Colossal Depths Vs. Mega Adaptations: How much do we know about the world’s most extreme sharks?
Sharks are one of the most studied and recognised marine organisms on the planet – but how much do we actually know about the real monsters of the sea lurking below in the deepest, darkest and most adverse corners of the ocean?
Live long and prosper
The Greenland shark Somniosus microcephalus has been causing quite a frenzy in the media recently as they have been discovered to hold the secret to long life with an estimated life-span of 400 years. This makes them the longest living vertebrate on the planet. These slow moving sharks are native to Atlantic waters around Greenland, Canada and Iceland and have been found at an impressive depth of 1816m. Living in extreme cold temperatures (-1°C to 10°C) all year, they are the only true sub-arctic shark. Greenland shark flesh has been found to contain high levels of trimethylamine N-oxide (TMAO). This chemical which increases with depth is used to regulate osmotic pressure and act as a natural antifreeze preventing ice crystal forming which allows for continual function. The presence of this chemical also makes the Greenland shark’s flesh highly poisonous, acting as a defence mechanism against predators. Somniosus microcephalus also have the same body temperature as the north Atlantic Ocean between -1 to 10°C which limits the speed with which oxygen can circulate around the body, slowing the metabolism which effectively allows the sharks to sustain themselves for long periods of time without food, which suits their preferred habitat as meals can be few and far in between.
Pink goblins of the deep
Another shark which can be found in the deepest oceans is the Goblin shark Mitsukurina owstoni – they are the deepest living sharks and can found in living depths between of up to 1300m. They have a wide global distribution as they have been caught in all three major oceans including Pacific, Atlantic and Gulf of Mexico. They can be found in the most extreme habitats from submarine canyons in southern japan to seamounts along the Mid-Atlantic ridge. Although these creatures may appear pinkish in colour, these sharks actually have translucent dermis that enables us to see the oxygenated blood within their capillaries, this is due to these capillaries being so close to the skin surface of the animal. Little is known about these creatures, however everything you can observe from the physiology and biology of these animal exhibits the harsh reality of the deep sea habitat it lives in. As you can see from the GIF below, they have soft muscles and flabby skin, which suggests that the Goblin shark is not a strong swimmer, conserving its energy to live a life of lethargy. Goblin sharks are also famous for their protruding jaws, this feature enables fast prey capture, higher hunting success with low energy usage. Its cartilaginous skeleton is simple and poorly calcified which reflects the lack of nutrients found in these extreme habitats. Like the Greenland shark, the anatomy of these sharks also suggests them to be relatively inactive.
A Cryptozoologist’s Sea Serpent
The Frilled shark Chlamydoselachus anguineus is arguably the most primitive species of living shark – it is a deep water-dwelling mystery, very little is known about the species. They are found over the outer and upper continental slope as deep as 1,570m and as you can see from the image on the left acquire an eel like appearance reaching lengths of 2m. These elasmobranchs have a patchy global distribution, found in areas such as New Zealand, West Africa and Chile and have a preferred temperature 0f < 15 °C. Frilled sharks are known to have a poor calcified skeleton similar to goblin sharks and a large liver with low density lipids, which allows them to maintain a constant position in the water column with little effort. Similar to the Greenland shark, the intensity of the cold deep sea it inhabits makes the metabolic cycle of this shark somewhat lethargic, comparing to that of the fast moving Scalloped hammerhead sharks which have a very high metabolic rate due to the warm waters they inhabit.
Lava Shark – fact or fiction?
In July 2015, a camera was dropped into the crater of a sub-marine volcano off the Solomon islands in order to research the area for hydrothermal activity, however what was discovered was beyond what ocean engineer Brennan Phillips and his team of researchers could have ever imagined. Scalloped Hammerhead sharks Sphyrna lewini and Silky sharks Carcharhinus falciformis were discovered living inside Kavachi: one of the most active submarine volcanoes in the Pacific. The incredible video footage was recorded in and around the active volcano. Although, relatively little is known about this new discovery so far, it is thought that the exposure to acidified water caused by an increase in carbon dioxide can cause changes in shark sleeping patterns and behaviour. Last September, marine biologists from University of Gothenburg in Sweden discovered that exposure to acidified water can cause changes in shark behaviour. Acidified ocean water, caused by an increase in carbon dioxide, causes sharks to swim for longer periods without sleeping and it can affect how well they sense their prey by scent.
This video shows the sharks found inside the active volcano, exhibiting the extreme environments they can colonise.
This discovery has brought up a lot of questions of how much we actually know about sharks. There is no way any organism could live in an erupting volcano, so why do sharks inhabit these risky environments? Do sharks have some sort of detector that the volcano is going to erupt? Very little is known, leaving opportunities for future research and further analysis on the biology of these organisms, however the cost and risk of conducting this research in this extreme marine environment may leave scientists facing further limitations.
So what do we know now?
The adaptive features that deep sea sharks exhibit whether it be the glacial pace of their movements, low metabolic rate to cater for the lack of food in the deep sea or high metabolic rate for high temperatures inside a volcano, TMAO present in greenland sharks or poorly calcified bone structure of the Goblin Shark. All features show that these sharks are highly adaptive to some of the most extreme temperatures, depths and pressures. However due to deep sea research being restricted by physical limitations, deep sea sharks truly are aliens of the deep and are the least researched elasmobranchs on the planet. They have some of the most fascinating adaptations and charismatic features which may hold important biological information to gain a further understanding on many more species of Elasmobranchii. By researching these sharks, we may get an insight into the extreme habitats they belong to and what benefits they may present to organisms.