The deep range - Arthur C. Clarke

Since the beginning of time it had worked its will on humanity, and for as long as man could remember, he had struggled against its power. But in the 21st century the battle was won: the sea, mankind's age-old enemy, had finally been conquered.

Professionals like Walter Franklin now patrolled the infinite savannahs of the oceans, harvesting from the plankton prairies as crop which kept the world fed. But like that other great frontier, space, the sea had not yet yielded up all its secrets. And men like Franklin would never rest until its every fathomless mystery had been challenged . . .