Why Do Deep Sea Creatures Evolve Into Giants?

the deep sea is vast dark and nearly freezing cold and it is also full of giants as we begin to descend the ocean depths we first pass through the epipelagic zone here is where almost all ocean life exists thanks to the sun's penetrating energy here animals are colorful and abundant next we reach the mesopelagic zone also known as the ocean twilight zone here light becomes very dim and photosynthesis becomes impossible below a thousand meters all sunlight disappears and we enter into the midnight zone or the bathypelagic zone the only light that can be seen down here is the glowing bioluminescence from the skin of squids or the lures of anglerfish the pressure here is immense the temperature's shockingly low but the ocean goes deeper still the abyssal pelagic zone reaches depths of up to 6 000 meters with pressure 600 times that of our terrestrial world the abyssal realm is considered the single largest ecosystem for life on earth covering 300 million square kilometers about 60 percent of the surface of the globe but the deepness of the ocean doesn't stop there the hedo pelagic zone is the deepest ocean region it's found from a depth of about 6 000 to 11 000 meters and exists in long narrow topographic v-shaped trenches the deepest of these ever discovered is the mariana trench and despite all logic life survives in these darkest depths and the creatures here have evolved to be exceedingly freaky from the ghostly to the terrifying to the absolutely gigantic the giant japanese spider crab the big red jellyfish the king of herring's oarfish the giant squid the greenland shark and the giant isopods these animals are all examples of deep sea gigantism the tendency that deep sea animals have to be substantially larger than their shallow water counterparts in waters intensely cold and dark why do these leviathans emerge is it an eerie coincidence of the deep dark sea or a feature of life in this inhospitable landscape [Music] below 400 meters food becomes quite scarce in the ocean as sunlight tapers off photosynthetic algae and plankton disappear too and without this crucial part of the food chain life gets markedly harder for deep sea animals instead most of them have to rely on detritus that rains down from shallower waters a phenomenon called marine snow marine snow is mainly composed of dead plankton fecal pellets and bits of rotting corpses that fall to the sea floor as fine particles some animals rely directly and completely on marine snow the vampire squid for example has special adaptations to help them better catch and eat the falling particles two long filaments extend from their bodies to capture any that drifts past them in their habitat 900 meters deep marine snow is the backbone for all life in the deep but it can't support a great deal of biomass the number of creatures in the deep is sparse and the food web is strained many animals don't eat marine snow directly but rely on eating those that do and thus the pressure of predation is extremely high any small fish crustacean or cephalopod has a big target on its back from any larger predator and for this reason it became evolutionarily advantageous for animals to get rid of this target on their back to transition from being a prey animal into a top predator enter the giant squid both an icon and an enigma of the jeep by the turn of the 21st century the giant squid remained one of the few extant megafauna to have never been photographed alive what we know about the giant squid largely comes from specimens that have washed ashore it wasn't until 2004 that the first photographs of a live giant squid in its natural habitat were taken in the twilight zone at a depth of about 1 000 meters and while we may not know much about these mysterious creatures we do know that they are huge the largest individual ever found was 13 meters long as long as a school bus and weighing 275 kilograms compared to the majority of squid which are no more than 60 centimeters long these giants are truly exceptional scientists believe that by having such a tremendous size they're left with few predators and allows them to comfortably prey on deep sea fish and other squid species which they grab with their two extremely long tentacles but as impressive as the giant squid is it is not the largest of the deep sea squids the colossal squid sometimes called the antarctic squid is the largest invertebrate in the world they're shorter in length than the giant squid at only 10 meters but can weigh between 500 and 700 kilograms lurking in depths over 2 000 meters it's easy to imagine such a massive creature as an aggressive top predator darting through the water snatching prey and dominating its adversaries ripping sailboats apart etc but this squid teaches us something else about deep sea giants they aren't necessarily the dominating predatory force we imagine because with their large size comes something else an extremely slow metabolism the colossal squid takes something called klieber's law to the next level klieber's law states that metabolism doesn't scale linearly with body size as you might predict a horse that weighs a thousand times more than a mouse doesn't require a thousand times more energy instead of metabolism scaling linearly with body size it scales with an animal's mass to the three-quarters power this applies to all life on earth from blue