Underwater photography and Ocean Exploration by Alexander Semenov

An amazing number of interesting things goes on underwater. For a marine biologist, it is like a huge book full of wonderful stories, whose pages you can turn by diving into different seas and oceans and discovering new things. Every dive and deepwater exploration are like poking a haystack with the tiniest of needles – the diver is the needle since he dives into a vast globe of water teeming with life and bumps into just a few of the inhabitants. The World Ocean is a living system of unimaginable scale: the oceans take up 71% of the surface of our planet and life is dispersed in the whole volume, not just the surface.

All the exploration of the oceans, including divers, deep water robots, and manned submarines is actually nearly negligible. During the last 2000 years we have discovered a little more than 236 000 species of marine organisms, and according to scientists’ estimates, that is only 8-10% of what really lives in the oceans. This means, that somewhere in the depths there are 2-3 million species that have never been seen by human eyes. Ever. We do not even know what they might look like!

The World Ocean is as close as you can get to outer space without leaving Earth. It’s an entirely different universe, nothing like the life we have on land. And while people dream about alien life forms from other planets, there is another universe right here, closer than anyone expects. As a marine biologist and underwater photographer, I have been studying and documenting this world for more than 10 years, organizing expeditions to the far-off corners of the planet, spending days and weeks under the polar ice, giving lectures, teaching classes at schools, writing books and making movies with a whole team of great people involved in my own project Aquatilis.

Anthozoa Pictured above

Actinia is a large group of sedentary cnidarians. These coral polyps are usually large solitary animals that attach themselves to solid substrates with their powerful feet. However, some Actinia transitioned to a burrowing lifestyle during their evolution and have no special attachment organs. These creatures have a cylindrical body with an oral disc at the top, which has a slit-like mouth surrounded by numerous stinging tentacles. Like other cnidarians, they are predators and feed on zooplankton, small crustaceans, polychaetes, fish and even jellyfish. Actinia have no internal skeleton. Instead, their shape is held together by the muscular walls of their bodies and their intestine cavity, which they can completely isolate from the surrounding environment by simply closing their mouths. When an Actinia closes its mouth, the water that remains inside acts as a hydroskeleton, shaping and toning the entire body. The Actinia stretch, shrink, move, burrow and bend thanks to their hydroskeleton and muscles which work in unison.

There are over 1,000 species of Actinia in the oceans, and they are very widespread, however, most of them live in tropical and subtropical waters. But you can find a wide range of fascinating and beautiful Actinia in Arctic seas as well. Thickets of Actinia often look like colourful meadows filled with alien flowers. Nevertheless, in the cold seas, you are more likely to encounter dense settlements of just one biological species, which can still cover entire underwater cliffs or multiple square kilometres of the seafloor.

Tunicata Pictured Above

Tunicates are marine invertebrates, members of the subphylum Tunicata, which is part of the Chordata, a phylum which includes fish, amphibians, reptiles, birds, and us, mammals. Some tunicates live as solitary individuals, but others replicate by budding and become colonies. They are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as syphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent (or inhalant) syphon and expel the filtered water through the excurrent (or exhalant) syphon.

The tunicates are divided into three classes: Ascidiacea (ascidians, or sea squirts), Appendicularia, and Thaliacea. Ascidians are largely benthic animals. They often form colonies, comprising a few to many individuals, which reach up to two metres in length. Solitary forms range from one millimetre to over 20 centimetres in length. The adult appendicularian resembles the tadpole larva of other tunicates. The body is enveloped in a “house,” with which the animal nets food. Small, usually less than five millimetres in length, including the tail, and simple, appendicularians do not form colonies. They spend their entire lives in the open sea. The thaliaceans (pyrosomes, doliolids, and salps) are also pelagic. Their structure suggests that they are ascidians modified in adaptation to conditions in open water. Pyrosomes form long, tubular colonies. Doliolids and salps occur both as solitary individuals and as chains.

All Images Alexander Semenov