Tom Iliffe only studies animals that live in the hardest-to-reach locations -- those weird colorless, sightless organisms that exist only in the world's deepest, darkest, underwater caves. As a biologist and a diver, he has been down to 460 feet below the ocean's surface and spelunked some of the world's most remote locations all while breathing through a dive regulator. Throughout his career, Iliffe has discovered 250 new species of marine and freshwater cavernicolous invertebrates, including 3 new orders, 7 new families and 50 new genera. He talked to us about how to find your way around a previously undiscovered cave without getting lost, how to swim through tiny cracks and crevices, and what it's like to grab samples of tiny nearly-invisible animals in the darkness of an underwater cave.
Why study caves?
First of all, it's like any form of basic research. You may set out just to learn how something works but you never know where the path is going to lead you. Some of the most exciting scientific discoveries that have taken place were because people were curious about a phenomenon and investigated.
So that's kind of the starting point. We have a totally unknown realm, we know nothing about it, this is a challenge, let's learn what's happening here. Not: "let's find something that has immediate commercial potential." Just because you start out at the bottom rung of the ladder, doesn't mean you can't end up making very important discoveries.
A lot of the most important discoveries that have ever been made have been by accident, by a fortuitous discovery. You don't have to have a rationale other than scientific curiosity.
That's to begin with.
But we have made some incredible discoveries in caves, those that from the beginning would have been unanticipated. For example, there's a type of very usual and rare crustacean that we discovered that lives only in deeper saltwater layers of certain caves, it's called Remipedia. It's not just a new species -- Remipedia is a new class of crustaceans. It's a totally unknown type of animal that had never been observed anywhere else on the planet.
Does that mean when you discover a new animal you get to name it?
What I do is I work with a number of other scientists like taxonomists, which are scientists that specialize in classifying and naming new forms of life. Because I work with a broad range of animals, it's' impossible for me to be an expert in everything. So I rely on a number of scientific collaborators from around the world. My job is to locate, collect, properly preserve, document, and photograph the animals we're finding and then to send them to specialists in one group of organisms or another at universities around the world.
So if you don't specialize how do you know when you've found something new?
I've been doing this long enough that I can pretty well tell when I see something whether it's ordinary or a type of animal we've never seen before. That's happened numerous times -- seeing something totally unlike anything I recognize. I get a strong hunch and generally they pay off, turning out to be correct.
You're one of the pioneers of cave diving research. How did you get started in such an uncommon field?
After I finished my PhD in 1977, my first job was as a research scientist at the Bermuda Biological Station. One of my hobbies had been exploring and diving in caves, but strictly as a hobby. I arrived in Bermuda to find that within a 15 minute ride from my house, there were well over 100 caves. When entering them, you don't have to go very far until you've reached sea level where there's a deep pool, a tidal pool, moving up and down with the ocean. So that implies there's some sort of connection with the sea.
I asked my boss: "Has anybody ever done any scientific studies of these caves?" And he said: "Yeah, a few years ago some people went out to four or five cave pools and didn't find a single thing and decided they were abiotic lifeless environments." That didn't seem logical to me, so I took it on as personal challenge.
When my friends and I started diving these caves, we found a layer of fresh or brackish water at the surface. But when you got 10 or 15 feet underwater, the water became fully marine. It was down in these deeper salty waters that there was a fantastic variety of organisms. The key to discovery in the caves was diving. You couldn't access these unique habitats in any other way.
So when we began diving, we found all sorts of strange, cave-adapted marine life. One, for example, I sent to a colleague who was an eminent curator at the Smithsonian Institution in Washington. He was an expert in all sorts of different crustaceans, his job was to classify rare crustaceans. So he'd seen a little bit of everything for the last 30 or 40 years. When I sent him these, he said: "I've never seen anything remotely like this."
Were you the only person researching caves as a diver at that time?
There were several other people independently who were doing some of the same sorts of things that I did. But it wasn't very common.
Part of the reason why is the technology. Cave diving is very different from open water diving. In open water, if you have problems with your gear, you simply swim up to the surface. In a cave you could be many hundreds or thousands of feet into the cave, not necessarily deep but a long way in with a rock ceiling over your head. You can't go straight up. You have to go back the way you came in. So you have to have air and know which way is the way back out.
