A storm approaches at Rum Point, Grand Cayman, one of the best places to witness a bioluminescence display

It is a moonless Caribbean night and, apart from a few twinkling stars, the only light comes from the sea immediately around our four kayaks. The boats have a halo of pale gold and leave shimmering trails in their wake. Every time our paddles lift out of the water they drip molten gold as if they’d been touched by a watery Midas.

Old men who once fished for silversides and sprats here, or dried sharkskins along the shore to make sandpaper, know all about this magical, monthly light show. But visitors to the Cayman Islands rarely get to hear about it, let alone experience it.

Bioluminescence, or light created by plants and creatures, occurs all over the world but rarely in such spectacular concentration. We plunge our hands and feet into the sea and watch tiny spangles of light illuminate our skin. Silence has fallen on our chattering group of eight, awestruck by the underwater fireworks.

A splash shatters the peace. Tom Watling, our young Cayman guide on this night-time adventure, has dived into the sea. He is shining like a Renaissance angel in flight, somersaulting downwards until we can no longer see him.

Suddenly he reappears in a burst of light on the far side of our kayaks. Shaking spangles of water out of his hair, he tells us about the alien world below, where dinoflagellates – tiny plants that obtain energy from sunlight and then, in darkness, emit light in response to movement in the water, thus creating bioluminescence – bounced explosions of light against his eyeballs.

“I once scuba-dived here with a friend,” says 24-year-old Watling, who set up Cayman Kayaks in 2005. “We took off our masks and sat quietly on the sea floor. Every time we blinked we could see sparkles coming off each other’s eyelashes.”

He first came across bioluminescence aged 14. “I threw a coconut in the water,” he recalls. “It splashed glowing water up into the air and back down again, making ripples of sparkles. Fish shot about under the water like shooting stars.”

The Cayman Islands – made up of Grand Cayman, Cayman Brac and Little Cayman – boast some of the best diving in the world, and wildlife riches ranging from rare blue iguanas and ghost orchids to bioluminescence. Yet few people seek out these treasures. Most visitors stay at Seven Mile Beach, where white sands and dazzling blue sea meet American-style hotels, cocktail bars and nightclubs.

Journey beyond those worldly pleasures and the islands offer another kind of wildlife. I had already discovered the subtle pleasures of mangrove snorkelling in the waters around Grand Cayman, where sea horses drift in a lush forest of underwater greenery. But it wasn’t until last November that I heard about bioluminescence. I flew into Grand Cayman from neighbouring Cuba and drove straight from the airport to meet Watling.

No one is certain why bioluminescence is so bright in a few pockets of sea such as this one but factors include proximity to red mangroves, high light levels and low water movement. The chemical process behind bioluminescence is similar throughout the natural world, from fireflies to glowing mushrooms. That much is understood but less is known about the reasons for marine bioluminescence. The most popular theory is that the light attracts large fish in order to prey on the smaller fish that are feeding on the dinoflagellates.

Either way, bioluminescence makes such a breathtaking display that I join a trip for a second night running. The moon has grown to a slim crescent, making it more difficult to see the light – in theory, at least – which is why these tours happen just once or twice a month. In practice, however, I find that the show is brighter second time round. The colours are still gold and yellow – not the blue that many people describe. Sightings of green and red are also quite common.

Shoals of fish zip through the water, creating sparkling underwater streaks. Below them I can see a large, glowing rectangular shape circling slowly around the sea bed. A ray, probably.

The quality of the luminescence varies. Sometimes it scatters stars along our hands, feet and paddles. Sometimes it creates clouds of light that leave trails across the bay for a minute or so before vanishing back into darkness. I would like to dive into this cooling fire but Watling asks us not to. Too many bodies in the water – with all their attendant bug spray and body lotions – could upset the dinoflagellates.

A couple of miles away, a massive conventional firework display lights up the sky. It’s a local festival, a Caribbean fête with bands, food and partying through the night. But our marine fireworks win the day and we return to sea-gazing. As we peer down into the water a glittering lobster makes his way across the ocean floor. Watling looks at the creature and says he can no longer eat lobster. I see what he means. Bioluminescence puts everything in a new light.

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On the water front

The frequency of bioluminescence tours depend on weather and moon cycles. No previous kayaking experience is needed but participants have to be over the age of 14. Tours last for about one and a half hours and cost from US$59 per person at Cayman Kayaks (tom@caymankayaks.com tel: +345 926 4467; www.caymankayaks.com).

For further information about bioluminescence, the Scripps Institution of Oceanography has an interesting, accessible website (http://siobiolum.ucsd.edu/publications.html).

Sea Elements (www.caymanseaelements.com) offers outstanding mangrove snorkel and boat trips from $40 per person. They are guided by Marnie Laing, who runs the island’s marine environment education programme.

Little Cayman, a short plane ride from Grand Cayman, is ideal for diving.

More information about all three islands can be found at caymanislands.co.uk

I stayed at the Westin Casuarina Resort and Spa (http://westincasuarina.com) on Seven Mile Beach, Grand Cayman, where rooms start at $450 a night.

British Airways flies from London Heathrow to Grand Cayman (via Nassau) from £583.70 return including taxes (www.ba.com).