However, storing hydrogen is probably infeasible for biology. It's difficult to store hydrogen, even using metal containers without it leaking out, because the molecules are so small.
Granted there are also opportunity costs to everything - rabbits dominated Australia comically despite the widespread deadliness by investing in reproduction and evasion instead of dangerous defense mechanisms.
One problem with floating plants is that dirt and water are heavy.
James Cameron stated he has been a passionate scuba diver and it was a slight nod to others who may have had similar experiences.
[0] https://www.startalkradio.net/show/ [1] https://www.startalkradio.net/show/the-spirit-of-exploration...