Seeing in the Dark - Or ?...

Have You ever wandered - how is it possible for creatures of the deep to see ? Do they even “see”, - or do they find their ways differently than we might imagine ?

In this “Editorial” we will take a look at some of the beings that live in the deep, dark Ocean, and discover if they stumble around in the dark - or if they are highly evolved in ways that enables them to see in the dark.

Photo by Lukas Robertson

Pitch black...

- That is how we might imagine humans experience in the deep Ocean when submerged in a submarine… But is this how the deep sea inhabitants experience their home ?

One may think that life in the deep has no need for eyes - since the sunlight is not able to reach, leaving a world of darkness - but most deep sea animals have a quite good eye sight. A study, suggested that deep sea fish eyes were compatible with the eyesight of middle aged human beings.

https://phys.org/news/2014-11-deep-sea-fish-eyesight-similar.html


But as we know, humans are not equipped with night-vision… Neither are deep sea fish.

Yet, what makes the world of deep sea fish special, is that they do not need sunlight to see - instead they produce light themselves.

Photo by Darío Méndez

Sinking into the Ocean...

- The colors slowly begins to fade and it becomes darker the further down You dive.

Eventually sunlight “stoppes” reaching a level of approx. 1000 m - and the average depth of the Ocean is 4000 m, - leaving what we may imagine to be a dark world… But in the deep sea, many creatures lights up the harsh environment !

https://oceanservice.noaa.gov/facts/light_travel.html

Photo by Jack B

A study has shown that over 50 % of all deep sea creatures can produce light.

https://www.smithsonianmag.com/science-nature/bioluminescence-light-is-much-better-down-where-its-wetter-22988383/?no-ist


This type of light is called “Bioluminescence”. Bioluminescence is a quite complex chemical process in the animals body - it is explained in depth in the link below.

https://ocean.si.edu/ocean-life/fish/bioluminescence


What is very fascinating about this light creation, is how the animal that produces bioluminescence is able to control the process.

The animal is often able to control when to light up, how strong this light shall project, - some animals can even create bombs, that are able to explode into the face of a predator, allowing the animal to get away in a veil of light, - and the features continues !

Photo by Samuel Zeller

The Bioluminescence light is normally blue, which makes perfect sense since the intermediate wavelength of the blue color, enables this color to travel deepest into the Ocean. This also means that many deep sea animals are only able see the blue color tone. This is very practical since they no longer need to “spend energy” trying to detect colors that “does not exist in the deep”.


Yet, a paradox also exists in the deep Ocean, since the color yellow, and most weirdly - red is also known to be created by deep sea beings.


What makes this interesting ?

The first color to disappear when descending into the deep Ocean is red.

http://connieimboden.com/2013/12/the-science-of-color-underwater-2.html

Red color has a very long wavelength, which means the Ocean quickly “drowns” the color.

So, the fact that the color red can be found in the dark deep, produced by, for instance, the “Barbeled Dragonfish”, is quite spectacular - and not without reason !


Lighting up in the darkness, can be quite dangerous !

Producing light has many advantages - being able to “find” a mate in the dark, and to lure in food, by attracting / hypnotizing prey with the light etc. Yet, creating light is also a dangerous move to make, since this also brings attention, and attracts the potential threats and predators, that are willing to do whatever it takes to catch a snack.


This is the part where the red color bioluminescence comes in handy.

Since red color has very long wavelengths, it can even be a problem for humans to see the color, - and as mentioned, the Ocean normally absorbs the color. This combined with the fact that many deep sea beings has lost the ability to detect other colors than blue, since this is the most relevant and popular color of the deep, - the red color creates an almost secret society of deep sea creatures that “appreciates privacy.”

Photo by Will Turner

Many of the deep sea species creating red light, is species in the bottom part of the food chain, with many potential threats. Though, still they need to be able to catch prey, and find one another in the dark to create the next generation.

So this ability, to create red light, can be a great advantage !


Though, some animals of the deep, like the “Barbeled Dragonfish” mentioned earlier, has evolved, - and is in fact able to see both blue and red colors… Therefore, red light is not functioning completely as an invisible cloak in the deep Oceans.

https://www.nbcnews.com/science/science-news/dragon-fish-evolved-see-reds-blues-n45321


When talking about the deep sea and light, it would be strange to leave the most iconic deep sea fish out of the picture…. The Deep Sea Angler fish !

https://www.nationalgeographic.com/animals/fish/group/anglerfish/

Photo by "Spider Dog"

There are roughly around 200 different species of anglerfish in the Oceans, and most of them inhabits the deep sea.

Properly best known is the cartoon deep sea anglerfish from “Finding Nemo”. In the movie sequence, the cartoon anglerfish also lit´s up the dark Ocean with it´s almost “fishing-rod-look-a-like” antennae, or as it is called scientifically “the dorsal appendage”.


Yet, the male Anglerfish are not able to light up, since their main job is to find a female. The males are therefore equipped with sharp senses including great sight, for them to be able find a mate in the dark.

The female anglerfish, with the “glowing-features”, also has giant appetites ! Some anglerfish are actually able to lure in prey twice their size, and with their giant tooth-filled mouths catch and eat the prey, despite the size. These anglerfish often has the ability to stretch their stomachs, which are in fact “light-secured”. This light security makes sure that the prey that might be swallowed alive, will not be able to light signal for help though the stomach skin of the anglerfish, - quite smart and a brilliant case of evolution !


These are but few exampels of some of the inhabitants of the deep Ocean, - that has created methods to light up the dark, signal for partners and lure in prey.


So, the deep sea world is in fact not pitch black, - not even for human-submarine visitors.

Photo by Richard Hirajeta

Light can be found, produced by more that 50% of the deep sea inhabitants, creating a dim light universe of peculiarity - different from what we might imagine, - and highly fascinating !

By Blue Reporter, Naja Bertolt Jensen

If You are interested in more facts and informations about the deep sea, follow the links below :


How to Protect the Deep Sea

https://www.pewtrusts.org/en/research-and-analysis/fact-sheets/2018/12/how-to-protect-the-deep-sea


What We DON'T Know About the Deep Sea

https://ocean.si.edu/ecosystems/deep-sea/what-we-dont-know-about-deep-sea


Ten things you never knew about the ocean’s deepest places

https://theconversation.com/ten-things-you-never-knew-about-the-oceans-deepest-places-55172


10 BIZARRE FACTS ABOUT DEEP-SEA CREATURES

https://www.unbelievable-facts.com/2017/10/facts-about-deep-sea-creatures.html


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