Neat!

Yeah great point sunlight only penetrates so far into water, and plant life I think is classified as using photosynthesis

The Sargasso Sea has lots of seaweed, but I hear your point, it’s not the base state of the ocean to be filled with plants

Plankton can be plants or animals, there are a lot of those

Extremely shallow people, and VERY insecure will always care about this sort of thing