whales right down to individual cells it's largely a consequence of the physics and geometry of animal circulatory systems an animal's surface area to volume ratio and the fractal nature of blood vessels and all this means that the larger an animal is the more efficient it is and the colossal squid seems to be exceedingly efficient one study estimated the metabolic rate of the colossal squid to be so low that they only burn 45 calories per day and only require 0.03 kilograms of food per day a single adult tooth fish would be enough food for a 500 kilogram colossal squid for approximately 200 days their energy requirements are 300 fold to 600 fold lower than other similarly sized top predators of the southern ocean this indicates that the colossal squid has a particularly slow pace of life it doesn't chase down its prey in epic battles like we might imagine instead it sits and waits for prey to unwittingly approach then uses the hooks on its arms and tentacles to ensnare it this opportunistic lifestyle also makes sense because in water so deep visual predation would be nearly impossible due to extremely limited visibility the colossal squid does have the largest eyes of any animal in the world up to 30 centimeters wide but scientists believe these eyes are not for catching prey but for detecting and avoiding predators not many creatures could hunt a squid so large but a select few can most notably sperm whales food scarcity and predator avoidance are some of the major pressures for deep sea animals to grow so large and have such slow metabolisms but they are not the only pressures the deep cold water itself forces such gigantism to occur birdman's rule states that animals found in cold environments will be larger than those found in warm environments this rule however has historically only been found to be definitively true for endotherms the warm-blooded animals like birds and mammals does this trend also apply to ectotherms the squids crabs and isopods that inhabit the deep it's a surprisingly controversial area of science but it's clear that certain species of ectotherm are indeed larger at colder temperatures this can certainly be seen in the polar regions of the earth where marine sponges worms and even single-celled organisms get huge and where the waters deep and polar there's one of the strangest giants of them all the greenland shark is the largest fish in the arctic ocean and one of the largest sharks on earth seven meters long and weighing as much as fourteen hundred kilograms it lives at depths over two thousand meters where the water temperature is between negative two and seven degrees celsius it's the only shark that can withstand the cold waters of the arctic year round and this extremely cold environment has caused the shark to not just be huge but ancient greenland sharks are the longest living vertebrates in the world so old that there are likely individuals swimming in the sea that were alive before christopher columbus voyaged to the americas before michelangelo painted the sistine chapel while the aztec and incan empires were still thriving scientists estimate their average lifespan to be at least 272 years with some individuals living perhaps well over 500 years inside the shark's eyes there are proteins that form before birth that are then covered by many layers of the lens of the eye these proteins do not degrade with age so by carbon dating them scientists can roughly determine the age of the shark one five meter female was assessed to be between 272 and 512 years old these sharks don't even reach reproductive age until around 150 years old their astoundingly long life can be attributed to their exceedingly low metabolism much like the colossal squid and just like the colossal squid they are extremely slow and opportunistic feeders they eat some fish and squid and scavenge any carcass they can find their stomach contents have even included polar bears horses and reindeer just like the giant squids they too would struggle to spot and chase prey in the pitch-black waters but even if the water wasn't so dark the sharks still couldn't see because a particular crustacean constantly latches on to their eyeballs damaging them to the point of total blindness the thought of drifting along in negative two degree pitch black water for 500 years with crustaceans attached to your eyeballs gives me heebie-jeebies of the highest order the animals we've discussed so far are certainly strange incredible and even creepy but we've only gone as deep as the miso and bathypelagic zones two hundred to four thousand meters down the ocean goes deeper still and reveals one of the most extreme cases of deep sea gigantism ever discovered in the hadel trenches six thousand to eleven thousand meters deep the temperature varies between one and four degrees celsius there is no light and the pressure can reach levels eleven hundred times that of the surface here the marine snow that gives life to most of the deep barely trickles down ninety percent of it never reaches past the twilight zone at these depths it seems like life should be impossible but instead the deeper you go the more you'll find colossal amphipods crawling along the bottom shallow water amphipods are usually around 5 millimeters to 20 millimeters in length but these deep water behemoths can grow up to 34 centimeters long something that's often the size of a gnat at