It is like that life on our planet began in the oceans. As much more of the Earth is covered with water than with land, and the sea can be thousands of metres deep, there is simply more space for living things in the oceans. However, the conditions that they experience there are not so varied, so there are fewer different species than there are on land. Well over 90% of the living things that thrive in the oceans are found in the fairly shallow waters around the continents. However, scientists have found that there is life even in the deepest oceans, although it is not easy to study wildlife in such remote areas.
The deep sea is an extremely harsh environment. It is dark, below 200m the light levels are too low for photosynthesis (the twilight zone), and not a glimmer of sunlight remains beyond 1,000m (the midnight zone). The water is very cold (37-50oF/3-10oC) and consequently has low levels of oxygen. The pressure at a depth of 2.5 miles is about 400 atmospheres, 400 times the pressure on the surface and equivalent to half a tonne per square centimeter. The density of organisms is therefore low. 25% of the estimated 8,700,000 species on earth live in the ocean depths, and 91% of those have yet to be discovered, described and catalogued (CoML). Many of these could potentially hold cures and new treatments for cancer, arthritis and other diseases.
The organisms of the deep sea are truly amazing and extraordinary, with every journey down uncovering more of the mysteries. This month a study published in Proceedings B of the Royal Society described a new species of deep-water acorn worms found 2,700m deep near the Mid-Atlantic Ridge with extremely long “lips” to help them capture prey in a habitat deficient of food.
Living in an environment where food is scarce, organisms need to be able to eat anything and everything that comes their way, the fangtooth (Anoplogaster cornuta) accomplishes this with its large cavernous mouth, and large dagger-like teeth (in fact, the teeth are so large is it difficult to close its mouth).
The deep sea anglerfish (Melanocytes Johnson) is aptly named for its elongated dorsal spine that extends forwards and lures prey towards its wide mouth and sharp teeth, with a glowing lure (containing bioluminescent symbiotic bacteria). The density of organisms in the deep sea is so low, that finding a mate in the right place at the right time can be quite a challenge. To avoid this potential problem, when they do meet, the male anglerfish will bite onto the female, their blood vessels fuse, and he will spend the rest of his life as a sperm producing appendage.
In the mesopelagic (twilight zone) where light levels are low, large eyes and reflective retinas are advantageous to make use of any vestiges of sunlight that penetrate down. Many deep sea fish possess photospheres (light producing organs), these aid in species identification, attracting food, or deterring predators. The lanternfish (small mesopelagic fish of the family Myctophidae) have photophores paired and concentrated in rows on their body and head in species-specific patterns. In some the pattern varies between males and females, with males having concentrations of photophores above the tail, and females below.
The Swimming Green Bomb (Swima bombiviridis) discovered in 2009, armed with “bombs” (shown by the arrow below) that glow a brilliant green when dropped, which they use as a distraction tactic to escape predators.
The Barrel Eye (Macropinna microstoma) is certainly a bizarre looking creature, with two green rotating eyes embedded in their transparent head. The dark “eye” like patches are in fact olfactory organs. Due to the lack of light even further below becomes a less important sense, and in many fish their eyes are considerably reduced, or even degenerate. Watch the video below to see this unique organism in action.
Winning the most awards for “ugliest fish” the Blowfish (Psychrolutes marcidus). This “grumpy”, “frowning” “blob” is able to withstand crushing pressure at 1,000m as its body is mostly a gelatinous mass with a density just less than water. It hovers with minimal energy expenditure just above the sea floor waiting for passing food particles.
