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In our recent video, the first of our Making Monsters series we dove head first into dragonology and the genetic clockwork that would allow us to make them, well real. We spent most of the video focusing on flying fire breathing monsters, and then a smattering of other iconic beasts of legend and anime. We covered great sea worms claiming that if we wanted gigantic monsters, the ocean was the best place to find them. But why do animals grow so big in the oceans? What makes gigantism possible in the dark depths of our world? Let us dive into deep sea gigantism!
First off we have to cover the obvious, buoyancy in water allows for organisms to support much larger weights than anything could on land. That’s a given, and whales living in the shallows can still dwarf anything that has to walk on terra firma. But even within the waters there are 2 trends that we cannot ignore when it comes to body sizes, specifically polar and deep sea gigantism. The former is an observed tendency for similar animals to grow much larger as we approach the poles as their more temperate cousins. The latter is again an observation that similar animals who live at abyssal depths are gigantic compared to their shallow water counterparts. This is especially noticeable in crustaceans, compare the crabs found in the shallows to the giant Japanese Spider Crab for example, as well as with cephalopods, most notably the giant and colossal squids. These are of course invertebrates and don’t really relate to our giant wyrms of legend, but some of you may already be asking about anguilliforms (eels) and the giant oarfish. If there is ever a body plan to start with for a Jörmungandr like giant of the deep, it's the oarfish holding the record as the longest boney fish with measured lengths of 7 to 8 meters and it’s estimated they could reach up to 11m and weigh as much as 272kg (600lbs).
There are a few factors that have been put forth explaining these two forms of gigantism; low temperatures, food scarcity, reduced predation and increased dissolved oxygen.
It’s interesting to look at the gigantism in a polar water column as opposed to a tropical one, there we can notice that the proportional gigantism of the creatures of the deep are much lower if not entirely absent. This is to say, that the creatures at the poles are big at all levels, whereas nearer the equator, gigantism is correlated to the depth. It would appear that the cold temperatures experienced by creatures living in these places has a great impact on their size. We have also observed this tendency of animals on firm ground to grow bigger in colder climes. The bigger an animal becomes, the more insulation they gain while at the same time lowering their proportional surface area. Bigger animals are more efficient at managing their heat, which is essential for biological processes to occur. On top of that, the cold waters reduce the chemical activity and these creatures end up with slower metabolisms and bigger cells. This means that they’re less likely to make transcription errors, or be damaged by energetic processes, leading to longer lives. The more time a being lives, the longer they can keep growing.
One could imagine that a larger body would be harder to maintain when food is scarce, but a larger body allows creatures to move further, whether it be by drifting as many cnidarians (jellyfish) or cephalopods do, or by swimming swimming like the Greenland shark, or walking like the giant Japanese spider crab. As beings grow in size, the proportional energy necessary to cross great expanses is lesser than if they were tiny. Anyone who’s ever walked anywhere with a toddler, or had a small dog on a leash has experienced this first hand. Then if food is scarce, the ability to stockpile large amounts of lipids as a store of energy is a major advantage of size.
What came first, the large animal that is too big to hunt or the fact there was nothing hunting it in the first place letting it grow to its final size? Well research, seems to indicate that predation at depths is at least an order of magnitude lower than on the surface, at least for the brachiopods concerned. So it’s possible that the low rate of interaction between species and the scavenger focused lifestyle has left most animals with little to no predators, thus allowing them to continually grow.
As we go down through the water column, the salinity of the water decreases as the density forces start to take effect, which in combination with lower temperatures and higher pressures mean that the concentration of dissolved oxygen can be significantly higher than at the surface. Though the higher solubility does not necessarily equate with the availability of the oxygen. A proposed theory posits that the size of the animals increases the exchange surfaces preventing asphyxia.
And there we have it, the evolutionary pressures that lead to gigantism and a target organism to modify. We’ve been doing a lot of research for our next making monsters video, and um the oceans are scary y’all!
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