these depths is the size of a guinea pig alicella gigantea is known as the supergiant amphipod and is the largest amphipod ever discovered their gigantism is similar to that of the giant isopods that can measure up to 50 centimeters long their roly-poly cousins you might find in your garden are a mere six millimeters long these amphipods and isopods are scavengers and detrivores eating any decomposing material they can find and their large body size may help them store as much food and energy as possible when they can find it relatably when giant isopods find a significant food source they gorge themselves to the point of compromising their locomotive ability by doing this they can survive long periods of famine giant isopods have been known to survive over five years without food in captivity their large body size also allows them to travel greater distances in search of their next meal another reason for their huge body size might have to do with the viscosity of the water at such depths and cold temperatures down there water would feel thicker than water at the surface larger body size may give these deep sea invertebrates a respiratory advantage that helps them overcome the larger viscous forces in the water but even with all these factors it's still hard to comprehend how there could be enough food at these depths to support these giants but recently researchers discovered that some of these creatures might be feeding on an entirely unexpected food source one hadal amphipod hierondalia gigas was found to have a unique cellulase enzyme one that seemed like its purpose was to break down plant matter this was surprising because absolutely zero plant life can live in the hadel depths and the amphipods wouldn't need this enzyme to digest bits of algae in the form of marine snow yet when scientists tested the enzyme it converted sawdust and wood pulp directly into glucose and on top of this its enzymatic activity increased under high hydrostatic pressure the higher the pressure the faster and more efficiently the enzyme could digest cellulose there may be no plants living in the hadel zone but on occasion large pieces of driftwood will sink all the way to the bottom of the deepest parts of the sea and being able to convert this wood directly into energy is of high survival value for an animal that doesn't have many options while we don't know much about the deep sea we do know that it's a very delicate ecosystem many of these animals already live on a knife edge of survival and any change to their environment could mean the end for these giants overfishing plastic pollution changes in ocean chemistry due to climate change and deep sea mining are all threats to this incredible ecosystem these creatures may seem like they live in a far off alien planet but it's still very much connected to and dependent on ours and scientists now believe we very well may be dependent on their world too we are only beginning to understand the intrinsic connection between ocean ecosystems and the links between them and the terrestrial environments in which we live and most importantly who wants to live in a world that's been stripped of its wonder of its dazzling mesmerizing and baffling deep sea creatures we as a species are so focused on trying to find alien life on other planets that we often forget about the unthinkable creatures that are living right under our noses or rather under many miles of ocean if you're like me the news in the world lately makes you desperately wish you too lived at the bottom of the ocean maybe the greenland shark floating alone in the darkness with parasites on its eyeballs is actually onto something i bet the greenland shark doesn't doomscroll itself into insomnia every night or begin the day with a cup of anxiety reading the front page of reddit and all its associated threads of arguing and stupidity but since i am unfortunately a human i often do exactly these things i want to stay informed but then find myself getting sucked into the news in social media working myself up trashing my mental health and honestly wasting a lot of time so this is why i've switched my morning news routine to morning brew morning brew can't make the news better but it can make it understandable and digestible morning brew gets you up to speed on business finance and tech in just 5 minutes and their recaps are refreshingly witty there's no comment section to accidentally fall into so you can read about elon musk and twitter's feud with just the information and not the fanboy commentary or you can quickly understand what's going on with the stock market without the speculation and the best part of all of this is it's completely free plus by signing up you are greatly supporting this channel if you've ever thought about signing up to any of our sponsors now is the perfect time all it takes is 15 seconds and an email address so to get a new and improved morning news routine click the link in the description to get started with morning brew today and if you'd like to watch something else right now you should watch our previous video about the world's deadliest snake or watch real engineering's latest video about the engineering of self-healing spacesuits [Music] you

Channel: Real Science

Views: 3,204,060

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Id: uYR4ZMlLUwI

Length: 19min 13sec (1153 seconds)

Published: Sat Jul 16 2022