In talking with people after the fact I discovered this is a commonly missed detail in the descent to Amaurot:

You pass through several distinct biomes, each clearly intended to convey a great passage of distance and depth based on the way coral shapes and rock colors change, and finally you reach these tight, dark passages with only one monochrome coral and crystallized fossils.

You not only pass through different levels of seafloor life but through strata on your way down to Amaurot. You are not just traveling to the sea floor, you are traveling to the past and the underworld. The environment on the way down becomes rooted not in signs of life but in

signs of passage of time. This is one of the coolest details and packs a lot of atmospheric punch.

I will never stop yelling about the design of the descent to Amaurot as a whole storytelling package from set to pacing my entire LIFE.