Cave diving is very different from open water diving. In open water, if you have problems with your gear, you simply swim up to the surface.
There's a lot of specialized technology that's unique for cave diving. This was developed by accident analysis -- where people looked at why people died in caves, what did they do wrong and how can we prevent such tragic results? In Florida alone, there have been nearly 500 fatalities in underwater caves in early stage development. It was incredibly dangerous.
So there are many thousands of caves that have never been scientifically explored or investigated. Even in the caves we know, we find new organisms. We still need to study the ecology, behavior, and food webs in the caves. We don't fully know how animals live in these lightless, food poor, and oxygen depleted environments, what adaptations have happened to the nervous system, where the ability to detect chemicals in the water comes from. There's no light, so vision is out of the question. Most cave animals are blind and have no pigmentation. So as soon as they go out of the cave, they get picked off by other predators like fish or birds.
So when you go on a cave dive, what gear do you need to bring with you?
You first need to know where you're going to. The type of cave, size of passage and water depth are all going to play a role in the selection of equipment.
When cave diving started with normal open water divers, they had tanks on their backs. But because we need more air in caves, you carry significantly more. You need double tanks. How many hours' worth depends on the cave, your breathing rate and the water depth.
Sometimes I may do a recon dive ahead of time if i'm going to a remote spot. So I'm gonna stick my head in and look around a bit and see if I need to set up for a longer deeper dive.
But typically we use double tanks, either the standard aluminum tank that's used by most scuba divers or high volume steel tanks. They can either be worn on our back, manifolded together with two separate regulators, so if one fails, you can turn off that regulator and still have all the gas in both tanks. It's important to have redundant equipment, allowing for failure of one part that doesn't totally end in your extinction.
That's the way we started cave diving historically.
But then changes came about for several different reasons, either carrying two tanks to a far off cave is very heavy, or there were places in the caves that were cracks only 12 inches high but 8 or 10 feet wide so that you couldn't get through with tanks on your back. The solution to these problems involves using two single tanks, one under each arm, a technique called side-mount cave diving. It's very comfortable. It takes the weight off your back and you feel like almost like you have no equipment on.
A lot of cave divers now have switched over to diving side mount and that allows them to go through narrow slots and cracks. They're more accessible. The butt of the tank is clipped on near your waist and the valve where the regulator is up on your chest. So you can actually unclip your tank, swing it around 180 degrees, and push it through a small hole in front of you. That way you can squeeze through very tiny places that you wouldn't be able to get through otherwise.
Are there different rules for planning use of your air supply when you're diving in a cave?
This was also determined through accident analysis. You use no more than one-third of your air on your way in. At that point, you turn around and start back out. So you have one-third to get out and one-third left for handling emergencies. You never go further into the cave than one-third of your gas supply.
That's why we need two tanks; this provides not only extra air, but also redundancy. With one tank, you wouldn't get very far. So in theory, using only one third of your air, you have plenty left for exiting the cave. Unless there's a problem and you have to share gas with your buddy, or you've stirred up the sediment and you can't see your hand in front of your face so you have to follow the line on the way out. In either case, your breathing rate goes up. The faster you breathe, the more air you use, so you might not have enough gas to get out of the cave alive.
A third major type of cave diving makes use of closed-circuit rebreathers. The diving we've talked about so far is open circuit scuba that normal recreational divers use. Every time you exhale all of the gas from open circuit scuba is lost in the form of bubbles. You're continually working through your air supply until all the gas is gone.
But there's a system called closed-circuit system, and with that, all the gas that you exhale is recycled. It goes through a carbon dioxide scrubber in a canister on your back. Then either manually or automatically you add a little oxygen to maintain the appropriate oxygen partial pressure and you're breathing the gas over again. So you're recycling all your exhaled gas. With an open circuit system, I can stay down an hour or two depending on the depth. But with a rebreather, I can stay down six to eight hours and at any depth.
That's because with the open circuit, if your tank lasts an hour at the surface, it lasts a half an hour at 33 feet and 20 minutes at 66 feet, etc. Your available air supply gets progressively smaller, the deeper you go. But with a rebreather, the rate of gas consumption is based on how fast your body metabolizes oxygen such that the gas you have access to is the same at any depth.
