Why The Ocean Breeds Giants

Have you ever wondered why deep sea creatures have got excess pituitary growth hormone secretion in their bodies?

Well, these baffling, mysterious and spooky giants, the top predators who seem to be beating each other black and blue haven't got an easy way out.

With immense pressure and shockingly low temperatures, the creatures here have turned out to be extraordinarily humongous and freaky at the same time. As sunlight tapers off, photosynthetic algae and plankton disappear. This disrupts the entire food chain, making it more difficult for deep sea creatures to cope. MARINE SNOW comes to the rescue, it's the detritus showering from shallow regions falling on the sea floor as fine particles. Some creatures depend completely on marine snow. The Vampire Squid, for example, has a special adaptation to grab it to the fullest. 

But the marine snow can't support the whole of the deep biomass. The food web is strained. Many other organisms consume marine snow indirectly, thereby immensely increasing the predation pressure. Large size, evolutionarily favoured them, converting them from prey animals to top-class predators. These organisms have taken Kleiber's law to the next level! This law states that metabolism doesn't scale linearly with body size, it scales with the animal's mass to ¾ of the animal's power (small animals respire more per unit of body mass than larger animals because a larger fraction of their body mass consists of metabolically active tissues that have higher maintenance costs as opposed to reserve tissues that consume comparatively lower resources). 

With extremely large size comes an incredibly SLOW  metabolism compensating for food scarcity and predation pressure. For instance, the Colossal Squid, 10 metres long, weighing up to 500kgs, lurks in depths over 2000 metres. It's easy to imagine such a massive creature as an aggressive predator darting through the water, dominating its adversaries. But it teaches us something else, their large size is accompanied by extremely slow metabolism allowing them to survive for approximately 200 days consuming a single adult toothfish (as per one theory). Their energy requirements are 300-600 folds lower than other similar-sized top predators of the southern ocean. This proves their exceedingly amazing efficiency! Visual predatory violence seems quite unrealistic. Coming to their large eyes(perhaps the largest) aren't meant for vision but for detecting and avoiding predators (most notably sperm whales).

But this isn't the only thing leading to such gigantism, indeed cold water has forced them to take up such a body size. It's a surprisingly controversial area of science. But it is clear that certain species of ectoderm are huge at cold temperatures. The Greenland shark is a living proof of the same. This 7metre long creature lives at depths over 2000 metres where the temperature ranges between -2 to 7 degrees Celsius making it the only shark to withstand the cold waters of the Arctic. Inside the shark's eye, are proteins that are formed before birth, which are then covered by many layers of the lens of the eye. They do not degrade with age, thereby allowing scientists to estimate their age by carbon dating. One five-metre female was assessed to be between 272 to 512 years old. These sharks don't even reach reproductive maturity until 150 years. Their astoundingly long life can be attributed to extremely low metabolism.  And just like the colossal squid, they are extremely slow and OPPORTUNISTIC feeders. But we've gone as deep as Mesopelagic and Bathypelagic zones. 

The eternal ocean goes still deeper, revealing extreme cases of deep-sea gigantism. In the Hadal Region, 6000 to 11000 metres deep, the temperature varies between 1 and 4 degrees Celsius with pressure as high as 1100 times that of surface level. Even marine snow barely trickles down this very part of the ocean. But the deeper you dig, the more intertwined mysteries open up. The deep water Bohemiths grow up to 34cm while their rollie pollie shallow water cousins are just 5 to 20 mm long, eating any decomposing material they can find. These giant isopods can survive up to 5 years without food in captivity. Their large body also allows them to travel greater distances in search of their next meal. 

Large body size also seems to provide a ‘respiratory advantage' to overcome the viscous forces of cold water. While these creatures may have entirely unexpected food sources, one Hadal amphipod was found to be possessing a unique cellulase enzyme. This was mind-boggling for the scientists as well because absolutely zero plant life exists in this region. Being tested, this enzyme was found to convert wood pulp and sawdust into glucose. The higher the hydrostatic pressure, the greater the enzymatic efficiency.

These creatures have developed unique pressure-withstanding abilities as well. Firstly, the presence of TMAO(trimethylamine oxide) in deep-sea fish prevents the distortion and compression of proteins and other vital molecules within the body under intense external pressure. Secondly, lack of nitrogen absorption at deep pressure prevents the development of nitrogen narcosis and decompression sickness. Thirdly, completely compressible lungs which, under pressure collapses, forcing all of the gas from the lungs out into the muscles and bloodstream where the gas is dissolved. The muscles are adapted to hold more myoglobin while the blood possesses more haemoglobin for the storage of oxygen. Collapsing of the lungs results in reduced air pockets and minimum oxygen available for its survival. 

While we don't know much about the deep sea, we do know that it supports a much DELICATE ecosystem, wherein the animals are living on a knife-edge survival and any single change in the environment could mean the END of these giants. These creatures may seem living in a far-off alien planet, but it's still very much connected to and dependent on ours.