, in the centre of the ocean,
0:40:58 > 0:41:00as all these great whirlpools do,
0:41:00 > 0:41:02an area where the waters are almost still.
0:41:04 > 0:41:08On their surface float rafts of weed.
0:41:08 > 0:41:09It never roots but floats for ever,
0:41:09 > 0:41:13rocked sufficiently by the swell to prevent its topmost fronds
0:41:13 > 0:41:15from drying out in the sun.
0:41:22 > 0:41:25The Portuguese sailors, looking at the little bladders
0:41:25 > 0:41:29that keep it afloat, called them sargasso - grapes.
0:41:29 > 0:41:31This is the Sargasso Sea.
0:41:31 > 0:41:33Like every other region within the oceans,
0:41:33 > 0:41:36it has its own specialised inhabitants.
0:41:38 > 0:41:43Small fish shelter in its fronds and are closely disguised to match them,
0:41:43 > 0:41:48and swimming crabs clamber up and rest on top of the floating mats.
0:41:48 > 0:41:52But the Sargasso is one of the least fertile stretches of water
0:41:52 > 0:41:54in all the oceans.
0:41:54 > 0:41:57Since no currents feed into it, it receives no nutrients
0:41:57 > 0:42:01and its clear waters are largely barren.
0:42:06 > 0:42:08But patches of it occasionally break away.
0:42:11 > 0:42:14Between the Gulf Stream and the North American coast,
0:42:14 > 0:42:17there are cores of cold Sargasso water
0:42:17 > 0:42:19surrounded by warm circulating currents
0:42:19 > 0:42:22formed when the Gulf Stream begins to meander
0:42:22 > 0:42:24and nips off a segment of the Sargasso,
0:42:24 > 0:42:27complete with its weed and populations of animals.
0:42:27 > 0:42:30These warm core-rings, a hundred or so miles across,
0:42:30 > 0:42:32drift slowly down the coast
0:42:32 > 0:42:35until they lose their momentum and their warmth,
0:42:35 > 0:42:38break up and are swept away again by the Gulf Stream.
0:42:39 > 0:42:44The Gulf Stream continues northwards along the coast to Newfoundland.
0:42:46 > 0:42:49Here, off these bleak fogbound beaches,
0:42:49 > 0:42:52it creates an area of seas that might be reckoned to be
0:42:52 > 0:42:55one of the most fertile and productive places
0:42:55 > 0:42:56on the entire globe, a place
0:42:56 > 0:42:59where the full potential richness of the ocean is realised,
0:42:59 > 0:43:03and where animals of all kinds above and below the water
0:43:03 > 0:43:05come to harvest it.
0:43:08 > 0:43:14The warm water of the Gulf Stream is accompanied by steady warm breezes.
0:43:14 > 0:43:20And just about here, it meets a cold current coming down from the Arctic,
0:43:20 > 0:43:25and where the warm breezes meet the icy breath of the Arctic,
0:43:25 > 0:43:29they shed their moisture and form these fogs.
0:43:29 > 0:43:34And where the two currents meet, the waters churn and swirl,
0:43:34 > 0:43:38and bring up rich nutrients from the bottom of the sea.
0:43:38 > 0:43:42Now, it so happens that just off this coast
0:43:42 > 0:43:45there is an underwater plateau where the water is so shallow
0:43:45 > 0:43:50that the sun or the light can get almost always to the bottom,
0:43:50 > 0:43:53and so the floating plants of the sea
0:43:53 > 0:43:55are always within the range of light,
0:43:55 > 0:43:59and they're fed eternally by these swirling currents
0:43:59 > 0:44:01bringing up nutrients.
0:44:01 > 0:44:06So the plants flourish, and on them come great shoals of fish
0:44:06 > 0:44:09which breed and spawn in such numbers
0:44:09 > 0:44:13that at times the waters seem almost to boil with them.
0:44:13 > 0:44:18These are capelin, a small fish related to the European smelt.
0:44:18 > 0:44:21They feed on the plankton in the surface waters,
0:44:21 > 0:44:25and in May they gather in vast shoals to spawn.
0:44:25 > 0:44:27Some will do so offshore,
0:44:27 > 0:44:31but some go to extraordinary trouble to lay their eggs out of water
0:44:31 > 0:44:34where they will be safe from other hungry fish.
0:44:36 > 0:44:40The shoals come closer and closer inshore.
0:44:48 > 0:44:52Each female capelin can produce 10,000 eggs.
0:44:52 > 0:44:56Each wave brings in tens of thousands of fish,
0:44:56 > 0:44:57again and again.
0:44:57 > 0:45:00The number of eggs defies any computation.
0:45:00 > 0:45:04They pile up in banks, as solid as sand along the high-water mark.
0:45:06 > 0:45:11Having spawned, all the males and most of the females die.
0:45:25 > 0:45:28The richness that the capelin gathered from the plankton
0:45:28 > 0:45:32and converted into their own flesh is now gathered by birds.
