Answer:
not sure if you still want an answer, but here:
the further down you go, the colder it'll get because the sunlight won't reach down as far, also making it darker. the pressure will also keep building up until it gets to be too much for your body to handle and literally crushes you.
the density of the water will keep crushing you until you are DEAD
Explanation:
This is a wild guess but I'm gonna say its Predation.
a. Stabilizing selection
