Floating was easy on the currents of the blue, blue sea.
But then hunger happened and it was no longer sufficient to float without aim. It was necessary to grow.
First there was plankton, then the smallest of fishes to be souped and absorbed.
Soon they were large enough to engulf the biggest fish and take what was needful from the crying corpses. Nobody cared when they harvested the ocean, but when they took drylander prey, with its sweet flesh, the hunter became the hunted.
The flying machines dropped their bombs, and one jelly became one million hungry floating beings.