The Extreme Deep Ocean Environment and the Cookiecutter Shark

An environment is the conditions or surroundings in which an organism lives in. An extreme environment has extreme conditions outside of the "normal range" in which organisms usually survive. These extreme conditions could be things such as very high or very low temperatures, an absence of water or an abundance of water and very high levels of precipitation or very low levels of precipitation. An example of an extreme environment is the deep sea.

The sea covers around 71% of the Earth's surface and is sectioned into different ocean zones. The deep sea refers to all ocean zones more than 1,000m below the surface. These zones are; the Bathypelagic zone (Midnight Zone), the Abyssopelagic Zone (The Abyss) and the Hadalpelagic Zone (The Trenches). The different deep ocean zones all have varying extreme conditions that require the organisms which live within them to adapt.

One of the creatures that lives in the deep ocean is the Cookiecutter Shark, formerly known as the Cigar Shark. The Cookiecutter Shark lives between the Abyssal and Midnight zones and sometimes climbs to the Twilight Zone. The shark is a parasite which means that it "eats its prey in units of less than one" and is named after the cookie shaped bites it leaves on its prey.

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Describe the conditions of the deep ocean zone(s) that require special adaptations for survival of the marine organism.

I'm going to be outlining the conditions of the Midnight and Abyssal zones as these are the deep ocean zones in which my chosen organism lives.

Sunlight

In the Midnight and Abyssal zones there is no sunlight meaning that it is very dark. Most creatures in these zones are dark coloured. The dark colouring acts a camouflage against the darkness of the water to keep the creatures hidden from predators. This increases their chances of survival as it means they are less likely to be found and hunted by predators. Another adaptation that these creatures have is bioluminescence.

Bioluminescence is "the ability to produce light by physiological processes which helps the species lure prey." If deep sea creatures weren't bioluminescent they would be invisible to prey because of their dark camouflage and would therefore not be able to attract them. Bioluminescence can also serve to produce light in order for creatures to see.

Because there is no sunlight in these zones, there are no plants. This is because plants require sunlight to carry out photosynthesis and therefore live. It is extremely difficult to see anything in these deep ocean zones, therefore creatures which live in these zones must have adaptations for their eyes which allow them to see in the dark. Most deep sea creatures have very large eyes and reflective retinas to help them see. They are also helped through the use of bioluminescence as mentioned above.

Temperature

The Midnight and Abyssal zones have a temperature range of 2 - 4 degrees celsius. It is slightly warmer in the Midnight Zone compared to the Abyssal Zone as it is closer to the surface of the water and is therefore closer to sunlight which provides warmth. Most animals in the deep ocean zones travel very slowly because their metabolism is slowed down by the cold temperatures meaning they can't get as much energy as fast as some other creatures in the warmer ocean zones (3). Some animals also have fat to stay warm against the very cold conditions.

Pressure

The pressure of the Abyssal Zone can reach 11,000 psi at times which means that the bodies of the creatures which live there need to adapt so they don't become crushed under the pressure. Most deep sea creatures are made up of liquids that are not easily compressed meaning that they are able to survive under immense pressure.

These creatures also have strong bones so that they are not crushed due to the pressure. The pressure is so large because there is tonnes of water pushing down on the organisms which live within the deep ocean. The deeper the ocean zone, the more pressure there is due to the increased weight from above.

Describe the adaptations that enable the chosen marine organism(s) to survive in the deep ocean zone(s).

Behavioural adaptations

The Cookiecutter Shark lives between different ocean zones depending on the time of day. During the day, Cookiecutter Sharks stay around 1,000 m - 3,500 m below the surface in the Midnight and Abyssal zones. At night they climb to around 300 m below the surface in the Twilight Zone. The sharks move to shallower waters at night in order to feed. They do this because the shallower ocean zones such as the Twilight Zone, are home to the larger mammals which the Cookiecutter Sharks usually feed on. These include dolphins, whales, tuna and other species of sharks.

Structural adaptations

Cookiecutter shark is a grey/brown colour with a dark ring around it's gill area and a lighter coloured belly. This adaptation allows the Cookiecutter Shark to remain camouflaged in the darkness of the deep sea environment. Because the shark is camouflaged it means that it can remain hidden from larger predators. This increases the shark's chances of survival.

The Cookiecutter Shark is also bioluminescent in order to lure it's prey. The light from the shark's belly attracts larger fish which the Cookiecutter Shark feed on. The dark coloured ring on the throat of the shark, against the glow of the underside of the shark's body, is thought to make the Cookiecutter Shark look like a small fish when viewed from below.

The larger prey see this and move in to feed on the seemingly small and harmless fish. This is when the Cookiecutter Shark turns from prey to predator and feeds on the larger creature by leaving cookie cutter shaped holes on the creature's body.

The Cookiecutter Shark feeds on larger sea creatures by latching on to them with it's smaller top teeth while cutting the flesh with it's large bottom teeth. The shark spins its body to rip the flesh from it's prey leaving a cookie cutter shaped hole on its body. These bites are not fatal to the prey, but they provide enough nutrition for the Cookiecutter Shark.