0:45:33 > 0:45:37Shearwaters gorge themselves on the dying and the dead.
0:45:49 > 0:45:53Gannets dive between the scavengers, taking the live fish.
0:45:58 > 0:46:01And still the capelin come in.
0:46:01 > 0:46:05Even before they get to the shallows, they are hunted.
0:46:07 > 0:46:11Herds of seals come up to the Grand Banks specially at this time
0:46:11 > 0:46:13to share in the bonanza.
0:46:59 > 0:47:02And here, too, come the biggest hunters of all.
0:47:08 > 0:47:10Humpbacked whales.
0:47:20 > 0:47:24With each upward lunge, the whale takes in tons of water
0:47:24 > 0:47:26and thousands of capelin.
0:47:33 > 0:47:37With a mouthful in its jaws, it brings forward its tongue,
0:47:37 > 0:47:40squirts out the surplus water through the filter plates
0:47:40 > 0:47:43that hang from its upper jaw and swallows the tiny fish.
0:48:06 > 0:48:10The whales have developed a way of concentrating the capelin shoals
0:48:10 > 0:48:14so that they will get the greatest number of fish in a single mouthful.
0:48:14 > 0:48:17It's called bubble-netting.
0:48:17 > 0:48:21Those white areas are huge masses of bubbles.
0:48:21 > 0:48:24The whales dive deep below the swarming capelin
0:48:24 > 0:48:27and start a slow, spiralling swim upwards,
0:48:27 > 0:48:30blowing gusts of bubbles as they rise.
0:48:30 > 0:48:33The capelin, frightened by the circular curtain of bubbles,
0:48:33 > 0:48:36rush inwards and form a dense, confused shoal.
0:48:36 > 0:48:39Than the whale rises up in the middle, jaws agape,
0:48:39 > 0:48:41and engulfs the lot.
0:48:52 > 0:48:53After a few short weeks,
0:48:53 > 0:48:56the spawning orgy of the capelin is over.
0:48:56 > 0:49:00Their bodies lie in vast drifts awaiting the processes of decay
0:49:00 > 0:49:02which will return their nutrients to the waters,
0:49:02 > 0:49:06but even before they disperse, other bodies appear.
0:49:06 > 0:49:07Dead squid.
0:49:09 > 0:49:11Nobody knows where they have come from,
0:49:11 > 0:49:13or why they have died in such numbers,
0:49:13 > 0:49:16but these blizzards of bodies appear most years in July,
0:49:16 > 0:49:19and are a sign that shoals of the living animals are about to arrive.
0:49:30 > 0:49:33They will bite any small, moving thing.
0:49:33 > 0:49:36To catch them, you don't even need bait.
0:49:36 > 0:49:39They simply impale themselves on a naked hook,
0:49:39 > 0:49:43so that most summers, fishing villages on the Newfoundland coast
0:49:43 > 0:49:47go jigging for squid, hauling them out by the thousands.
0:50:01 > 0:50:05As they're hooked, they puff out clouds of squid ink.
0:50:13 > 0:50:17Hundreds of tons of them are despatched every year to Japan,
0:50:17 > 0:50:20where they are a much-prized food.
0:50:25 > 0:50:29Mackerel also come to the Grand Banks by the millions
0:50:29 > 0:50:32to feed on small plankton-feeding fish.
0:50:33 > 0:50:38They're netted by the ton by fleets of factory ships,
0:50:38 > 0:50:40and their rich flesh is valued all over the world.
0:50:42 > 0:50:45But even the Grand Banks are not inexhaustible.
0:50:47 > 0:50:49During this century, man has fished
0:50:49 > 0:50:52so skilfully, so intensively, so unrelentingly,
0:50:52 > 0:50:56that he has begun to change the pattern of life in the sea.
0:50:56 > 0:51:00Some kinds of fish have been forced to change their habits,
0:51:00 > 0:51:03others have been driven close to the edge of extinction.
0:51:03 > 0:51:05And this little port in Newfoundland,
0:51:05 > 0:51:09close to what was once the richest of all seas,
0:51:09 > 0:51:12is now bringing in fewer and fewer catches,
0:51:12 > 0:51:15and modern fish-processing plants like that one
0:51:15 > 0:51:17are standing for much of the time, idle.
0:51:17 > 0:51:20So man has changed the sea,
0:51:20 > 0:51:23just as he's changed almost every other environment in the world.
0:51:23 > 0:51:25But he's done something else, too.
0:51:25 > 0:51:27He's created new environments,
0:51:27 > 0:51:31environments of brick and concrete, and chromium and plastic.
0:51:31 > 0:51:35And it's those, the latest of the world's environments,
0:51:35 > 0:51:37and the ways in which plants and animals
0:51:37 > 0:51:39have adapted to live in them,
0:51:39 > 0:51:42that we're going to look at in the last of these programmes.
0:52:23 > 0:52:26Subtitles by Red Bee Media Ltd