what limits how large a marine animal can grow? What biologically prevents a kraken from existing?
In: 2
One reason is the food supply that have been already mentioned
The second reason why living beings can’t grow past certain limints is the limited toughness of tissues. No matter how large or how small a creature is, it’s living tissues are made from the same atoms (mostly carbon, hydrogen and oxygen). These atoms have fixed size and connect to each other with fixed force no matter big or small animal. If the piece tissue gets really really big, it starts to collapse under the weight of it’s own atoms basically, that’s why we can’t just build skyscrapers reaching orbit, for example. A very big creature would just collaps under it’s own weight or be very susceptible to forces like water currents.
The third reason is the [square-cube law](https://en.wikipedia.org/wiki/Square%E2%80%93cube_law#:~:text=The%20square%E2%80%93cube%20law%20can,the%20cube%20of%20the%20multiplier.). Basically, when you gradually make a creature bigger, it’s weight will grow at a higher rate than it’s muscle strenght, so compared to it’s own weight the creature will get weaker and weaker, until it will not be able to survive.
The latter two reasons are not as important for the sea animals, given that the mass of water supports the aquatic animals and allows for the largest animals on Earth to exist, but they are still important.
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