its quite easy to sink to the bottom and have significant weight to achieve this if you simply exhale a fair amount of air...

of course, it means you can't do it for long, and taking up a position like that probably isn't a good idea when you have purposely emptied your lungs of oxygen, but hey... who am i to stop anyone from trying.

that said, this is a non-existant creature...

are we really that concerned about underwater physics over fap material?