It's also good because there are no bubbles so there's no disruption of the organisms we're trying to find or collect or study. With open circuit, there's a lot of noise from bubbles. It's very loud and noisy.
My longest dive on a rebreather has been about five hours. The good thing is if there's a problem or an emergency, the rebreather gives me more time to solve a problem -- so time isn't quite as critical.
Do you carry a light?
We always carry a minimum of three lights. Some divers carry more. Each light should be able to burn for the intended duration of the dive. We have a primary light, which is our brightest. Those burn four plus hours or more. They can either be HID, high intensity discharge bulbs, or some new LED bulbs that are very bright. You also have a separate battery pack on your waist or behind you clipped on your butt. The power cord comes out and you have the lamp itself in your hand.
Then you have at least two other smaller lights that also need to have a burn time equivalent to the duration of the dive.
Do you just wear the standard wetsuit?
Most of the caves I'm working in are in the tropics, it's warm but you're in for long time. Typically I wear a wetsuit, but if the water gets cold or the dives are very long, I'll switch to a dry suit. Just like a standard dive.
Do you ever worry about the animals you've never seen before being dangerous?
No, most are very small because caves lack light and photosynthesis so that typically food is scarce.
But every dive is a little bit different.
We may have to carry our gear for a mile or more into the jungle. We often times need to use a machete to hack our way through the jungle using a GPS to determine direction and distance to the cave. When we get to the site, the first thing we do is a site check to look around and see what the conditions are like. We were diving at a cenote cave pool in Mexico this summer where there were crocodiles in the water. We could see the nose of a crocodile sticking out of the water on the far side of the pool where we had to jump in to enter the cave. Fortunately, the crocodile was shy and didn't bother us.
How do you go about picking a cave to study?
Local knowledge is one of the biggest advantages in finding new caves. There's a large community of recreational exploration cave divers. They discover and map not because they're scientists but because they're explorers. They want to go to places that no human being has ever been. We talk to them and find out what they've found and what places sound potentially interesting to us. Often times we follow on their heels.
Other times we go to an area that no diver has ever been and we're the first. For example, we're doing work on the out islands in the Bahamas. We examine topographical maps and compare sites of potential interest to see out they appear in Google Earth. In this way, we are able to determine the latitude and longitude of potential sites. Then, with the GPS, we could hack our way through the jungle to begin our diving exploration.
It sounds exhausting.
I try and stay in good shape. When you're in the water and swimming a lot -- on an average dive we're in the water for 1.5 to 2 hours at least and that takes quite a bit of exertion. If you were to swim really fast, you'd be breathing rapidly and run out of gas in short order, but if you swim too slow, you never get anywhere, so there's an intermediate speed that helps you cover the maximum distance on the available air supply.
Do you ever feel nervous swimming into the dark unknown? Sounds scary to me!
I've been doing this for a long time so I'm calm before a dive. We're also very careful and conservative. If conditions get bad or we've reached our air supply or physical limit, it's better to turn around and come out a bit sooner than it is to stay until you have exceeded your safe limits.
Oftentimes if we're in a new system, on the first dive, we may not go as far as we can. Then for the next dive, we know quite a bit more about the system and can go farther. We work our way in slowly. When we get to a point where we've used one third of the gas in both tanks for penetration, the next dive we take three tanks.
When you have three tanks, you start off breathing from the additional stage tank that's clipped to your chest. When you've used one-third, you turn off the gas to that tank and you clip it to your guideline, which shows you which way to go in the caves. Then you still have your remaining two tanks that are still full. It's a bit harder to swim wearing three tanks, so you leave the third behind and pick it up on your way back out of the cave.
We can carry four, five, even six or more tanks if need be. The most I've taken though is five on one dive.
What was that dive like?
I have conducted a number of research projects in Bermuda over the years. The average depth of the underwater caves there is about 60 to 70 feet and there's a wide variety of rare and unusual animals that inhabit them. During the Ice Ages, 7,000 or more years ago, these caves were all dry and air-filled. So we wanted to know: where did the animals that now inhabit the caves live during the Ice Ages when so much water was taken from the oceans to form glaciers that sea level was down 300 feet or more?
On a NOAA Ocean Exploration funded project, we used high resolution multibeam sonar to make a map of the entire perimeter of the Bermuda island from depth between 200 and 600 feet. There's a near vertical cliff at those water depths. If, during the Ice Ages, you had a ship that sailed up to Bermuda, you'd have come upon enormous cliffs several hundred feet high completely surrounding the island.