Because the bites are not fatal and the shark only eats a small part of its prey, they are classified as a kind of parasite. The Cookiecutter shark has adapted to losing all of it's teeth at once as opposed to having only a few fall out a time like other sharks. The teeth are then digested and are thought to increase the levels of calcium in the shark's body which helps keep the shark's bones strong. This is an effective adaptation because it makes sure the shark's bones are strong enough to withstand the immense pressure of the deep sea environment.

In order to sea in the dark of the deep ocean, the Cookiecutter Shark has very large eyes on the side of it's head.

Physiological adaptations

The Cookiecutter Shark has an oily liver that is larger compared to the liver of similar sharks. It's large liver makes up around 35% of its total body mass.(1) The Cookiecutter's liver has low density oils which makes the shark able to float in the same place as opposed to sinking to the bottom.

This makes the sharks "neutrally buoyant" meaning they don't float up or down. This allows the shark to save energy because it has no need to constantly swim to avoid sinking. This is good because in the Abyssal and Midnight zones there is not very much food available meaning that energy is very precious and should be saved wherever possible.

The adaptations of the liver can also help the shark dive to greater depths. This would be very useful to the Cookiecutter Shark when swimming back down to the Midnight and Abyssal zones after feeding in the Twilight Zone.

Explain in detail and analyse how these adaptations work together to allow the marine organism to survive in this extreme environment.

In order for the Cookiecutter Shark to survive in this extreme environment, it must have adaptations to withstand the pressure. Two adaptations that work together to do this are; the shark's teeth falling out and the density/size of the liver. The density and size of the liver of the Cookiecutter Shark is a very crucial part of being able to withstand the pressure of the deep ocean.

The oil in the liver of the shark is very low density and not easily compressed(3), which combined with the large size of the liver, allows the shark to be able to withstand the immense pressure. As mentioned previously, it is thought that Cookiecutter Sharks lose their bottom teeth and then swallow them in order to increase calcium levels.

This increased amount of calcium helps to make the shark's bones stronger meaning that they are less likely to break under pressure. If this didn't happen, the levels of calcium that the shark has would be lower and it's bones would be brittle and easily crushed under the weight and pressure of the deep ocean. These two adaptations both work together to help the Cookiecutter Shark to survive in the Midnight and Abyssal zones.

Another set of adaptations that work together to help the Cookiecutter Shark survive in the deep ocean environment are; bioluminescence, camouflage and movement between ocean zones. Because the Cookiecutter Shark lives in such a dark environment it needs to be seen in order to attract prey. The shark does this by using bioluminescence. The underside of the shark lights up against the darkness of the ocean to be seen from below by potential prey.

The dark colouring of the shark does the opposite for the shark and keeps it camouflaged. This allows the shark to hide from predators and stay hidden when it moves from the deeper ocean zones to the Twilight Zone during the night. The colour of the shark also makes it seem small when viewed from below by prey. This paired with the bioluminescence fools prey into swimming closer to the shark in the hopes of eating it. When daylight nears, the Cookiecutter Shark then descends back to the Midnight and Abyssal zones where it remains hidden due to its camouflage.

Explain in detail anything else that would be relevant to the organism's survival such as how the adaptations allow the marine organism to coexist with other marine organisms in the same ocean zone(s).

The adaptation that allows the Cookiecutter Shark to coexist with other marine organisms is the teeth of the shark. This is because the Cookiecutter Shark is a parasite. This means that the shark eats small parts from prey as opposed to eating the entire organism. The shark takes small cookie shaped bites of flesh from the bodies of its prey. This leaves the prey injured but not fatally injured meaning it can live on and recover from the Cookiecutter attack.

When I was researching I found it was very difficult to find information about the adaptations of the Cookiecutter Shark that help it coexist with other marine organisms. This means that the Cookiecutter Shark is quite an independent creature and more research needs to be done about the nature and behaviour of this shark.

Conclusion

The deep ocean is the largest of many extreme environments on Earth and is home to very many different types of organisms all with their own sets of adaptations which work together to help them survive and coexist with other organisms. The Cookiecutter Shark is one of these deep ocean creatures and although I was able to research enough to write a report about it, more research needs to be done about this mysterious creature.

Bibliography

• "Deep Sea: Cookiecutter Shark - Elasmo-research." http://www.elasmo-research.org/education/ecology/deepsea-cookiecutter.htm. Accessed 6 Jun. 2018.
• "Interesting Facts About the Abyssal Zone That'll Startle ... - ScienceStruck." https://sciencestruck.com/interesting-facts-about-abyssal-zone. Accessed 5 Jun. 2018.
• "How Deep Sea Creatures Survive | Water Temperature Ocean ... - Fiboni." 15 Mar. 2013, http://www.fiboni.com/2013/03/the-survival-strategies-of-deep-sea-creatures/. Accessed 6 Jun. 2018.
• "Cookiecutter Sharks, Isistius brasiliensis ~ MarineBio.org." http://marinebio.org/species.asp?id=491. Accessed 5 Jun. 2018.
• "The Cookiecutter Shark Is A Weird Species Of Shark - Shark Sider." https://www.sharksider.com/cookiecutter-shark/. Accessed 13 Jun. 2018.

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