The first step in the Deep Sentinel program, one of the most ambitious ocean-engineering projects in decades, will be completed this year. This initial step, called Vanguard, will shelter three aquanaut-scientists at depths of 100 meters. Eventually, the project will create a modular underwater habitat system that will let scientists live underwater for weeks at a time.
Humans are the ones tooling and retooling these units for specific purposes, which can be done far more efficiently in situ in an underwater habitation. Along with any other human activities that will be occurring, such as immediate study in a dedicated lab facility.