So we wanted to see if there are caves deeper down on the sides of the Bermuda seamount where those animals could have lived when sea level was low. The first step was to create a detailed sonar map of the island's perimeter, extending a bit above and below where the seawater was during the Ice Ages. The second step was to go in with ROVs (Remotely Operated Vehicles) to have a look at potential cave entrances. Finally, the last step was to go and dive there ourselves.
Our deepest dive was 460 feet, a depth below the deepest point that sea level reached during the Ice Ages. We used closed circuit rebreathers providing trimix (a breathing mixture of helium, nitrogen and oxygen gas), but as emergency backup, we had bailout bottles of trimix and decompression gas in case our rebreather failed and we needed to switch to regular scuba to make a controlled ascent.
We were looking for cave entrances on the vertical wall at deeper depths by checking out potential sites we had discovered with our sonar map. Even at these depths, there was enough ambient light that we could see 100 feet or more in any direction. However, time was crucial, from the time we left the surface until we had to leave our deepest depth was a mere 15 minutes. That doesn't give you very long.
In contrast, our ascent took much longer -- an hour and a half or more to come up so that absorbed gas would come out of our tissues slowly, thus avoiding decompression sickness. Our first decompression stop was around 150 feet and then we had to stop at 10 foot increments on our way to the surface. Our last stop was at 20 feet and we had to stay there nearly an hour.
All this time, we were hanging on a line in open ocean, with no possibility to go to the surface until our decompression was completed.
Do you ever work inside caves that deep?
There are caves that go that deep or deeper. But typically the cave dives I do are 30 to 70 feet range. At most, around 200 feet.
How does the guideline system for finding your way back out of a cave work?
The guideline is the cave diver's lifeline, leading the diver out of the cave when lights fail, stirred up silt destroys visibility, or complex cave passages pose a threat of becoming lost. You tie off the guideline in open water outside the entrance to the cave so that even under the worst of circumstances, you can swim out of the cave and right up to the surface. A short distance inside the cave, the guideline is tied off the line again so no one can come along and tamper with the line outside the cave.
Do you ever leave someone outside for safety?
Sometimes helpers who assist in carrying your gear to the cave remain outside, but generally you don't need an extra safety diver. If there's a problem inside the cave, by the time they know about it, it's going be too late for them to do anything.
So after we tie off inside the entrance, we lay a series of straight segment of line. You look ahead down a tunnel ahead of you to identify a rock, stalagmite or other protrusion that you can wrap the line around creating a straight section of line under tension. It's not pulled as tight as a bowstring, but there's no slack. If there's slack and current, either the line could become untied or you could easily get entangled in it if you swim too close. The only way to get out might be to cut it and then there's the potential for it to snap back and then you're lost in the cave without a guideline.
So you keep it taught at all times.
What's the guideline made out of? Is it a special color?
The guideline is made of braided nylon. It's typically white, but in some caves where there are tourist divers you might find gold line that's thicker and gold or yellow in color. This helps you see that you're in a main tunnel and provides a navigation aid to relatively inexperienced divers.
In Mexico's extremely extensive cave systems, there may be tourists who are trained cave divers and the permanent gold line helps them to navigate and find their way around as opposed to the white line which is somewhat harder to see.
When you're laying down a line, the person who's going into the cave first has a reel and they're laying out line as they go. When they've used up all the line, they bring out a second reel or they turn the dive and the team heads out of the cave.
Do you take the line out with you afterwards?
Most explored caves have permanent guidelines that are left in them, but these permanent lines might not start for 200 feet or more away from the entrance. That's to keep novice divers from finding and following them too far into the cave. If novice divers see a line, there's a tendency to follow it and get into trouble.
You don't want to entice people in. Trained cave divers start their line outside the cave and then swim in until they connect their reel directly to the permanent line such that they always maintain a continuous guideline leading out of the cave.
The diver with the reel is always the farthest person into the cave, no matter whether they are heading in or out. They're the first person in and last person out. That way everybody else is closer to the entrance and on the guideline.
Do you ever swim away from the line?
