Human talk about their oceans flora and fauna and deep water creatures.
Needless to say, it only adds more reasons, why Humans and their Deathworld should have been classified way higher. -- Anon Guest
Humans love to explore. To them, nothing is more alluring than the path not taken, the nook unchecked, or the depths undelved. There is no length a Human will not go to in order to see what's there just because they can. It should therefore surprise few that, once exploring a new world, they will bring their light and curiosity to the deepest, darkest depths.
Especially if those depths are underwater. They've spent centuries developing technology that would give them access to places they otherwise couldn't go. Including the depths of their neighbouring gas giants. It should not have been a surprise to see Human Jan using the Bulk Fabricator to print a high-pressure exploratory vessel, replete with Sonar HUD technology that would turn the windows into displays where, in Human Jan's words, the people within would be able to 'see like a dolphin'.
"Why?" Kikroth demanded. "There is very little below the light layer. No plants or plant-like life can exist without sunshine. Therefore, there's nothing for anything else to live off."