Weird, huh? A body of water within another body of water. Yes, these mini ecosystems do exist. Also known as “brine pools”, they are super-saline lakes at the bottom of the ocean, more specifically, in the Gulf of Mexico. It is caused by salt tectonics where the high salinity of the water in the pool prevents lower salinity waters from mixing and creates a distinct surface and shoreline for the pool. They even have their own shores! Waters used to be shallow in the Gulf of Mexico and cut off from the ocean during the Jurassic period. It left a thick layer of salt and other minerals up to 8km thick after it dried. Ocean water returned to the region after is rifted apart transforming the area into an underwater lake. The brine continues to feed the lake where it is released from a rift in the ocean floor.
You would think hardly any organisms survive here because of the extremely high salinity, right? Wrong. Extremophiles have found a way to adapt to these extreme conditions. Some organisms utilize abundant methane, while others are chemosynthetic organisms.