'The deep sea will come to me': The blackwater diver who photographs the creatures of the deep

When photographer Jialing Cai plunged into the ocean in the dead of night, she found creatures of the deep had risen up to meet her.

In blackwater diving, the ocean floor is invisible, says Jailing Cai. You float in an endless black void.

"There is no reference for you to know your location in this three-dimensional space," says the specialist underwater photographer. "If you're not aware of your depth, you could start sinking down deeper and deeper." 

During her first nighttime dive, however, "the excitement overwhelmed my fear". Cai soon found that this black "empty space" was, in fact, teeming with life – from baby octopuses, jellyfish and crabs, to juvenile fish and all manner of copepods, or "insects of the sea".

Cai, from Chongqing, China, is an award-winning blackwater photographer. In 2023, she was named Oceanographic magazine's Ocean Photographer of the Year for her image of a paper nautilus, a rarely-encountered octopus with a paper-thin shell-like egg case. Then, in 2025, Cai won the Oceanographic Female Fifty Fathoms Award for her collection of photographs that captured some of the ocean's most charismatic visitors from the deep.

Cai doesn't need to dive deep, though, to capture these deep ocean creatures. She simply waits for them to emerge from the depths at night as they come to surface to feed – in what is the biggest mass migration of animals on Earth.

Little is understood about the true nature of life in the ocean's midwater. Usually, specimens are collected in nets. Removed from their natural environment, their lifeless – often damaged – bodies are then preserved in jars.

These stunning images, however, reveal the amazing daily lives of the interior of the ocean, says Jon Copley, professor of ocean exploration at Southampton University in the UK. "Having photographic evidence of these animals is important because they're rarely seen in their natural habitat. Traditionally specimens of mid-water animals like these are collected in nets, which don't preserve the intricate structures that you can see in a photo."

In December 2018 – at just 19 years old – Cai embarked on her first ever blackwater dive in Batangas Bay, Philippines.

In the water, colour disappears very fast as you descend, says Cai. "You have to get very close to the subject if you want to capture a good image. You want to be relatively still, even as they move around. And sometimes you find a subject, you get close to it, and then it starts to swim. Then you just have to chase it."

Hyper-focused on photographing her first deep ocean species, Cai swam away from the dive boat and her dive guide who was in the water with her. This is when she captured the image of a wunderpus octopus (seen above). As an adult this wunderpus will have zebra-like stripes, but in its juvenile stage, says Cai, its colour cells have not yet developed. "Almost transparent, it can blend in with the empty dark space."

Cai used three bright lights to capture this image, which also attracted all manner of zooplankton – larval shrimps, crabs and worms – to join in the fun. "There's a huge diversity of life here. It's like a festival."

Suddenly, though, Cai realised she had swum so far from the boat that she could no longer see its lights. Alone in the darkness, she turned around in the water – and saw nothing. "I turned off all my lights: my camera light, my hunting light." She hoped this would allow her to detect the obscure light of the boat in the........

© BBC