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