Trevor Norton, marine ecologist, kicks off a series on academics' pastimes and how they feed into their research

At school my speciality was failing exams, but television changed my life forever when marine biologist Hans Hass went Diving to Adventure . Each week he and his luscious wife, Lotte, swam with giant sharks and moray eels for whom every smile was a practice bite. In the spring of 1955, as soon as the sea warmed to merely frigid, I ventured beneath the waves. Begoggled, amphibian-footed and carrying a toasting fork fixed to a bamboo pole, I slid into the cold and cloudy North Sea.

Suddenly, while I was below, something stabbed the water in front of me, a dark javelin in a cone of bubbles. It transformed into a cormorant, making an unsuccessful attempt to capture a sand eel and then escaping back to the sky.

It was the most wonderful thing I had ever seen. I surfaced breathless, more from excitement than lack of air. This, I decided, was the real world. The air-bound attic up there beyond the surface was no place to live. Underwater, weightless and often powerless in the current, I became one with the flow. Wild animals went about their business; a fluttering shoal of pollack parted to let me pass. It was as if the sea had been expecting me. And not a single organism resembled anything on dry land. I had changed planets. Everyone was shocked. It was completely unexpected. I began to pass exams. My A-level project was to strip off all the animals and plants from discrete areas of the shore and follow the patterns of colonisation. In its modest way, the experiment showed me that communities were not static and immutable; they could be changed, at least transiently, by a single disturbance. I had also learnt that scientists find out by doing, not by reading or being told. On this unremarkable shore I began a quest that would last a lifetime.

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The development of diving meant that biologists could at last examine marine communities on the sea floor. Only 60 years ago they were still groping in the dark. Restricted to the surface, they dangled dredges and grabs into the ocean. It was a lucky dip: a little like drifting in a balloon over a fogbound city and dragging up odds and ends from the unseen streets below, and using that as the basis to understand the distribution and behaviour of Liverpudlians.

My own love affair with the sea led me to work on empty shores before the tourists invaded. Immediately after graduating I joined an expedition to Lanzarote. Diving there was like being a Victorian plant hunter venturing into unexplored territory and seeing for the first time species that were known only from decaying scraps washed up by the waves, if they were known at all.

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As a young and green research student, I loved the idea of being a marine ecologist, but didn't know quite what they did. So I played a lot of football. My supervisor worried I might not be fitting in any research and dispatched me to work with Jack Kitching. In 1932, when diving equipment was just a more complicated way to drown, Kitching bought a milk churn, fitted a window, attached a garden hose and put the can on his head as a diving helmet. Armed only with hedging shears to cut through the kelp forest, he trudged below the waves like a ghostly gardener. Although he later became the world authority on the physiology of protozoa, his hobby remained marine biology, so he spent his summers in Ireland where he transformed marine ecological research - and me.

Lough Ine in West Cork proved to be the ideal living laboratory. Kitching showed that, for ecologists, experimentation in the sea was both possible and desirable, as field experiments prevented researchers from embracing seductive explanations that didn't operate in nature. He developed methods to manipulate living systems and goad them into revealing how they functioned. Ecologists in the US followed where he led and the shore and shallow sea became the test-bed for ecological theories. I was privileged to spend 14 wonderful summers with Kitching learning to be a marine ecologist. Almost all my early research on the ecology of kelps was carried out beneath the surface, measuring their productivity and determining the effects of competitors and predators by means of in situ experiments. None of this could have been done without diving, although from the outset fieldwork was augmented with laboratory studies of the stress tolerances of the plants.

Diving is rarely dangerous for the cautious, but being "buzzed" by dozens of rutting bull sea lions in the darkness of a cave was unnerving, and wading in opaque muddy shallows infested with deadly sea snakes was not my favourite pastime. It did carry rather more unsuspected risks as well, such as being shot at by fishermen who thought I was stealing their lobsters or, when I emerged from beneath a pier, being detained on suspicion of trying to blow up the Queen Mother.

When I first went diving 50 years ago, I was reasonably sure that almost everywhere I submerged I was probably the first to see that underwater landscape. Now there are 70,000 sport divers in Britain alone, making 1.5 million dives a year into our coastal waters. There is nowhere in the world so remote that a dive boat doesn't take tourists out to the local reefs and wrecks. The first underwater reserve in the US was established in 1962, but was desecrated by overuse and pollution within 30 years. Precious places can be ruined by overadmiration. I have seen hauntingly beautiful reefs in the Philippines entirely destroyed by dynamite fishing. Nature thrives best on neglect.

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As a teacher and as a researcher communication has always been important to me. When I ceased to descend into the sea, I began to write more about my experiences. Writing comes easily to most scientists, but writing well does not. The editors of scientific journals don't foster style or a sense of humour, although one of my recent articles about plants that had their reproduction regularly curtailed by typhoons was accepted for publication under the title "No whirlwind romance".

Scientists don't have a good public image. Football chief Jose Mourinho, when trying to explain that Chelsea's pitch was better than it looked, strayed into metaphor: "Some people are intelligent but ugly, like scientists." When children were asked to draw a scientist, 90 per cent drew the stereotypically "mad" version. Sharing the excitement of discovery should not be a chore but a pleasure. I unashamedly seek to entertain readers, but without compromising the information. My hope is to interest people who would never dream of going to the Popular Science shelf. When my son was very small, I explained that the Statue of Liberty was a gift from the people of France. His eyes widened and he said: "They must have got a surprise when they opened the parcel."

I would like my readers to get just such a surprise when they open my parcels. Lest anyone should think that I am permanently wrinkled from over-immersion, they should be reassured that increasingly over the years I have worked on the shore. The sea is a place for obsessives. Once you have a taste for the ocean, the intoxication lasts a lifetime. It's not surprising, after all, the world is mostly salty water and so am I. The ocean is truly in my veins and, briefly, when still in the womb, I even had gill slits.

Trevor Norton is emeritus professor at the School of Biological Sciences, Liverpool University. His latest book, Under Water to Get Out of the Rain , a mixture of memoir, history, biography and marine biology, is published by Arrow, ?7.99.

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