Sometimes we move away from the guideline when we're sampling, but we always keep one person on the line to watch us and make sure that we can find our way back to the line and know which direction is out.
In any event, we never go farther from the line to a point where our buddy is no long visible.
And we never go anywhere alone.
So once you've laid your lines and you're ready to go about studying the cave, what are you looking for?
I'm doing something quite different than most other cave divers. I'm either looking for animals or trying to take measurements of the water quality. For example, I carry a Sonde, an electronic water quality analyzer. It can electronically measure the depth, water temperature, salinity, amount of dissolved oxygen, pH or acidity, and it can take measurements as frequently as once per second. All of this is recorded in memory in the instrument. So we program it before the dive and carry it with the sensors pointed forward into undisturbed water. At various places, I may swim up to the ceiling of the cave and then drop down diagonally to the deepest place on the floor and get a depth profile of the water quality.
Caves in Bermuda, Yucatan and other locations, there is a layer of fresh water at the top and then the halocline, the contact of fresh and seawater, and below that is seawater. In some caves, the halocline is a thin as a sheet of paper and you can plainly see it.
We take these measurements because we want to learn something about the water chemistry and where the animals are living. We also want to collect animals. Typically, I have clear glass or plastic containers that I fill with water at the surface and carry with me in a pouch. When I find an animal that I want to collect, I'll take out a tube or bottle and stick my finger in it to exchange the ambient water, prior to sampling. It is important to flush the water out because we're going to fill it with the same water that the animals have been living in. This allows captured animals to live for 24 hours or more in the collection bottle.
Why not just have air in the jar?
One time, I left a plastic tube in my chest pouch that I'd forgotten to fill it with water. The tube imploded at 90 feet and sounded like a gunshot.
As you go deeper and deeper, eventually you get to a depth where the pressure becomes too great and the tube is going to implode. One time, I left a plastic tube in my chest pouch that I'd forgotten to fill it with water. The tube imploded at 90 feet and sounded like a gunshot. It felt like somebody has pulled a gun and shot me in the chest. It scared the hell out of me.
Do you have to worry about pressure changes for the animals on the way back out?
Invertebrate animals don't have swim bladders like fish, which expand and kill the fish if they are brought up too fast. These are small crustaceans, shrimp or their relatives, so there's little to no difficulty with pressure differences.
Do you have to chase them around to catch them?
For sure. When you try to catch them, they'll jet away. So I come up and prod them so they'll swim away rapidly. I'll do that two or three times, until they use up their energy. The third or fourth time, they're out of gas and it's easier to scoop them up.
How many animals do you try and collect on a dive?
I make take up to 30 or 40 bottles, each of which is for an individual specimen. I write down on a slate what the depth is where I collected the animal. Then from the electronic water analyzer, I know if that's above or below the halocline and I'm able to say whether the animal is living in freshwater, saltwater, or in between.
How do you find them? Do you have to tease them out?
Most of the animals are living in the water column, so they're not crawling around on the bottom or on rocks. The undisturbed water in front of us when we head into the cave is air-clear, there are no particles or specs. When you shine your light around, the animals will reflect back your light. It looks like a little star in the water and as your light passes by the star goes out. Anytime you see something like that, you swim in to have a closer look. You can see incredibly tiny animals because there are no other suspended particles as there is in the ocean or elsewhere.
Unless you accidentally kick up something.
Yes, there is sand, sediment, and mud on the cave floor so that it is critical to have good buoyancy. You swim like you're flying, with a slightly head-down, feet-up attitude so that you're not disturbing the sediment. You want to have clear water so you can see the guideline without any difficulties. However, even with the best buoyancy techniques, your exhaust bubbles can knock silt off from ledges or the ceiling such that visibility declines over time.
How many dives have you done total?
Probably a couple thousand. I don't know the exact number since I stopping logging my dives for about a decade.
Have you ever had any major emergencies on a dive?
One time I was diving in a cave in Bermuda with some friends, a cave no one had ever been in before. There was a low silty tunnel in the cave. We swam through it for a couple hundred feet and it opened up into a large room. So we swam around the room, but there was no way out so I tied my line to the far wall and signaled to leave. I was the first in and going to be the last out.
