While in a marine biology class I'm taking we watched the film Blue Planet 2. It's essentially a sequel to the first blue planet, which is all about the ocean and the life in it. During the episode 'Take a Deep Breath', aka deep sea, it was revealed to me that such a phenomena does infact exist.
In deep sea, pools of stuff called brine can build up. It's much denser than water, so it settles at the bottom - but it is a liquid. The episode showed fish and eels sitting on top of the brine pools, and even swimming into them, however it is very toxic and can be lethal if in it too long.
wiki on brine pools eel suffering toxic shock from prolonged exposure to brine poolsSo essentially... in spongebob, mussel beach must be a brine pool, only logical explanation:
thoughts?