She took the photo in Batangas Bay in the Philippines in 2020, following the eruption of the Taal volcano.
Cai remembers the serenity of being in the sea following the natural disaster, and said winning Ocean Photographer of the Year 2023 with her photo came as a surprise.
"That was totally unexpected because this is actually my first time to ever enter a competition," she told AAP.
The photo is part of a world-first exhibition at the Australian National Maritime Museum in Sydney, featuring more than 100 images from the world's best ocean photographers.
Cai said that on the night she took the photo, the water was like swimming in porridge, with almost zero visibility due to stirred-up sediment.
Just before midnight, she spotted the female paper nautilus, about the size of a coin, taking a ride on a drifting wooden stick.
When she pressed the shutter, particles of sediment reflected the light from her torch to create a snowflake-like effect.
While most photographers light their shots to remove small particles such as these, Cai intentionally incorporated them, as a reminder that tiny organisms are an integral part of the marine environment.
The paper nautilus is a unique type of octopus because it can grow a shell, which it holds on to using suckers on its tentacles.
"They just like hold it like a hat and put it on their head... it's just so cute," Cai said.
Also known as argonauts, they can swim but mostly choose not to, preferring to catch a ride on jellyfish or sticks, Â even pieces of plastic.
Cai grew up in Chongqing in inland China, and has just finished graduate studies in biology in the US, where she became interested in deep ocean creatures.
When she learnt about the vertical migration of zooplankton up and down the ocean column, she realised she didn't need an expensive submersible to see the creatures that live several kilometres beneath the sea surface.
"I can just wait at the surface at night and the deep sea organisms will come to me - wow!" Cai said.
"I feel like that is the closest connection I can build with the deep sea."
Cai now specialises in macro and blackwater photography, and finds diving in complete darkness a meditative experience.
"I feel it's like floating around in outer space, because you cannot see the bottom and around you is 360 degrees of darkness," she said.
The exhibition opens on Friday.
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