We get back into the low tunnel and people had kicked up so much sediment that you couldn't see your hand in front of your face. I was swimming and sliding my hand along the guideline. But it was very slow going since you couldn't go faster than the people in front of you. After what seemed a significant period of time of blindly following the line, the ceiling came up and there was a bit of clear water. So I stuck my head up so that I could see the first guy at the beginning of the line. He had the guideline in his hand but it was a limp and loose, just hanging broken in front of him.
It turns out that he just thought he'd play a joke on us. He had some extra line he was holding up. We got a good shot of adrenaline there.
But we try and be very careful so safety, caution, care, and diving with a good team where you know people and you can rely on them to be cool and calm is absolutely critical to doing safe cave diving.
What types of people do you usually have on your dive team?
Each member of the team is an expert, specialized in a given task. We have one person like me doing the biology. Another has the Sonde and is doing water chemistry. We'll have a photographer to take pictures and document what we're seeing and doing. We'll have somebody specializing in mapping the caves. And we may have other team members who are specialists in deep diving if a part of the cave goes quite deep. We may have a special push team using dive scooters to see how far they can get into the system. My view is that each person in a team ultimately has their own job and is an expert at doing that.
For a project, we might include six or eight people, but we typically go in with dive teams of two or three. So a group goes in and half an hour later another team goes enters the cave. In that way, we get the most bang for the buck and get the most work done by having experts in the business.
Where else in the world have you studied caves besides Bermuda?
Right now I'm doing a lot of work in the Yucatan Peninsula in southern Mexico. I've also done quite a bit of work in the Bahamas, Bermuda, and Lanzarote, one of the Canary Islands, located in the Atlantic off the coast of North Africa. A couple years ago I had a National Geographic grant for a project on Christmas Island in the Indian Ocean.
I have a lot of places I'd like to go to on my wish list -- I'd like to do some collecting in some newly discovered caves in Turks and Caicos. I have a friend who's a cave diver in the Dominican Republic and has been discovering some amazing new caves there. He also has a project in Madagascar diving in caves where he has found giant lemur bones. I'd love to go over and dive in some of these caves to see what's living in them now.
Is there one cave you've dived in that stands out in your mind as being particularly interesting?
One of the strangest caves I have explored is in Lanzarote on the Canary Islands. Most of the caves we dive in are made of limestone, but this one is volcanic. It's a lava tube cave. It starts at the base of a volcano in the middle of the island, goes 3.5 miles down the side of the mountain to the coastline and then goes for a mile out to sea under the floor of the Atlantic. It's called the Atlantida Tunnel -- literally the tunnel to Atlantis.
It's incredible. It can be as much at 50-feet or more high and 30-feet wide. It's generally dark-walled but there's a lot of color in the lava. Half a mile in, as you're heading out to sea, you can see a dim white structure in the distance. As you get closer, you see it's a huge conical mountain of pure white sand. There's a small hole in the cave ceiling that connects to the seafloor above and sand has been dropping down through the hole to form a sand mountain that's 40-feet high and about 75- to 80-feet in diameter. Since it's a very small hole located half a mile out to sea, no one has ever been able to find it. When you're at the top and the sand mountain and look up in the hole and you can't see any light coming in from the ocean above.
The sand mountain contrasts against the sheer black walls of the caves – our dive lights reflecting off the crystal white loose carbonate sand seems to light up the whole chamber. There are also incredible views and unbelievable animals. Very few people are given permission to dive in this cave, because the main entrance on land is a prominent tourist attraction, the Jameos del Agua, such that you have to have permission from the local government. Also a number of animals in the cave are endangered species so that permission from the Spanish government is also required. Fortunately, a colleague of mine from a university in the Canary Islands has been of invaluable assistance in obtaining the necessary permits.
Many cave animals are only found in only one cave and nowhere else in the world. So if those caves are polluted or destroyed, the animals in them become extinct. For this reason, many of them are endangered species with the only way to protect them being to protect the caves they live in. As a result, a large part of my work now is to promote conservation initiatives for such unique subterranean fauna.
Not all science is done in a lab by guys in white coats staring into microscopes. Lots of discoveries require brave men and women to put their boots on the ground and get down and dirty in dangerous environments. Every month we'll profile one of these field scientists, tell you how they do their job, and explain the science behind what they do. If there's a scientist or field of science you're dying to hear more about shoot us an email or a tweet: erin at erinbiba dot com, @erinbiba