“As it gets dark, the reef begins to change,” explains naturalist Ryan DeNoyer. “Just like any other city, when the sun goes down, the normal people go to sleep and the weirdos come out.”

As the first stars appear above Seven Mile Beach, flippers and flashlights are handed out to our group, and wetsuits zipped up. I’ve snorkeled off this shore dozens of times before, but never after dark. Joining a nocturnal snorkeling excursion with Jean-Michel Cousteau’s Ambassadors of the Environment – a program of eco-tours and education run in partnership with The Ritz-Carlton – promises a completely different perspective of Cayman’s teeming underwater metropolises.

“One of the things that changes most is the corals themselves,” DeNoyer says. “During the daytime, coral is feeding primarily by photosynthesis. They’re animals, but they have tiny microscopic algae in their tissues, so they’re collecting as much sunlight as they can. But at night, they fire out their stinging tentacles (they’re related to jellyfish) to collect plankton and any other little bits of organic matter that drift by. So, when you go up to them, they actually look fuzzy.”

Like us, many fish put on their pajamas for bedtime, changing color thanks to cells called melanophores in their scales. Blue Tangs fade from a deep indigo to a pale grey-blue, while creamy-colored goat fish take on a red hue. Since red is the first color the eye loses underwater, this makes them almost invisible to predators.

The underwater city analogy is a fitting one, DeNoyer adds, since every organism out there has a job or function. “The coral are the architects or the buildings, providing the structure. The sharks and barracuda are the managers keeping all the lower level employees in check. The landscaping crew is our herbivores, like the urchins and parrotfish.”

So, who are these nocturnal “weirdos” we could run into on the reef? Apparently, it’s a favorite time for the reef’s top predators to come out to hunt, including eels, nurse sharks, stingrays, squid and octopus. Many of the herbivores, therefore, take shelter or adopt adaptations; for example, parrotfish are known to create a protective “sleeping bag” out of mucus.

I’ve learned a lot before even climbing into the water, thanks to the briefing and introductory video at the Ambassadors’ headquarters, a colonial-style pink building within The Ritz-Carlton’s grounds. DeNoyer and fellow guide Andrew McGovern inform us that all the Ambassadors staff members have academic backgrounds in marine biology, environmental science or related disciplines, and aside from these bi-weekly night snorkels, they also lead excursions such as mangrove kayaking and underwater photography. The idea is to introduce people, both hotel guests and Cayman residents, to the island’s natural wonders.

Get a different view of Cayman’s reefs at night-time.

Out on the beach, we walk only a couple of minutes south of the hotel before heading into the sea. I’m surprised: surely, we need to venture much further from civilization to find all the promised wildlife? I can still see the cabanas and hear the music from The Ritz-Carlton’s beachfront barbecue; this is like going on safari in the suburbs of Cape Town.

The beams of our torches pierce the inky water, their narrow rays of light exposing the sandy seabed. Within a few yards, we encounter (or rather, disturb) our first resident: a slumbering Hawksbill turtle. Turtles work on the principle that if they can’t see you, then you can’t see them. After taking a big breath of air, they swim down to a ledge or rock and wedge their head underneath, leaving only their shells exposed. Larger adults can sleep for six hours before they have to come up for air.

Our next spot is a scorpionfish, camouflaged well on the sandy sea floor. No one gets too close to this specimen, and not only because of its gnarled appearance: its fin spines contain a poisonous venom.

As we swim onto Lover’s Reef, the marine life continues to come thick and fast. There are longspine squirrel fish, with silvery-red scales and huge eyes that take up almost the whole side of their head; Rock Beauty angelfish, bright yellow with a distinctive black spot on their sides; a spiny lobster; trunkfish, with their distinctive pointed snouts and pouting lips; a lobster sticking his claws out of his underwater cave, and some bulbous grey pufferfish. Dozens of parrotfish doze on the coral, lying on their sides with their lidless eyes open, as if playing dead.

Down on the seabed are clusters of long-spined black urchins, while a flurry of tiny fish and shrimp fill the water all around us like confetti, feasting on the plankton attracted to our lights. I can feel them colliding with my mask as I swim, a faint but constant pattering like rain.

A spotted eel pokes his head out of a crevice in the coral. DeNoyer says they’re often seen at night looking into every nook they can find in the search for prey. “Occasionally you’ll see a quick jerking movement and then a big bulge moving down when they’ve got something.”

He adds, “The cool thing about these eels is that they’ve actually got a second set of jaws in their throat – kind of like the movie ‘Alien’ – called the Pharyngeal jaws, which pulls the prey down their throat.” Thankfully, the one we encounter is only a juvenile, but the species can grow to more than 13 feet long.

One advantage that night snorkeling offers over scuba diving, I soon realize, is that we get a regular in-water commentary from our guides and can ask questions the moment they pop into our heads. It’s also an accessible option for those who don’t like the idea of being deep underwater or can’t dive due to medical complications (one of our group had an inner ear problem, for example). Of course, you don’t get such extended up-close views of the reef as scuba offers, though the guides dive down to bring up some creatures for us to hold and study, such as a wispy, seven-armed sea star and a queen conch.

After hitting our furthest point out on the reef – about 200 yards from shore – it’s time to switch off our flashlights for a different kind of spectacle. It’s a perfectly clear spring night, and the constellations are so bright and sharp they almost seem close enough to touch. But the stars are competing for attention with the bioluminescence, microscopic organisms that appear as glowing blue specks, shimmering over my arms and legs as I circle them in the water. Sea and sky form a mesmerizing, ethereal mirror-image, both aglow with their own mysterious forces, while we bob there in-between, eight people treading water, feeling small and peaceful.

A Bob Marley tune drifts over from the hotel’s dinner-time entertainment, but we are in another world out here; one that, with its variously spiked, slithering, luminous creatures, shows that Mother Nature can rival the imaginations of the most far-fetched sci-fi writers.