Only just realized this when watching a diving video.
But why isn’t the ocean full of massive plants? The surface of the earth is covered is giant trees working to fight against gravity, wind, and fire.
But in the ocean you have little things like coral beds and sponges and maybe a kelp forest.
Seeing as weight is massively reduced, and the closer you get to the surface means more light, and water and nutrients are probably plentiful… Why isn’t the plant life more massive? What is the limiting factor to things evolving to be bigger?
Only thing I can think of is CO2 perhaps?
Land based plants exist in an arms race between access to sunlight and water/nutrients. They have to physically occupy two separate areas. In contrast, water based plants only need to occupy one location, the water closest to the surface. Since there is no evolutionary advantage to starting to grow tall, water based plants don’t grow as tall.
Seaweed grows large, but it doesn’t need the kind of rigid structure trees have.