Experience: I lived underwater for 100 days

My stay in Jules’ Undersea Lodge started in March 2023. The habitat, secured to the bed of a 30ft-deep lagoon in Key Largo, Florida, wasn’t the most comfortable hotel I’ve spent time in, but then I wasn’t there for a holiday. I’m a biomedical researcher and I was there as part of a scientific mission called Project Neptune 100.

The main aim was to research the mental and physical impact on the human body of living in increased atmospheric pressure – 70% higher than at the surface. It was also to study what happens when you leave someone alone in a confined environment for 100 days. The data might have all manner of applications – for future missions to Mars, for example.

Having spent 28 years as a naval diver before retraining, this kind of environment wasn’t new to me, so when the opportunity arose, I was happy to be a human guinea pig. My girlfriend’s ultimatum: “You can have 100 days, but not a minute longer.”

To reach the lodge, I had to scuba dive to the bottom of the lagoon. It was accessed from underneath through a “moon pool”, via which food would be delivered by a diver using a sealed plastic case. This central wet room also housed a small toilet and shower. On either side, a couple of 2m x 6m tubes contained the sleeping quarters and a kitchen-living room.

Each day I rose at 5am, did push-ups and a workout using resistance bands, had coffee and breakfast, then carried out a range of biomedical engineering experiments on myself throughout the day, such as checking my heart and brain, blood, urine and saliva. At 9pm I’d meditate, then have eight hours of sleep filled with vivid dreams.

There was room to stand in the lodge, but I cracked my head repeatedly on a screw sticking down from the ceiling. After a couple of months, that stopped – I’d shrunk by three-quarters of an inch. Whereas astronauts are in low gravity and get taller over time, aquanauts’ spines become compressed.

Initially, I had some concerns about how the isolation and lack of sunlight might affect me, but I took vitamin D supplements and had weekly sessions with a psychologist. I did miss more tactile interactions with friends and family, though my 80-year-old mother took a scuba lesson to pay me a visit. Otherwise, I had at least one visitor each week – marine scientists, microbiologists, astronauts and doctors – and continued to teach my biomedical engineering class via Zoom.

The lagoon is used for diving lessons and I’d always pause to acknowledge the children outside. Even after catching a sickness bug, I crawled over from the bucket I’d been throwing up in to high-five a kid swimming past.

Another regular visitor was a lobster I called Fred. When Fred once passed by doing a strange undulating motion, I pulled on my scuba gear and swam after him, but found just his empty shell and a little pink, gelatinous thing skulking away from it. I’d just watched a lobster moult underwater. How often do people get to see that?

Early on, I also spotted a 1.5m nurse shark, circling at some distance. Over the weeks, she gradually got closer and closer. Seventy-five days in (just after I’d beaten the world record for staying underwater without depressurisation), I found her sleeping on the step at the entrance to the moon pool. I had to move her out of the way to get into the water to exercise. She’d seen me every day and finally accepted me as part of her environment.

Over the mission, I experienced notable improvements in health. Tests revealed that collagen and stem cell production in my body had increased, suggesting a potential slowing down of the effects of ageing. I doubled my REM sleep, waking up refreshed and alert every morning. Thanks to the increase in my metabolism, I lost 23lb and 100 points on my cholesterol.

The only miserable thing was cracking a tooth on day 12, which I had to endure for the remaining 88. Feeling the sun on my face again and getting my tooth fixed were the most satisfying aspects of returning to dry land.

Back at normal atmospheric pressure, I spent a little time each day hanging upside down. After seven or eight months, I was 6ft 1in again.

As told to Chris Broughton

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