No oxygen bar appears when in seaweed.
In the sea, mobs spawn and Squids are choking in kelp.
Squids "drowns" underwater in the ocean plant
Kelp acting as Air Blocks
Kelp and seagrass act like pockets of air
You receive air when inside an underwater and never drown.
Kelp gives air pockets
Hacked water blocks with a collision box allows breathing
Fishing rod cannot catch fish when the bobber is in hacked water