The deep oceans contain marine species that can easily be mistaken for aliens. Fish, cephalopods, coral, worms, and crustaceans have evolved extraordinary adaptations to live in extreme conditions. The region of the ocean these organisms live in is known as the bathyal (1000-4000 meters below the ocean surface) and abyssal zone (greater than 4000 meters). Immense pressure, low oxygen, extreme cold, and limited light and food are several of the challenges these organisms face in these extreme environments. They are also what make these species so allusive to researchers. However, the recent advances in technology of remotely operated vehicles had allowed for scientists to discover new species and observe their behaviors in their natural environment. Their unique adaptations and behaviors are what motivate researchers to devote many hours and resources to the study of these peculiar creatures.
|The Blob Sculpin (Psychrolutes phrictus)|
is a good example of a "globular" body shape
The increased pressure at which these animals live also affects them at at the cellular level. Pressure decreases the fluidity of membranes as the molecules are crammed together. Proteins that are functional at normal pressures are denatured and not functional at high pressures. Therefore, deep-sea organisms have a greater proportion of unsaturated fatty acids, which increases membrane fluidity, than shallow-water organisms and have proteins that are adapted to function at extremely high pressures.
Another challenge bathyal or abyssal animals face is the scarcity of food and oxygen. Most animals have adapted to function at extremely low metabolic rates. Some have also evolved unique characteristics to increase their efficiency in capturing prey. Most predators use the sit-and-wait technique and have an upward-turned mouth containing long teeth.
|The Fangtooth (Anoplogaster cornuta) has the largest teeth proportional to body size than any fish in the ocean|
An additional adaptation the angler fish has evolved aids with reproduction. Because the bathyal and abyssal zones are so vast, finding a mate can be extremely difficult. Female anglerfish are much larger and more developed compared to males. When a male encounters a female, it will bite onto the underbelly of the female and remain attached for life (talk about a clinger). Eventually the male will fuse with the female. They will share a common circulatory system and his sensory organs will degenerate, until he is nothing more than a sack of sperm. This allows the female anglerfish to reproduce whenever she wants, without having to find a mate.
|A female anglerfish with two males attached to her underbelly|
A notable adaptation to improve vision in the darkness of the ocean is the tubular eyes of the barreleye fish. Its tubular eyes are extremely efficient for collecting any available light and are contained within the fishes transparent head. Usually its eyes are maintained in an upward facing position so it can look for food to steal from jellies, where its transparent head is useful for protecting these sensitive organs from being stung by tentacles. However, recently recearchers have discovered that the barreleye has the ability to rotate its eyes facing forward, allowing its moth to be in its field of vision.
|The Barreleye (Macropinna microstoma) contains tubular eyes (green spheres) inside its transparent head. The dark circles above its mouth, which resemble eyes, are actually its olfactory organs|
|The Giant Squid (Architeuthis sp.) caught by researchers off the Ogasawara Islands, Japan|
Cowles, D.L. and J.J. Childress. 1995. Aerobic metabolism of the anglerfish Melanocetus johnsoni, a deep-pelagic marine sit-and-wait predator. Deep-Sea Research Part I 42(9): 1631-1638.
Lundsten, L., S.B. Johnson, G.M. Cailliet, A.P. DeVogelaere, and D. A. Clague. 2012. Morphological, molecular, and in situ behavioral observations of the rare deep-sea anglerfish Chaunacops coloratus (Garman, 1899), order Lophiiformes, in the eastern North Pacific. Deep-Sea Research Part I 68: 46-53.
McClain, C.R., A.G. Boyer, and G. Rosenberg. 2006. The island rule and the evolution of body size in the deep sea. Journal of Biogeography 33: 1578-1584.
Robison, B.H. and K.R. Reisenbichler. 2008. Macropinna microstoma and the paradox of its tubular eyes. Copeia 4: 780-784.
Wharton D.A. 2004. Life at the Limits Organisms in Extreme Environments. Cambridge University Press. Cambridge, United Kindom.