Idea for the boundaries of the map

Cyion

What if when you reached the boundaries of the map where all the cliffs are, there are giant worm-like creatures in caves in the cliff walls that pop out and try to eat your seamoth (can swallow it whole) and the cyclops it will try to eat but cannot quite stomach it. So the cliff side would be riddled with these caves and each cave has one of these worms.

Sigmalx

it could be this is partly a giant hoodoo, so when areas exceed the boundaries, they exceed the safe areas to move and descend, as at the deepest we can go, we haven't entered the midnight zone (2Km beneath the surface)

I found a nice map
0m-200m is the epipelagic zone or the sunlight zone
201m-1000m(or 1Km) is the Mesopelagic zone or the Twillight zone. this is when you will start loosing light fast, and the terrors of the deep start to reside.
1001m-4000m is the Bathpelagic zone or the Midnight zone: light stops at 1000m underwater, the deepest place in subnautica descends to about 2000 meters, in the Emperor Facility.
beyond that 4000m is the Abyssalpelagic and the Hadalpelagic (or the Hadal) zones. Abyssalpelagic is name sake give away, but a Hadal is a deep water trench 6Km below the surface of the ocean and beyond.
https://rdt-oceanography.wikispaces.com/file/view/ocean_zones.jpg/304102942/ocean_zones.jpg I used this to refresh my knowledge on the oceanic zones.