The ocean is literally an alien world with different laws of gravity, a different atmosphere, different everything, and it is teeming with all sorts of diverse and unique life that thrive in all sorts of crazy environments and conditions. immense pressure, complete and eternal darkness... Thousands of species that we know of and hundreds of thousands that we don't who exist in a world without sunlight or oxygen. And we know that at least some, more realistically, quite a few, possess developed intelligence equal to or arguably even greater than our own.