Black Water Diving
Written by Roy Kittrell 20 December 2023.
It is 6pm in Batangas in the Philippines. The sun is starting to set; the sky turns a variety of beautiful colours, and gradually our surroundings begin to darken. In the ocean directly in front of the Anilao Photo Academy, an incredible natural phenomenon known as the Diel Vertical Migration is about to take place.
Billions upon billions of tiny zooplankton, a collective term organisms classified as ‘animals’ (as opposed to plants, fungi and bacteria) that normally live in the deep mesopelagic oceanic zones up to 1000m depth, entirely out of reach of us divers, migrate upwards to the epipelagic zone to feed. To the zooplankton, relative to their tiny size, it’s the equivalent to swimming the height of Mount Everest, multiplied by 3. It’s the largest migration of organisms anywhere on earth, and it happens every single day in the ocean, hence the ‘Diel’ in its name. So large and so dense is this cloud of organisms, that they appear on sonar for ships as a false ocean bottom and have to be corrected for.
At this point, these animals are now close enough to the surface that we can dive and swim among them. This relatively new and exciting form of diving is known as Blackwater diving, and it’s gradually becoming more common as an offering of dive centers around SE Asia. In Dec of 2023, after many years of thinking, planning, and building up the necessary courage to do so, I was finally going to get my chance to try it for the first time.
The process is simple; you suit up in your wetsuit, get in a boat, and go out towards open ocean, or in our case the center of the Batangas bay, which is deep enough that the zooplankton are present. You drop a long rope tied to powerful lights at regular depths of 5, 10, 15 and 20 metres and wait for it to attract life.
Looking down into the pitch-black water, I could see the bottom of the rope and the tiny organisms already swimming around it. After 30mins or so we got the all-clear to enter the water and descend.
The water was thankfully very calm, with hardly a ripple on the surface of the water. My buoyancy had been carefully trained over the last few days doing normal reef dives, so at around 5m I was perfectly weightless and floating over what looked like a black, bottomless abyss. Around me, tiny white particulate matter floated without moving, giving the odd sensation of floating through a galaxy of tiny stars. My eyes began to adjust, and eventually I started to see the movement of small creatures through the water column.
One of the benefits of diving in almost total darkness is that you can see subtle bioluminescence of thousands of creatures. Comb Jellies, around the size of my fist, and normally only found in the deep oceans at depths as far as 7000m, swam around me, with a dazzling array of colours throughout their body. They are part of the phylum Ctenophora; and move through the water using tiny arms known as cilia, the largest creatures to use this method. Like tiny LED panels they looked like strange alien spaceships collecting detritus. Bioluminescence also came from other areas that I couldn’t identify, on my third blackwater dive the entire bottom of the diving area was covered by tiny blue blinking lights, that would at points entirely surround me, one of the most amazing experiences I have ever had diving.
I spot another transparent creature moving in an undulating rhythmic motion, very much like a small tadpole, and I start shooting pictures with my camera. After some further research later, I was delighted to realise I had seen my first Larvacean, a type of Tunicate that is entirely pelagic and has some remarkable abilities. These animals (they are in fact in the phylum Chordata) can build a large and very complex structure around their bodies made of mucus, which filters out large inedible particles from the water and channels the smaller edible parts to their mouths. Every few hours, they discard the mucus web, which is full of particulate matter, and it sinks quickly to the seafloor. En masse, this process by billions of larvaceans has recently been identified as an important method of carbon sequestration in the ocean, and it’s even thought that these animals will help to lower the amount of microplastics found in the sea.
If the reef we see during our day dives is the domain of the Corals, the Phylum Cnidaria, the open ocean would appear to be the domain of the Tunicates, also known as Salps, of the Phylum Tunicata. There were many hundreds of them swimming about us, sometimes individually, and sometimes as part of longer chains. The most impressive of all of these however, were the gigantic pyrosomes, sometimes as long as 15m and maybe half a metre in diameter, that would sometimes float past me. They are a colonial group of tunicates all living together as a colonial organism, and when you looked closer you could see the individual organisms quietly pumping water and filter feeding. They are rarely seen during the day, certainly this was my first time seeing them. It’s hard to articulate the feeling of taking pictures of tiny centimetre sized organisms, and then looking up to see a huge pyrosome suddenly appearing next to you and moving past silently!
I am not the only creature here that is aware of the tunicates. Phronima, an amazing type of amphipod around 2-3cm long, preys upon these salps and attacks their interiors to create a safe place to lay their eggs. They are one of the few kinds of crustacean that are classified as parasites, and it was amazing to see this legendary blackwater animal.
Not all life here stays in the open ocean as a planktonic organism. Many reef (i.e. ocean bottom dwelling, or ‘benthic’) animals form part of the diel vertical migration during their larval stages before ‘settling’ back to the reef. I saw many familiar reef dwellers, seahorses, octopus, and on one of my dives I was even lucky enough to see a larval Wunderpus, one of the highly prized subjects for Blackwater photography. On another of the dives, my guide pointed to a tiny pea-sized, bloated and very unremarkable looking fish that turned out to be a juvenile angler fish, the kind normally found living on the abyssal plains of the ocean floor at depths up to 2500m
On my second dive I was even lucky enough to see a curious juvenile Harlequin Ghost Pipefish (Solenostomus paradoxus), one of my favourite animals. I followed it for a while firing off some pictures, until I suddenly looked up and realised I was alone, in total darkness at a depth of 18m! One of the reasons that blackwater is generally reserved for more experienced divers is the lack of visual reference, and it is certainly easy to get disoriented and become lost if you are not careful. The key as with all diving is to stop, remain calm, watch your bubbles to see which way is up, and then to find your way back to the dive lights with the help of your guide.
The interaction between animals can sometimes be surprising here. With the almost total lack of any kind of shelter, juvenile reef fish will use almost anything they can to gain cover, from floating tree branches or trash,to jellyfish! The juvenile jackfish appears to be resistant to jellyfish stings, and we saw one pushing a jellyfish, face first, all over the diving area. The jellyfish deters predators from what would otherwise be a quick, easy and tasty meal.
Many creatures are transparent in the Diel Vertical Migration, for the obvious reason that it helps to conceal them from predators. But it also leads to some absolutely amazing looking photography as well. A normally quite boring and uninteresting subject for most reef photographers, the humble flounder is an amazing subject in it’s juvenile stage, lighting up like it was in an X-Ray scan, and even showing it’s internal skeleton and organs.
I had wondered before this trip whether I would find the whole experience scary or even terrifying, and I have to say that there were certainly points where I was a little unnerved, but overall I mostly just felt euphoric at finding something entirely fresh and new in a hobby I have been enjoying for years. In fact, back at the dive centre I asked some of the other more experienced BW divers about their most scary experiences doing BW, and nothing of any real danger had ever happened to anyone. The closest thing he could think of was the time that a whale shark appeared out of the black to come check out the lights, which I can imagine would be quite the experience to have on a blackwater dive!
For anyone looking for a new and fascinating look into our oceans, to have the ability to see a critical part of the reef lifecycle, to feel what it’s like to be in a truly alien environment, I highly recommend trying it out should you ever get the chance.
-Roy Kittrell is an avid naturalist and underwater photographer, his work can be found on Instagram @roythedivebro