Giant squid exist and use the only option to get big (e.g. being a boneless blob) in the deep that we know.
There is barely anything to eat in the deep, a giant would have to feed from some underwater source that is again not known to us, which is pretty unlkely because we know a lot about earth's geology.>>455>scientists
Well, corporations is a better choice because they are much more numerous and less careful to potential damage.
That is a better scenario but lokking at the bottomless pit of the sea sure makes me thing of unholy creatures with villainous intentions.